Experimental Researches in Electricity, Volume 1 (part 4 of 4)

Experimental Researches in Electricity, Volume 1 (part 4 of 4)

1533. It is curious to observe the relation of glow, brush, and spark to each other, as produced by positive or negative surfaces; thus, beginning with spark discharge, it passes into brush much sooner when the surface at which the discharge commences (1484.) is negative, than it does when positive; but proceeding onwards in the order of change, we find that the positive brush passes into glow long before the negative brush does. So that, though each presents the three conditions in the same general order, the series are not precisely the same. It is probable, that, when these points are minutely examined, as they must be shortly, we shall find that each different gas or dielectric presents its own peculiar results, dependent upon the mode in which its particles assume polar electric condition.

1534. The glow occurs in all gases in which I have looked for it. These are air, nitrogen, oxygen, hydrogen, coal gas, carbonic acid, muriatic acid, sulphurous acid and ammonia. I thought also that I obtained it in oil of turpentine, but if so it was very dull and small.

1535. The glow is always accompanied by a wind proceeding either directly out from the glowing part, or directly towards it; the former being the most general case. This takes place even when the glow occurs upon a ball of considerable size: and if matters be so arranged that the ready and regular access of air to a part exhibiting the glow be interfered with or prevented, the glow then disappears.

1536. I have never been able to analyse or separate the glow into visible elementary intermitting discharges (1427. 1433.), nor to obtain the other evidence of intermitting action, namely an audible sound (1431.). The want of success, as respects trials made by ocular means, may depend upon the large size of the glow preventing the separation of the visible images: and, indeed, if it does intermit, it is not likely that all parts intermit at once with a simultaneous regularity.

1537. All the effects tend to show, that glow is due to a continuous charge or discharge of air; in the former case being accompanied by a current from, and in the latter by one to, the place of the glow. As the surrounding air comes up to the charged conductor, on attaining that spot at which the tension of the particles is raised to the sufficient degree (1370. 1410.), it becomes charged, and then moves off, by the joint action of the forces to which it is subject; and, at the same time that it makes way for other particles to come and be charged in turn, actually helps to form that current by which they are brought into the necessary position. Thus, through the regularity of the forces, a constant and quiet result is produced; and that result is, the charging of successive portions of air, the production of a current, and of a continuous glow.

1538. I have frequently been able to make the termination of a rod, which, when left to itself, would produce a brush, produce in preference a glow, simply by aiding the formation of a current of air at its extremity; and, on the other hand, it is not at all difficult to convert the glow into brushes, by affecting the current of air (1574. 1579.) or the inductive action near it.

1539. The transition from glow, on the one hand, to brush and spark, on the other, and, therefore, their connexion, may be established in various ways. Those circumstances which tend to facilitate the charge of the air by the excited conductor, and also those which tend to keep the tension at the same degree notwithstanding the discharge, assist in producing the glow; whereas those which tend to resist the charge of the air or other dielectric, and those which favour the accumulation of electric force prior to discharge, which, sinking by that act, has to be exalted before the tension can again acquire the requisite degree, favour intermitting discharge, and, therefore, the production of brush or spark. Thus, rarefaction of the air, the removal of large conducting surfaces from the neighbourhood of the glowing termination, the presentation of a sharp point towards it, help to sustain or produce the glow: but the condensation of the air, the presentation of the hand or other large surface, the gradual approximation of a discharging ball, tend to convert the glow into brush or even spark. All these circumstances may be traced and reduced, in a manner easily comprehensible, to their relative power of assisting to produce, either a continuous discharge to the air, which gives the glow; or an interrupted one, which produces the brush, and, in a more exalted condition, the spark.

1540. The rounded end of a brass rod, 0.3 of an inch in diameter, was covered with a positive glow by the working of an electrical machine: on stopping the machine, so that the charge of the connected conductor should fall, the glow changed for a moment into brushes just before the discharge ceased altogether, illustrating the necessity for a certain high continuous charge, for a certain sized termination. Working the machine so that the intensity should be just low enough to give continual brushes from the end in free air, the approach of a fine point changed these brushes into a glow. Working the machine so that the termination presented a continual glow in free air, the gradual approach of the hand caused the glow to contract at the very end of the wire, then to throw out a luminous point, which, becoming a foot stalk (1426.), finally produced brushes with large ramifications. All these results are in accordance with what is stated above (1539.).

1541. Greasing the end of a rounded wire will immediately make it produce brushes instead of glow. A ball having a blunt point which can be made to project more or less beyond its surface, at pleasure, can be made to produce every gradation from glow, through brush, to spark.

1542. It is also very interesting and instructive to trace the transition from spark to glow, through the intermediate condition of stream, between ends in a vessel containing air more or less rarefied; but I fear to be prolix.

1543. All the effects show, that the glow is in its nature exactly the same as the luminous part of a brush or ramification, namely a charging of air; the only difference being, that the glow has a continuous appearance from the constant renewal of the same action in the same place, whereas the ramification is due to a momentary, independent and intermitting action of the same kind.

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Dark discharge.

1544. I will now notice a very remarkable circumstance in the luminous discharge accompanied by negative glow, which may, perhaps, be correctly traced hereafter into discharges of much higher intensity. Two brass rods, 0.3 of an inch in diameter, entering a glass globe on opposite sides, had their ends brought into contact, and the air about them very much rarefied. A discharge of electricity from the machine was then made through them, and whilst that was continued the ends were separated from each other. At the moment of separation a continuous glow came over the end of the negative rod, the positive termination remaining quite dark. As the distance was increased, a purple stream or haze appeared on the end of the positive rod, and proceeded directly outwards towards the negative rod; elongating as the interval was enlarged, but never joining the negative glow, there being always a short dark space between. This space, of about 1/16th or 1/20th of an inch, was apparently invariable in its extent and its position, relative to the negative rod; nor did the negative glow vary. Whether the negative end were inductric or inducteous, the same effect was produced. It was strange to see the positive purple haze diminish or lengthen as the ends were separated, and yet this dark space and the negative glow remain unaltered (fig. 133).

1545. Two balls were then used in a large air-pump receiver, and the air rarefied. The usual transitions in the character of the discharge took place; but whenever the luminous stream, which appears after the spark and the brush have ceased, was itself changed into glow at the balls, the dark space occurred, and that whether the one or the other ball was made inductric, or positive, or negative.

1546. Sometimes when the negative ball was large, the machine in powerful action, and the rarefaction high, the ball would be covered over half its surface with glow, and then, upon a hasty observation, would seem to exhibit no dark space: but this was a deception, arising from the overlapping of the convex termination of the negative glow and the concave termination of the positive stream. More careful observation and experiment have convinced me, that when the negative glow occurs, it never visibly touches the luminous part of the positive discharge, but that the dark space is always there.

1547. This singular separation of the positive and negative discharge, as far as concerns their luminous character, under circumstances which one would have thought very favourable to their coalescence, is probably connected with their differences when in the form of brush, and is perhaps even dependent on the same cause. Further, there is every likelihood that the dark parts which occur in feeble sparks are also connected with these phenomena[A]. To understand them would be very important, for it is quite clear that in many of the experiments, indeed in all that I have quoted, discharge is taking place across the dark part of the dielectric to an extent quite equal to what occurs in the luminous part. This difference in the result would seem to imply a distinction in the modes by which the two electric forces are brought into equilibrium in the respective parts; and looking upon all the phenomena as giving additional proofs, that it is to the condition of the particles of the dielectric we must refer for the principles of induction and discharge, so it would be of great importance if we could know accurately in what the difference of action in the dark and the luminous parts consisted.

[A] See Professor Johnson's experiments. Silliman's Journal, xxv. p. 57.

1548. The dark discharge through air (1552.), which in the case mentioned is very evident (1544.), leads to the inquiry, whether the particles of air are generally capable of effecting discharge from one to another without becoming luminous; and the inquiry is important, because it is connected with that degree of tension which is necessary to originate discharge (1368. 1370.). Discharge between air and conductors without luminous appearances are very common; and non-luminous discharges by carrying currents of air and other fluids (1562. 1595.) are also common enough: but these are not cases in point, for they are not discharges between insulating particles.

1549. An arrangement was made for discharge between two balls (1485.) (fig. 129.) but, in place of connecting the inducteous ball directly with the discharging train, it was put in communication with the inside coating of a Leyden jar, and the discharging train with the outside coating. Then working the machine, it was found that whenever sonorous and luminous discharge occurred at the balls A B, the jar became charged; but that when these did not occur, the jar acquired no charge: and such was the case when small rounded terminations were used in place of the balls, and also in whatever manner they were arranged. Under these circumstances, therefore, discharge even between the air and conductors was always luminous.

1550. But in other cases, the phenomena are such as to make it almost certain, that dark discharge can take place across air. If the rounded end of a metal rod, 0.15 of an inch in diameter, be made to give a good negative brush, the approach of a smaller end or a blunt point opposite to it will, at a certain distance, cause a diminution of the brush, and a glow will appear on the positive inducteous wire, accompanied by a current of air passing from it. Now, as the air is being charged both at the positive and negative surfaces, it seems a reasonable conclusion, that the charged portions meet somewhere in the interval, and there discharge to each other, without producing any luminous phenomena. It is possible, however, that the air electrified positively at the glowing end may travel on towards the negative surface, and actually form that atmosphere into which the visible negative brushes dart, in which case dark discharge need not, of necessity, occur. But I incline to the former opinion, and think, that the diminution in size of the negative brush, as the positive glow comes on to the end of the opposed wire, is in favour of that view.

1551. Using rarefied air as the dielectric, it is very easy to obtain luminous phenomena as brushes, or glow, upon both conducting balls or terminations, whilst the interval is dark, and that, when the action is so momentary that I think we cannot consider currents as effecting discharge across the dark part. Thus if two balls, about an inch in diameter, and 4 or more inches apart, have the air rarefied about them, and are then interposed in the course of discharge, an interrupted or spark current being produced at the machine[A], each termination may be made to show luminous phenomena, whilst more or less of the interval is quite dark. The discharge will pass as suddenly as a retarded spark (295. 334.), i.e. in an interval of time almost inappreciably small, and in such a case, I think it must have passed across the dark part as true disruptive discharge, and not by convection.

[A] By spark current I mean one passing in a series of spark between the conductor of the machine and the apparatus: by a continuous current one that passes through metallic conductors, and in that respect without interruption at the same place.

1552. Hence I conclude that dark disruptive discharge may occur (1547. 1550.); and also, that, in the luminous brush, the visible ramifications may not show the full extent of the disruptive discharge (1444. 1452.), but that each may have a dark outside, enveloping, as it were, every part through which the discharge extends. It is probable, even, that there are such things as dark discharges analogous in form to the brush and the spark, but not luminous in any part (1445.).

1553. The occurrence of dark discharge in any case shows at how low a tension disruptive discharge may occur (1548,), and indicates that the light of the ultimate brush or spark is in no relation to the intensity required (1368. 1370.). So to speak, the discharge begins in darkness, and the light is a mere consequence of the quantity which, after discharge has commenced, flows to that spot and there finds its most facile passage (1418. 1435.). As an illustration of the growth generally of discharge, I may remark that, in the experiments on the transition in oxygen of the discharge from spark to brush (1518.), every spark was immediately preceded by a short brush.

1554. The phenomena relative to dark discharge in other gases, though differing in certain characters from those in air, confirm the conclusions drawn above. The two rounded terminations (1544.) (fig. 133.), were placed in muriatic acid gas (1445. 1463.) at the pressure of 6.5 inches of mercury, and a continuous machine current of electricity sent through the apparatus: bright sparks occurred until the interval was about or above an inch, when they were replaced by squat brushy intermitting glows upon both terminations, with a dark part between. When the current at the machine was in spark, then each spark caused a discharge across the muriatic acid gas, which, with a certain interval, was bright; with a larger interval, was straight across and flamy, like a very exhausted and sudden, but not a dense sharp spark; and with a still larger interval, produced a feeble brush on the inductric positive end, and a glow on the inducteous negative end, the dark part being between (1544.); and at such times, the spark at the conductor, instead of being sudden and sonorous, was dull and quiet (334.).

1555. On introducing more muriatic acid gas, until the pressure was 29.97 inches, the same terminations gave bright sparks within at small distances; but when they were about an inch or more apart, the discharge was generally with very small brushes and glow, and frequently with no light at all, though electricity had passed through the gas. Whenever the bright spark did pass through the muriatic acid gas at this pressure, it was bright throughout, presenting no dark or dull space.

1556. In coal gas, at common pressures, when the distance was about an inch, the discharge was accompanied by short brushes on the ends, and a dark interval of half an inch or more between them, notwithstanding the discharge had the sharp quick sound of a dull spark, and could not have depended in the dark part on convection (1562.).

1557. This gas presents several curious points in relation to the bright and dark parts of spark discharge. When bright sparks passed between the rod ends 0.3 of an inch in diameter (1544.), very sudden dark parts would occur next to the brightest portions of the spark. Again with these ends and also with balls (1422.), the bright sparks would be sometimes red, sometimes green, and occasionally green and red in different parts of the same spark. Again, in the experiments described (1518.), at certain intervals a very peculiar pale, dull, yet sudden discharge would pass, which, though apparently weak, was very direct in its course, and accompanied by a sharp snapping noise, as if quick in its occurrence.

1558. Hydrogen frequently gave peculiar sparks, one part being bright red, whilst the other was a dull pale gray, or else the whole spark was dull and peculiar.

1559. Nitrogen presents a very remarkable discharge, between two balls of the respective diameters of 0.15 and 2 inches (1506. 1518.), the smaller one being rendered negative either directly inducteously. The peculiar discharge occurs at intervals between 0.42 and 0.68, and even at 1.4 inches when the large ball was inductric positively; it consisted of a little brushy part on the small negative ball, then a dark space, and lastly a dull straight line on the large positive ball (fig. 134.). The position of the dark space was very constant, and is probably in direct relation to the dark space described when negative glow was produced (1544.). When by any circumstance a bright spark was determined, the contrast with the peculiar spark described was very striking; for it always had a faint purple part, but the place of this part was constantly near the positive ball.

1560. Thus dark discharge appears to be decidedly established. But its establishment is accompanied by proofs that it occurs in different degrees and modes in different gases. Hence then another specific action, added to the many (1296. 1398. 1399. 1423. 1454. 1503.) by which the electrical relations of insulating dielectrics are distinguished and established, and another argument in favour of that molecular theory of induction, which is at present under examination[A].

[A] I cannot resist referring here by a note to Biot's philosophical view of the nature of the light of the electric discharge, Annales de Chimie, liii. p. 321.

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1561. What I have had to say regarding disruptive discharge has extended to some length, but I hope will be excused in consequence of the importance of the subject. Before concluding my remarks, I will again intimate in the form of a query, whether we have not reason to consider the tension or retention and after discharge in air or other insulating dielectrics, as the same thing with retardation and discharge in a metal wire, differing only, but almost infinitely, in degree (1334. 1336.). In other words, can we not, by a gradual chain of association, carry up discharge from its occurrence in air, through spermaceti and water, to solutions, and then on to chlorides, oxides and metals, without any essential change in its character; and, at the same time, connecting the insensible conduction of air, through muriatic acid gas and the dark discharge, with the better conduction of spermaceti, water, and the all but perfect conduction of the metals, associate the phenomena at both extremes? and may it not be, that the retardation and ignition of a wire are effects exactly correspondent in their nature to the retention of charge and spark in air? If so, here again the two extremes in property amongst dielectrics will be found to be in intimate relation, the whole difference probably depending upon the mode and degree in which their particles polarize under the influence of inductive actions (1338. 1603. 1610.).

* * * * *

P x. Convection, or carrying discharge.

1562. The last kind of discharge which I have to consider is that effected by the motion of charged particles from place to place. It is apparently very different in its nature to any of the former modes of discharge (1319.), but, as the result is the same, may be of great importance in illustrating, not merely the nature of discharge itself, but also of what we call the electric current. It often, as before observed, in cases of brush and glow (1440. 1535.), joins its effect to that of disruptive discharge, to complete the act of neutralization amongst the electric forces.

1563. The particles which being charged, then travel, may be either of insulating or conducting matter, large or small. The consideration in the first place of a large particle of conducting matter may perhaps help our conceptions.

1564. A copper boiler 3 feet in diameter was insulated and electrified, but so feebly, that dissipation by brushes or disruptive discharge did not occur at its edges or projecting parts in a sensible degree. A brass ball, 2 inches in diameter, suspended by a clean white silk thread, was brought towards it, and it was found that, if the ball was held for a second or two near any part of the charged surface of the boiler, at such distance (two inches more or less) as not to receive any direct charge from it, it became itself charged, although insulated the whole time; and its electricity was the reverse of that of the boiler.

1565. This effect was the strongest opposite the edges and projecting parts of the boiler, and weaker opposite the sides, or those extended portions of the surface which, according to Coulomb's results, have the weakest charge. It was very strong opposite a rod projecting a little way from the boiler. It occurred when the copper was charged negatively as well as positively: it was produced also with small balls down to 0.2 of an inch and less in diameter, and also with smaller charged conductors than the copper. It is, indeed, hardly possible in some cases to carry an insulated ball within an inch or two of a charged plane or convex surface without its receiving a charge of the contrary kind to that of the surface.

1566. This effect is one of induction between the bodies, not of communication. The ball, when related to the positive charged surface by the intervening dielectric, has its opposite sides brought into contrary states, that side towards the boiler being negative and the outer side positive. More inductric action is directed towards it than would have passed across the same place if the ball had not been there, for several reasons; amongst others, because, being a conductor, the resistance of the particles of the dielectric, which otherwise would have been there, is removed (1298.); and also, because the reacting positive surface of the ball being projected further out from the boiler than when there is no introduction of conducting matter, is more free therefore to act through the rest of the dielectric towards surrounding conductors, and so favours the exaltation of that inductric polarity which is directed in its course. It is, as to the exaltation of force upon its outer surface beyond that upon the inductric surface of the boiler, as if the latter were itself protuberant in that direction. Thus it acquires a state like, but higher than, that of the surface of the boiler which causes it; and sufficiently exalted to discharge at its positive surface to the air, or to affect small particles, as it is itself affected by the boiler, and they flying to it, take a charge and pass off; and so the ball, as a whole, is brought into the contrary inducteous state. The consequence is, that, if free to move, its tendency, under the influence of all the forces, to approach the boiler is increased, whilst it at the same time becomes more and more exalted in its condition, both of polarity and charge, until, at a certain distance, discharge takes place, it acquires the same state as the boiler, is repelled, and passing to that conductor most favourably circumstanced to discharge it, there resumes its first indifferent condition.

1567. It seems to me, that the manner in which inductric bodies affect uncharged floating or moveable conductors near them, is very frequently of this nature, and generally so when it ends in a carrying operation (1562. 1602.). The manner in which, whilst the dominant inductric body cannot give off its electricity to the air, the inducteous body can effect the discharge of the same kind of force, is curious, and, in the case of elongated or irregularly shaped conductors, such as filaments or particles of dust, the effect will often be very ready, and the consequent attraction immediate.

1568. The effect described is also probably influential in causing those variations in spark discharge referred to in the last series (1386. 1390. 1391.): for if a particle of dust were drawn towards the axis of induction between the balls, it would tend, whilst at some distance from that axis, to commence discharge at itself, in the manner described (1566.), and that commencement might so far facilitate the act (1417. 1420.) as to make the complete discharge, as spark, pass through the particle, though it might not be the shortest course from ball to ball. So also, with equal balls at equal distances, as in the experiments of comparison already described (1493. 1506.), a particle being between one pair of balls would cause discharge there in preference; or even if a particle were between each, difference of size or shape would give one for the time a predominance over the other.

1569. The power of particles of dust to carry off electricity in cases of high tension is well known, and I have already mentioned some instances of the kind in the use of the inductive apparatus (1201.). The general operation is very well shown by large light objects, as the toy called the electrical spider; or, if smaller ones are wanted for philosophical investigation, by the smoke of a glowing green wax taper, which, presenting a successive stream of such particles, makes their course visible.

1570. On using oil of turpentine as the dielectric, the action and course of small conducting carrying particles in it can be well observed. A few short pieces of thread will supply the place of carriers, and their progressive action is exceedingly interesting.

1571. A very striking effect was produced on oil of turpentine, which, whether it was due to the carrying power of the particles in it, or to any other action of them, is perhaps as yet doubtful. A portion of that fluid in a glass vessel had a large uninsulated silver dish at the bottom, and an electrified metal rod with a round termination dipping into it at the top. The insulation was very good, and the attraction and other phenomena striking. The rod end, with a drop of gum water attached to it, was then electrified in the fluid; the gum water soon spun off in fine threads, and was quickly dissipated through the oil of turpentine. By the time that four drops had in this way been commingled with a pint of the dielectric, the latter had lost by far the greatest portion of its insulating power; no sparks could be obtained in the fluid; and all the phenomena dependent upon insulation had sunk to a low degree. The fluid was very slightly turbid. Upon being filtered through paper only, it resumed its first clearness, and now insulated as well as before. The water, therefore, was merely diffused through the oil of turpentine, not combined with or dissolved in it: but whether the minute particles acted as carriers, or whether they were not rather gathered together in the line of highest inductive tension (1350.), and there, being drawn into elongated forms by the electric forces, combined their effects to produce a band of matter having considerable conducting power, as compared with the oil of turpentine, is as yet questionable.

1572. The analogy between the action of solid conducting carrying particles and that of the charged particles of fluid insulating substances, acting as dielectrics, is very evident and simple; but in the latter case the result is, necessarily, currents in the mobile media. Particles are brought by inductric action into a polar state; and the latter, after rising to a certain tension (1370.), is followed by the communication of a part of the force originally on the conductor; the particles consequently become charged, and then, under the joint influence of the repellent and attractive forces, are urged towards a discharging place, or to that spot where these inductric forces are most easily compensated by the contrary inducteous forces.

1573. Why a point should be so exceedingly favourable to the production of currents in a fluid insulating dielectric, as air, is very evident. It is at the extremity of the point that the intensity necessary to charge the air is first acquired (1374.); it is from thence that the charged particle recedes; and the mechanical force which it impresses on the air to form a current is in every way favoured by the shape and position of the rod, of which the point forms the termination. At the same time, the point, having become the origin of an active mechanical force, does, by the very act of causing that force, namely, by discharge, prevent any other part of the rod from acquiring the same necessary condition, and so preserves and sustains its own predominance.

1574. The very varied and beautiful phenomena produced by sheltering or enclosing the point, illustrate the production of the current exceedingly well, and justify the same conclusions; it being remembered that in such cases the effect upon the discharge is of two kinds. For the current may be interfered with by stopping the access of fresh uncharged air, or retarding the removal of that which has been charged, as when a point is electrified in a tube of insulating matter closed at one extremity; or the electric condition of the point itself may be altered by the relation of other parts in its neighbourhood, also rendered electric, as when the point is in a metal tube, by the metal itself, or when it is in the glass tube, by a similar action of the charged parts of the glass, or even by the surrounding air which has been charged, and which cannot escape.

1575. Whenever it is intended to observe such inductive phenomena in a fluid dielectric as have a direct relation to, and dependence upon, the fluidity of the medium, such, for instance, as discharge from points, or attractions and repulsions, &c., then the mass of the fluid should be great, and in such proportion to the distance between the inductric and inducteous surfaces as to include all the lines of inductive force (1369.) between them; otherwise, the effects of currents, attraction, &c., which are the resultants of all these forces, cannot be obtained. The phenomena, which occur in the open air, or in the middle of a globe filled with oil of turpentine, will not take place in the same media if confined in tubes of glass, shell-lac, sulphur, or other such substances, though they be excellent insulating dielectrics; nor can they be expected: for in such cases, the polar forces, instead of being all dispersed amongst fluid particles, which tend to move under their influence, are now associated in many parts with particles that, notwithstanding their tendency to motion, are constrained by their solidity to remain quiescent.

1576. The varied circumstances under which, with conductors differently formed and constituted, currents can occur, all illustrate the same simplicity of production. A ball, if the intensity be raised sufficiently on its surface, and that intensity be greatest on a part consistent with the production of a current of air up to and off from it, will produce the effect like a point (1537); such is the case whenever the glow occurs upon a ball, the current being essential to that phenomenon. If as large a sphere as can well be employed with the production of glow be used, the glow will appear at the place where the current leaves the ball, and that will be the part directly opposite to the connection of the ball and rod which supports it; but by increasing the tension elsewhere, so as to raise it above the tension upon that spot, which can easily be effected inductively, then the place of the glow and the direction of the current will also change, and pass to that spot which for the time is most favourable for their production (1591.).

1577. For instance, approaching the hand towards the ball will tend to cause brush (1539.), but by increasing the supply of electricity the condition of glow may be preserved; then on moving the hand about from side to side the position of the glow will very evidently move with it.

1578. A point brought towards a glowing ball would at twelve or fourteen inches distance make the glow break into brush, but when still nearer, glow was reproduced, probably dependent upon the discharge of wind or air passing from the point to the ball, and this glow was very obedient to the motion of the point, following it in every direction.

1579. Even a current of wind could affect the place of the glow; for a varnished glass tube being directed sideways towards the ball, air was sometimes blown through it at the ball and sometimes not. In the former case, the place of the glow was changed a little, as if it were blown away by the current, and this is just the result which might have been anticipated. All these effects illustrate beautifully the general causes and relations, both of the glow and the current of air accompanying it (1574.).

1580. Flame facilitates the production of a current in the dielectric surrounding it. Thus, if a ball which would not occasion a current in the air have a flame, whether large or small, formed on its surface, the current is produced with the greatest ease; but not the least difficulty can occur in comprehending the effective action of the flame in this case, if its relation, as part of the surrounding dielectric, to the electrified ball, be but for a moment considered (1375. 1380.).

1581. Conducting fluid terminations, instead of rigid points, illustrate in a very beautiful manner the formation of the currents, with their effects and influence in exalting the conditions under which they were commenced. Let the rounded end of a brass rod, 0.3 of an inch or thereabouts in diameter, point downwards in free air; let it be amalgamated, and have a drop of mercury suspended from it; and then let it be powerfully electrized. The mercury will present the phenomenon of glow; a current of air will rush along the rod, and set off from the mercury directly downwards; and the form of the metallic drop will be slightly affected, the convexity at a small part near the middle and lower part becoming greater, whilst it diminishes all round at places a little removed from this spot. The change is from the form of a (fig. 135.) to that of b, and is due almost, if not entirely, to the mechanical force of the current of air sweeping over its surface.

1582. As a comparative observation, let it be noticed, that a ball gradually brought towards it converts the glow into brushes, and ultimately sparks pass from the most projecting part of the mercury. A point does the same, but at much smaller distances.

1583. Take next a drop of strong solution of muriate of lime; being electrified, a part will probably be dissipated, but a considerable portion, if the electricity be not too powerful, will remain, forming a conical drop (fig. 136.), accompanied by a strong current. If glow be produced, the drop will be smooth on the surface. If a short low brush is formed, a minute tremulous motion of the liquid will be visible; but both effects coincide with the principal one to be observed, namely, the regular and successive charge of air, the formation of a wind or current, and the form given by that current to the fluid drop, if a discharge ball be gradually brought toward the cone, sparks will at last pass, and these will be from the apex of the cone to the approached ball, indicating a considerable degree of conducting power in this fluid.

1584. With a drop of water, the effects were of the same kind, and were best obtained when a portion of gum water or of syrup hung from a ball (fig. 137.). When the machine was worked slowly, a fine large quiet conical drop, with concave lateral outline, and a small rounded end, was produced, on which the glow appeared, whilst a steady wind issued, in a direction from the point of the cone, of sufficient force to depress the surface of uninsulated water held opposite to the termination. When the machine was worked more rapidly some of the water was driven off; the smaller pointed portion left was roughish on the surface, and the sound of successive brush discharges was heard. With still more electricity, more water was dispersed; that which remained was elongated and contracted, with an alternating motion; a stronger brush discharge was heard, and the vibrations of the water and the successive discharges of the individual brushes were simultaneous. When water from beneath was brought towards the drop, it did not indicate the same regular strong contracted current of air as before; and when the distance was such that sparks passed, the water beneath was attracted rather than driven away, and the current of air ceased.

1585. When the discharging ball was brought near the drop in its first quiet glowing state (1582.), it converted that glow into brushes, and caused the vibrating motion of the drop. When still nearer, sparks passed, but they were always from the metal of the rod, over the surface of the water, to the point, and then across the air to the ball. This is a natural consequence of the deficient conducting power of the fluid (1584. 1585.).

1586. Why the drop vibrated, changing its form between the periods of discharging brushes, so as to be more or less acute at particular instants, to be most acute when the brush issued forth, and to be isochronous in its action, and how the quiet glowing liquid drop, on assuming the conical form, facilitated, as it were, the first action, are points, as to theory, so evident, that I will not stop to speak of them. The principal thing to observe at present is, the formation of the carrying current of air, and the manner in which it exhibits its existence and influence by giving form to the drop.

1587. That the drop, when of water, or a better conductor than water, is formed into a cone principally by the current of air, is shown amongst other ways (1594.) thus. A sharp point being held opposite the conical drop, the latter soon lost its pointed form; was retraced and became round; the current of air from it ceased, and was replaced by one from the point beneath, which, if the latter were held near enough to the drop, actually blew it aside, and rendered it concave in form.

1588. It is hardly necessary to say what happened with still worse conductors than water, as oil, or oil of turpentine; the fluid itself was then spun out into threads and carried off, not only because the air rushing over its surface helped to sweep it away, but also because its insulating particles assumed the same charged state as the particles of air, and, not being able to discharge to them in a much greater decree than the air particles themselves could do, were carried off by the same causes which urged those in their course. A similar effect with melted sealing-wax on a metal point forms an old and well-known experiment.

1589. A drop of gum water in the exhausted receiver of the air-pump was not sensibly affected in its form when electrified. When air was let in, it begun to show change of shape when the pressure was ten inches of mercury. At the pressure of fourteen or fifteen inches the change was more sensible, and as the air increased in density the effects increased, until they were the same as those in the open atmosphere. The diminished effect in the rare air I refer to the relative diminished energy of its current; that diminution depending, in the first place, on the lower electric condition of the electrified ball in the rarefied medium, and in the next, on the attenuated condition of the dielectric, the cohesive force of water in relation to rarefied air being something like that of mercury to dense air (1581.), whilst that of water in dense air may be compared to that of mercury in oil of turpentine (1597.).

1590. When a ball is covered with a thick conducting fluid, as treacle or syrup, it is easy by inductive action to determine the wind from almost any part of it (1577.); the experiment, which before was of rather difficult performance, being rendered facile in consequence of the fluid enabling that part, which at first was feeble in its action, to rise into an exalted condition by assuming a pointed form.

1591. To produce the current, the electric intensity must rise and continue at one spot, namely, at the origin of the current, higher than elsewhere, and then, air having a uniform and ready access, the current is produced. If no current be allowed (1574.), then discharge may take place by brush or spark. But whether it be by brush or spark, or wind, it seems very probable that the initial intensity or tension at which a particle of a given gaseous dielectric charges, or commences discharge, is, under the conditions before expressed, always the same (1410.).

1592. It is not supposed that all the air which enters into motion is electrified; on the contrary, much that is not charged is carried on into the stream. The part which is really charged may be but a small proportion of that which is ultimately set in motion (1442.).

1593. When a drop of gum water (1584.) is made negative, it presents a larger cone than when made positive; less of the fluid is thrown off, and yet, when a ball is approached, sparks can hardly be obtained, so pointed is the cone, and so free the discharge. A point held opposite to it did not cause the retraction of the cone to such an extent as when it was positive. All the effects are so different from those presented by the positive cone, that I have no doubt such drops would present a very instructive method of investigating the difference of positive and negative discharge in air and other dielectrics (1480. 1501.).

1594. That I may not be misunderstood (1587.), I must observe here that I do not consider the cones produced as the result only of the current of air or other insulating dielectric over their surface. When the drop is of badly conducting matter, a part of the effect is due to the electrified state of the particles, and this part constitutes almost the whole when the matter is melted sealing-wax, oil of turpentine, and similar insulating bodies (1588.). But even when the drop is of good conducting matter, as water, solutions, or mercury, though the effect above spoken of will then be insensible (1607.), still it is not the mere current of air or other dielectric which produces all the change of form; for a part is due to those attractive forces by which the charged drop, if free to move, would travel along the line of strongest induction, and not being free to move, has its form elongated until the sum of the different forces tending to produce this form is balanced by the cohesive attraction of the fluid. The effect of the attractive forces are well shown when treacle, gum water, or syrup is used; for the long threads which spin out, at the same time that they form the axes of the currents of air, which may still be considered as determined at their points, are like flexible conductors, and show by their directions in what way the attractive forces draw them.

1595. When the phenomena of currents are observed in dense insulating dielectrics, they present us with extraordinary degrees of mechanical force. Thus, if a pint of well-rectified and filtered (1571.) oil of turpentine be put into a glass vessel, and two wires be dipped into it in different places, one leading to the electrical machine, and the other to the discharging train, on working the machine the fluid will be thrown into violent motion throughout its whole mass, whilst at the same time it will rise two, three or four inches up the machine wire, and dart off jets from it into the air.

1596. If very clean uninsulated mercury be at the bottom of the fluid, and the wire from the machine be terminated either by a ball or a point, and also pass through a glass tube extending both above and below the surface of the oil of turpentine, the currents can be better observed, and will be seen to rush down the wire, proceeding directly from it towards the mercury, and there, diverging in all directions, will ripple its surface strongly, and mounting up at the sides of the vessel, will return to re-enter upon their course.

1597. A drop of mercury being suspended from an amalgamated brass ball, preserved its form almost unchanged in air (1581.); but when immersed in the oil of turpentine it became very pointed, and even particles of the metal could be spun out and carried off by the currents of the dielectric. The form of the liquid metal was just like that of the syrup in air (1584.), the point of the cone being quite as fine, though not so long. By bringing a sharp uninsulated point towards it, it could also be effected in the same manner as the syrup drop in air (1587.), though not so readily, because of the density and limited quantity of the dielectric.

1598. If the mercury at the bottom of the fluid be connected with the electrical machine, whilst a rod is held in the hand terminating in a ball three quarters of an inch, less or more, in diameter, and the ball be dipped into the electrified fluid, very striking appearances ensue. When the ball is raised again so as to be at a level nearly out of the fluid, large portions of the latter will seem to cling to it (fig. 138.). If it be raised higher, a column of the oil of turpentine will still connect it with that in the basin below (fig. 139.). If the machine be excited into more powerful action, this will become more bulky, and may then also be raised higher, assuming the form (fig. 140); and all the time that these effects continue, currents and counter-currents, sometimes running very close together, may be observed in the raised column of fluid.

1599. It is very difficult to decide by sight the direction of the currents in such experiments as these. If particles of silk are introduced they cling about the conductors; but using drops of water and mercury the course of the fluid dielectric seems well indicated. Thus, if a drop of water be placed at the end of a rod (1571.) over the uninsulated mercury, it is soon swept away in particles streaming downwards towards the mercury. If another drop be placed on the mercury beneath the end of the rod, it is quickly dispersed in all directions in the form of streaming particles, the attractive forces drawing it into elongated portions, and the currents carrying them away. If a drop of mercury be hung from a ball used to raise a column of the fluid (1598.), then the shape of the drop seems to show currents travelling in the fluid in the direction indicated by the arrows (fig. 141.).

1600. A very remarkable effect is produced on these phenomena, connected with positive and negative charge and discharge, namely, that a ball charged positively raises a much higher and larger column of the oil of turpentine than when charged negatively. There can be no doubt that this is connected with the difference of positive and negative action already spoken of (1480. 1525.), and tends much to strengthen the idea that such difference is referable to the particles of the dielectric rather than to the charged conductors, and is dependent upon the mode in which these particles polarize (1503. 1523.).

1601. Whenever currents travel in insulating dielectrics they really effect discharge; and it is important to observe, though a very natural result, that it is indifferent which way the current or particles travel, as with reversed direction their state is reversed. The change is easily made, either in air or oil of turpentine, between two opposed rods, for an insulated ball being placed in connexion with either rod and brought near its extremity, will cause the current to set towards it from the opposite end.

1602. The two currents often occur at once, as when both terminations present brushes, and frequently when they exhibit the glow (1531.). In such cases, the charged particles, or many of them, meet and mutually discharge each other (1518. 1612.). If a smoking wax taper be held at the end of an insulating rod towards a charged prime conductor, it will very often happen that two currents will form, and be rendered visible by its vapour, one passing as a fine filament of smoky particles directly to the charged conductor, and the other passing as directly from the same taper wick outwards, and from the conductor: the principles of inductric action and charge, which were referred to in considering the relation of a carrier ball and a conductor (1566.), being here also called into play.

* * * * *

1603. The general analogy and, I think I may say, identity of action found to exist as to insulation and conduction (1338. 1561.) when bodies, the best and the worst in the classes of insulators or conductors, were compared, led me to believe that the phenomena of convection in badly conducting media were not without their parallel amongst the best conductors, such even as the metals. Upon consideration, the cones produced by Davy[A] in fluid metals, as mercury and tin, seemed to be cases in point, and probably also the elongation of the metallic medium through which a current of electricity was passing, described by Ampere (1113)[B]; for it is not difficult to conceive, that the diminution of convective effect, consequent upon the high conducting power of the metallic media used in these experiments, might be fully compensated for by the enormous quantity of electricity passing. In fact, it is impossible not to expect some effect, whether sensible or not, of the kind in question, when such a current is passing through a fluid offering a sensible resistance to the passage of the electricity, and, thereby, giving proof of a certain degree of insulating power (1328.).

[A] Philosophical Transactions, 1823, p. 155.

[B] Bibliotheque Universelle, xxi, 417.

1604. I endeavoured to connect the convective currents in air, oil of turpentine, &c. and those in metals, by intermediate cases, but found this not easy to do. On taking bodies, for instance, which, like water, adds, solutions, fused salts or chlorides, &c., have intermediate conducting powers, the minute quantity of electricity which the common machine can supply (371. 861.) is exhausted instantly, so that the cause of the phenomenon is kept either very low in intensity, or the instant of time during which the effect lasts is so small, that one cannot hope to observe the result sought for. If a voltaic battery be used, these bodies are all electrolytes, and the evolution of gas, or the production of other changes, interferes and prevents observation of the effect required.

1605. There are, nevertheless, some experiments which illustrate the connection. Two platina wires, forming the electrodes of a powerful voltaic battery, were placed side by side, near each other, in distilled water, hermetically sealed up in a strong glass tube, some minute vegetable fibres being present in the water. When, from the evolution of gas and the consequent increased pressure, the bubbles formed on the electrodes were so small as to produce but feebly ascending currents, then it could be observed that the filaments present were attracted and repelled between the two wires, as they would have been between two oppositely charged surfaces in air or oil of turpentine, moving so quickly as to displace and disturb the bubbles and the currents which these tended to form. Now I think it cannot be doubted, that under similar circumstances, and with an abundant supply of electricity, of sufficient tension also, convective currents might have been formed; the attractions and repulsions of the filaments were, in fact, the elements of such currents (1572.), and therefore water, though almost infinitely above air or oil of turpentine as a conductor, is a medium in which similar currents can take place.

1606. I had an apparatus made (fig. 142.) in which a is a plate of shell-lac, b a fine platina wire passing through it, and having only the section of the wire exposed above; c a ring of bibulous paper resting on the shell-lac, and d distilled water retained by the paper in its place, and just sufficient in quantity to cover the end of the wire b; another wire, e, touched a piece of tinfoil lying in the water, and was also connected with a discharging train; in this way it was easy, by rendering b either positive or negative, to send a current of electricity by its extremity into the fluid, and so away by the wire e.

1607. On connecting b with the conductor of a powerful electrical machine, not the least disturbance of the level of the fluid over the end of the wire during the working of the machine could be observed; but at the same time there was not the smallest indication of electrical charge about the conductor of the machine, so complete was the discharge. I conclude that the quantity of electricity passed in a given time had been too small, when compared with the conducting power of the fluid to produce the desired effect.

1608. I then charged a large Leyden battery (291.), and discharged it through the wire b, interposing, however, a wet thread, two feet long, to prevent a spark in the water, and to reduce what would else have been a sudden violent discharge into one of more moderate character, enduring for a sensible length of time (334.). I now did obtain a very brief elevation of the water over the end of the wire; and though a few minute bubbles of gas were at the same time formed there, so as to prevent me from asserting that the effect was unequivocally the same as that obtained by DAVY in the metals, yet, according to my best judgement, it was partly, and I believe principally, of that nature.

1609. I employed a voltaic battery of 100 pair of four-inch plates for experiments of a similar nature with electrolytes. In these cases the shell-lac was cupped, and the wire b 0.2 of an inch in diameter. Sometimes I used a positive amalgamated zinc wire in contact with dilute sulphuric acid; at others, a negative copper wire in a solution of sulphate of copper; but, because of the evolution of gas, the precipitation of copper, &c., I was not able to obtain decided results. It is but right to mention, that when I made use of mercury, endeavouring to repeat DAVY's experiment, the battery of 100 pair was not sufficient to produce the elevations[A].

[A] In the experiments at the Royal Institution, Sir H. Davy used, I think, 500 or 600 pairs of plates. Those at the London Institution were made with the apparatus of Mr. Pepys (consisting of an enormous single pair of plates), described in the Philosophical Transactions for 1832, p. 187.

1610. The latter experiments (1609.) may therefore be considered as failing to give the hoped-for proof, but I have much confidence in the former (1605. 1608.), and in the considerations (1603.) connected with them. If I have rightly viewed them, and we may be allowed to compare the currents at points and surfaces in such extremely different bodies as air and the metals, and admit that they are effects of the same kind, differing only in degree and in proportion to the insulating or conducting power of the dielectric used, what great additional argument we obtain in favour of that theory, which in the phenomena of insulation and conduction also, as in these, would link the same apparently dissimilar substances together (1336. 1561.); and how completely the general view, which refers all the phenomena to the direct action of the molecules of matter, seems to embrace the various isolated phenomena as they successively come under consideration!

* * * * *

1611. The connection of this convective or carrying effect, which depends upon a certain degree of insulation, with conduction; i.e. the occurrence of both in so many of the substances referred to, as, for instance, the metals, water, air, &c., would lead to many very curious theoretical generalizations, which I must not indulge in here. One point, however, I shall venture to refer to. Conduction appears to be essentially an action of contiguous particles, and the considerations just stated, together with others formerly expressed (1326, 1336, &c.), lead to the conclusion, that all bodies conduct, and by the same process, air as well as metals; the only difference being in the necessary degree of force or tension between the particles which must exist before the act of conduction or transfer from one particle to another can take place.

1612. The question then arises, what is this limiting condition which separates, as it were, conduction and insulation from each other? Does it consist in a difference between the two contiguous particles, or the contiguous poles of these particles, in the nature and amount of positive and negative force, no communication or discharge occurring unless that difference rises up to a certain degree, variable for different bodies, but always the same for the same body? Or is it true that, however small the difference between two such particles, if time be allowed, equalization of force will take place, even with the particles of such bodies as air, sulphur or lac? In the first case, insulating power in any particular body would be proportionate to the degree of the assumed necessary difference of force; in the second, to the time required to equalize equal degrees of difference in different bodies. With regard to airs, one is almost led to expect a permanent difference of force; but in all other bodies, time seems to be quite sufficient to ensure, ultimately, complete conduction. The difference in the modes by which insulation may be sustained, or conduction effected, is not a mere fanciful point, but one of great importance, as being essentially connected with the molecular theory of induction, and the manner in which the particles of bodies assume and retain their polarized state.

* * * * *

P xi. Relation of a vacuum to electrical phenomena.

1613. It would seem strange, if a theory which refers all the phenomena of insulation and conduction, i.e. all electrical phenomena, to the action of contiguous particles, were to omit to notice the assumed possible case of a vacuum. Admitting that a vacuum can be produced, it would be a very curious matter indeed to know what its relation to electrical phenomena would be; and as shell-lac and metal are directly opposed to each other, whether a vacuum would be opposed to them both, and allow neither of induction or conduction across it. Mr. Morgan[A] has said that a vacuum does not conduct. Sir H. Davy concluded from his investigations, that as perfect a vacuum as could be made[B] did conduct, but does not consider the prepared spaces which he used as absolute vacua. In such experiments I think I have observed the luminous discharge to be principally on the inner surface of the glass; and it does not appear at all unlikely, that, if the vacuum refused to conduct, still the surface of glass next it might carry on that action.

[A] Philosophical Transactions, 1785, p. 272

[B] Ibid. 1822, p. 64.

1614. At one time, when I thought inductive force was exerted in right lines, I hoped to illustrate this important question by making experiments on induction with metallic mirrors (used only as conducting vessels) exposed towards a very clear sky at night time, and of such concavity that nothing but the firmament could be visible from the lowest part of the concave n, fig. 143. Such mirrors, when electrified, as by connexion with a Leyden jar, and examined by a carrier ball, readily gave electricity at the lowest part of their concavity if in a room; but I was in hopes of finding that, circumstanced as before stated, they would give little or none at the same spot, if the atmosphere above really terminated in a vacuum. I was disappointed in the conclusion, for I obtained as much electricity there as before; but on discovering the action of induction in curved lines (1231.), found a full and satisfactory explanation of the result.

1615. My theory, as far as I have ventured it, does not pretend to decide upon the consequences of a vacuum. It is not at present limited sufficiently, or rendered precise enough, either by experiments relating to spaces void of matter, or those of other kinds, to indicate what would happen in the vacuum case. I have only as yet endeavoured to establish, what all the facts seem to prove, that when electrical phenomena, as those of induction, conduction, insulation and discharge occur, they depend on, and are produced by the action of contiguous particles of matter, the next existing particle being considered as the contiguous one; and I have further assumed, that these particles are polarized; that each exhibits the two forces, or the force in two directions (1295. 1298.); and that they act at a distance, only by acting on the contiguous and intermediate particles.

1616. But assuming that a perfect vacuum were to intervene in the course of the lines of inductive action (1304.), it does not follow from this theory, that the particles on opposite sides of such a vacuum could not act on each other. Suppose it possible for a positively electrified particle to be in the centre of a vacuum an inch in diameter, nothing in my present views forbids that the particle should act at the distance of half an inch on all the particles forming the inner superficies of the bounding sphere, and with a force consistent with the well-known law of the squares of the distance. But suppose the sphere of an inch were full of insulating matter, the electrified particle would not then, according to my notion, act directly on the distant particles, but on those in immediate association with it, employing all its power in polarizing them; producing in them negative force equal in amount to its own positive force and directed towards the latter, and positive force of equal amount directed outwards and acting in the same manner upon the layer of particles next in succession. So that ultimately, those particles in the surface of a sphere of half an inch radius, which were acted on directly when that sphere was a vacuum, will now be acted on indirectly as respects the central particle or source of action, i.e. they will be polarized in the same way, and with the same amount of force.

S 19. Nature of the electric current.

1617. The word current is so expressive in common language, that when applied in the consideration of electrical phenomena we can hardly divest it sufficiently of its meaning, or prevent our minds from being prejudiced by it (283. 511.). I shall use it in its common electrical sense, namely, to express generally a certain condition and relation of electrical forces supposed to be in progression.

1618. A current is produced both by excitement and discharge; and whatsoever the variation of the two general causes may be, the effect remains the same. Thus excitement may occur in many ways, as by friction, chemical action, influence of heat, change of condition, induction, &c.; and discharge has the forms of conduction, electrolyzation, disruptive discharge, and convection; yet the current connected with these actions, when it occurs, appears in all cases to be the same. This constancy in the character of the current, notwithstanding the particular and great variations which may be made in the mode of its occurrence, is exceedingly striking and important; and its investigation and development promise to supply the most open and advantageous road to a true and intimate understanding of the nature of electrical forces.

1619. As yet the phenomena of the current have presented nothing in opposition to the view I have taken of the nature of induction as an action of contiguous particles. I have endeavoured to divest myself of prejudices and to look for contradictions, but I have not perceived any in conductive, electrolytic, convective, or disruptive discharge.

1620. Looking at the current as a cause, it exerts very extraordinary and diverse powers, not only in its course and on the bodies in which it exists, but collaterally, as in inductive or magnetic phenomena.

1621. Electrolytic action.--One of its direct actions is the exertion of pure chemical force, this being a result which has now been examined to a considerable extent. The effect is found to be constant and definite for the quantity of electric force discharged (783. &c.); and beyond that, the intensity required is in relation to the intensity of the affinity or forces to be overcome (904. 906. 911.). The current and its consequences are here proportionate; the one may be employed to represent the other; no part of the effect of either is lost or gained; so that the case is a strict one, and yet it is the very case which most strikingly illustrates the doctrine that induction is an action of contiguous particles (1164. 1343.).

1622. The process of electrolytic discharge appears to me to be in close analogy, and perhaps in its nature identical with another process of discharge, which at first seems very different from it, I mean convection (1347. 1572.). In the latter case the particles may travel for yards across a chamber; they may produce strong winds in the air, so as to move machinery; and in fluids, as oil of turpentine, may even shake the hand, and carry heavy metallic bodies about[A]; and yet I do not see that the force, either in kind or action, is at all different to that by which a particle of hydrogen leaves one particle of oxygen to go to another, or by which a particle of oxygen travels in the contrary direction.

[A] If a metallic vessel three or four inches deep, containing oil of turpentine, be insulated and electrified, and a rod with a ball (an inch or more in diameter) at the end have the ball immersed in the fluid whilst the end is held in the hand, the mechanical force generated when the ball is moved to and from the sides of the vessel will soon be evident to the experimenter.

1623. Travelling particles of the air can effect chemical changes just as well as the contact of a fixed platina electrode, or that of a combining electrode, or the ions of a decomposing electrolyte (453. 471.); and in the experiment formerly described, where eight places of decomposition were rendered active by one current (469.), and where charged particles of air in motion were the only electrical means of connecting these parts of the current, it seems to me that the action of the particles of the electrolyte and of the air were essentially the same. A particle of air was rendered positive; it travelled in a certain determinate direction, and coming to an electrolyte, communicated its powers; an equal amount of positive force was accordingly acquired by another particle (the hydrogen), and the latter, so charged, travelled as the former did, and in the same direction, until it came to another particle, and transferred its power and motion, making that other particle active. Now, though the particle of air travelled over a visible and occasionally a large space, whilst the particle of the electrolyte moved over an exceedingly small one; though the air particle might be oxygen, nitrogen, or hydrogen, receiving its charge from force of high intensity, whilst the electrolytic particle of hydrogen had a natural aptness to receive the positive condition with extreme facility; though the air particle might be charged with very little electricity at a very high intensity by one process, whilst the hydrogen particle might be charged with much electricity at a very low intensity by another process; these are not differences of kind, as relates to the final discharging action of these particles, but only of degree; not essential differences which make things unlike, but such differences as give to things, similar in their nature, that great variety which fits them for their office in the system of the universe.

1624. So when a particle of air, or of dust in it, electrified at a negative point, moves on through the influence of the inductive forces (1572.) to the next positive surface, and after discharge passes away, it seems to me to represent exactly that particle of oxygen which, having been rendered negative in the electrolyte, is urged by the same disposition of inductive forces, and going to the positive platina electrode, is there discharged, and then passes away, as the air or dust did before it.

1625. Heat is another direct effect of the current upon substances in which it occurs, and it becomes a very important question, as to the relation of the electric and heating forces, whether the latter is always definite in amount[A]. There are many cases, even amongst bodies which conduct without change, that at present are irreconcileable with the assumption that it is[B]; but there are also many which indicate that, when proper limitations are applied, the heat produced is definite. Harris has shown this for a given length of current in a metallic wire, using common electricity[C]; and De la Rive has proved the same point for voltaic electricity by his beautiful application of Breguet's thermometer[D].

[A] See De la Rive's Researches, Bib. Universelle, 1829, xl. p. 40.

[B] Amongst others, Davy, Philosophical Transactions, 1821, p. 438. Pelletier's important results, Annales de Chimie, 1834, lvi. p. 371. and Becquerel's non-heating current, Bib. Universelle, 1835, lx. 218.

[C] Philosophical Transactions, 1824, pp. 225. 228.

[D] Annales de Chimie, 1836, lxii. 177.

1626. When the production of heat is observed in electrolytes under decomposition, the results are still more complicated. But important steps have been taken in the investigation of this branch of the subject by De la Rive[A] and others; and it is more than probable that, when the right limitations are applied, constant and definite results will here also be obtained.

[A] Bib. Universelle, 1829, xl. 49; and Ritchie, Phil. Trans. 1832. p. 296.

* * * * *

1627. It is a most important part of the character of the current, and essentially connected with its very nature, that it is always the same. The two forces are everywhere in it. There is never one current of force or one fluid only. Any one part of the current may, as respects the presence of the two forces there, be considered as precisely the same with any other part; and the numerous experiments which imply their possible separation, as well as the theoretical expressions which, being used daily, assume it, are, I think, in contradiction with facts (511, &c.). It appears to me to be as impossible to assume a current of positive or a current of negative force alone, or of the two at once with any predominance of one over the other, as it is to give an absolute charge to matter (516. 1169. 1177.).

1628. The establishment of this truth, if, as I think, it be a truth, or on the other hand the disproof of it, is of the greatest consequence. If, as a first principle, we can establish, that the centres of the two forces, or elements of force, never can be separated to any sensible distance, or at all events not further than the space between two contiguous particles (1615.), or if we can establish the contrary conclusion, how much more clear is our view of what lies before us, and how much less embarrassed the ground over which we have to pass in attaining to it, than if we remain halting between two opinions! And if, with that feeling, we rigidly test every experiment which bears upon the point, as far as our prejudices will let us (1161.), instead of permitting them with a theoretical expression to pass too easily away, are we not much more likely to attain the real truth, and from that proceed with safety to what is at present unknown?

1629. I say these things, not, I hope, to advance a particular view, but to draw the strict attention of those who are able to investigate and judge of the matter, to what must be a turning point in the theory of electricity; to a separation of two roads, one only of which can be right: and I hope I may be allowed to go a little further into the facts which have driven me to the view I have just given.

1630. When a wire in the voltaic circuit is heated, the temperature frequently rises first, or most at one end. If this effect were due to any relation of positive or negative as respects the current, it would be exceedingly important. I therefore examined several such cases; but when, keeping the contacts of the wire and its position to neighbouring things unchanged, I altered the direction of the current, I found that the effect remained unaltered, showing that it depended, not upon the direction of the current, but on other circumstances. So there is here no evidence of a difference between one part of the circuit and another.

1631. The same point, i.e. uniformity in every part, may be illustrated by what may be considered as the inexhaustible nature of the current when producing particular effects; for these effects depend upon transfer only, and do not consume the power. Thus a current which will heat one inch of platina wire will heat a hundred inches (853. note). If a current be sustained in a constant state, it will decompose the fluid in one voltameter only, or in twenty others if they be placed in the circuit, in each to an amount equal to that in the single one.

1632. Again, in cases of disruptive discharge, as in the spark, there is frequently a dark part (1422.) which, by Professor Johnson, has been called the neutral point[A]; and this has given rise to the use of expressions implying that there are two electricities existing separately, which, passing to that spot, there combine and neutralize each other[B]. But if such expressions are understood as correctly indicating that positive electricity alone is moving between the positive ball and that spot, and negative electricity only between the negative ball and that spot, then what strange conditions these parts must be in; conditions, which to my mind are every way unlike those which really occur! In such a case, one part of a current would consist of positive electricity only, and that moving in one direction; another part would consist of negative electricity only, and that moving in the other direction; and a third part would consist of an accumulation of the two electricities, not moving in either direction, but mixing up together! and being in a relation to each other utterly unlike any relation which could be supposed to exist in the two former portions of the discharge. This does not seem to me to be natural. In a current, whatever form the discharge may take, or whatever part of the circuit or current is referred to, as much positive force as is there exerted in one direction, so much negative force is there exerted in the other. If it were not so we should have bodies electrified not merely positive and negative, but on occasions in a most extraordinary manner, one being charged with five, ten, or twenty times as much of both positive and negative electricity in equal quantities as another. At present, however, there is no known fact indicating such states.

[A] Silliman's Journal, 1834, xxv. p. 57.

[B] Thomson on Heat and Electricity, p. 171.

1633. Even in cases of convection, or carrying discharge, the statement that the current is everywhere the same must in effect be true (1627.); for how, otherwise, could the results formerly described occur? When currents of air constituted the mode of discharge between the portions of paper moistened with iodide of potassium or sulphate of soda (465. 469.), decomposition occurred; and I have since ascertained that, whether a current of positive air issued from a spot, or one of negative air passed towards it, the effect of the evolution of iodine or of acid was the same, whilst the reversed currents produced alkali. So also in the magnetic experiments (307.) whether the discharge was effected by the introduction of a wire, or the occurrence of a spark, or the passage of convective currents either one way or the other (depending on the electrified state of the particles), the result was the same, being in all cases dependent upon the perfect current.

1634. Hence, the section of a current compared with other sections of the same current must be a constant quantity, if the actions exerted be of the same kind; or if of different kinds, then the forms under which the effects are produced are equivalent to each other, and experimentally convertible at pleasure. It is in sections, therefore, we must look for identity of electrical force, even to the sections of sparks and carrying actions, as well as those of wires and electrolytes.

1635. In illustration of the utility and importance of establishing that which may be the true principle, I will refer to a few cases. The doctrine of unipolarity, as formerly stated, and I think generally understood[A], is evidently inconsistent with my view of a current (1627.); and the later singular phenomena of poles and flames described by Erman and others[B] partake of the same inconsistency of character. If a unipolar body could exist, i.e. one that could conduct the one electricity and not the other, what very new characters we should have a right to expect in the currents of single electricities passing through them, and how greatly ought they to differ, not only from the common current which is supposed to have both electricities travelling in opposite directions in equal amount at the same time, but also from each other! The facts, which are excellent, have, however, gradually been more correctly explained by Becquerel[C], Andrews[D], and others; and I understand that Professor Ohms[E] has perfected the work, in his close examination of all the phenomena; and after showing that similar phenomena can take place with good conductors, proves that with soap, &c. many of the effects are the mere consequences of the bodies evolved by electrolytic action.

[A] Erman, Annales de Chimie, 1807. lxi. p. 115. Davy's Elements, p. 168. Biot, Ency. Brit. Supp, iv. p. 444. Becquerel, Traite, i. p. 167. De la Rive, Bib. Univ. 1837. vii. 392.

[B] Erman, Annales de Chimie, 1824. xxv. 278. Becquerel, Ibid. xxxvi. p. 329

[C] Becquerel, Annales de Chimie, 1831. xlvi. p. 283.

[D] Andrews, Philosophical Magazine, 1836. ix. 182.

[E] Schweigger's Jahrbuch de Chimie, &c. 1830. Heft 8. Not understanding German, it is with extreme regret I confess I have not access, and cannot do justice, to the many most valuable papers in experimental electricity published in that language. I take this opportunity also of stating another circumstance which occasions me great trouble, and, as I find by experience, may make, me seemingly regardless of the labours of others:--it is a gradual loss of memory for some years past; and now, often when I read a memoir, I remember that I have seen it before, and would have rejoiced if at the right time I could have recollected and referred to it in the progress of my own papers.--M.F.

1636. I conclude, therefore, that the facts upon which the doctrine of unipolarity was founded are not adverse to that unity and indivisibility of character which I have stated the current to possess, any more than the phenomena of the pile itself (which might well bear comparison with those of unipolar bodies,) are opposed to it. Probably the effects which have been called effects of unipolarity, and the peculiar differences of the positive and negative surface when discharging into air, gases, or other dielectrics (1480. 1525.) which have been already referred to, may have considerable relation to each other[A].

[A] See also Hare in Silliman's Journal, 1833. xxiv. 246.

* * * * *

1637. M. de la Rive has recently described a peculiar and remarkable effect of heat on a current when passing between electrodes and a fluid[A]. It is, that if platina electrodes dip into acidulated water, no change is produced in the passing current by making the positive electrode hotter or colder; whereas making the negative electrode hotter increased the deflexion of a galvanometer affected by the current, from 12 deg. to 30 deg. and even 45 deg., whilst making it colder diminished the current in the same high proportions.

[A] Bibliotheque Universelle, 1837, vii. 388.

1638. That one electrode should have this striking relation to heat whilst the other remained absolutely without, seem to me as incompatible with what I conceived to be the character of a current as unipolarity (1627. 1635.), and it was therefore with some anxiety that I repeated the experiment. The electrodes which I used were platina; the electrolyte, water containing about one sixth of sulphuric acid by weight: the voltaic battery consisted of two pairs of amalgamated zinc and platina plates in dilute sulphuric acid, and the galvanometer in the circuit was one with two needles, and gave when the arrangement was complete a deflexion of 10 deg. or 12 deg..

1639. Under these circumstances heating either electrode increased the current; heating both produced still more effect. When both were heated, if either were cooled, the effect on the current fell in proportion. The proportion of effect due to heating this or that electrode varied, but on the whole heating the negative seemed to favour the passage of the current somewhat more than heating the positive. Whether the application of heat were by a flame applied underneath, or one directed by a blowpipe from above, or by a hot iron or coal, the effect was the same.

1640. Having thus removed the difficulty out of the way of my views regarding a current, I did not pursue this curious experiment further. It is probable, that the difference between my results and those of M. de la Rive may depend upon the relative values of the currents used; for I employed only a weak one resulting from two pairs of plates two inches long and half an inch wide, whilst M. de la Rive used four pairs of plates of sixteen square inches in surface.

* * * * *

1641. Electric discharges in the atmosphere in the form of balls of fire have occasionally been described. Such phenomena appear to me to be incompatible with all that we know of electricity and its modes of discharge. As time is an element in the effect (1418. 1436.) it is possible perhaps that an electric discharge might really pass as a ball from place to place; but as every thing shows that its velocity must be almost infinite, and the time of its duration exceedingly small, it is impossible that the eye should perceive it as anything else than a line of light. That phenomena of balls of fire may appear in the atmosphere, I do not mean to deny; but that they have anything to do with the discharge of ordinary electricity, or are at all related to lightning or atmospheric electricity, is much more than doubtful.

* * * * *

1642. All these considerations, and many others, help to confirm the conclusion, drawn over and over again, that the current is an indivisible thing; an axis of power, in every part of which both electric forces are present in equal amount[A] (517. 1627.). With conduction and electrolyzation, and even discharge by spark, such a view will harmonize without hurting any of our preconceived notions; but as relates to convection, a more startling result appears, which must therefore be considered.

[A] I am glad to refer here to the results obtained by Mr. Christie with magneto-electricity, Philosophical Transactions, 1833, p. 113 note. As regards the current in a wire, they confirm everything that I am contending for.

1643. If two balls A and B be electrified in opposite states and held within each other's influence, the moment they move towards each other, a current, or those effects which are understood by the word current, will be produced. Whether A move towards B, or B move in the opposite direction towards A, a current, and in both cases having the same direction, will result. If A and B move from each other, then a current in the opposite direction, or equivalent effects, will be produced.

1644. Or, as charge exists only by induction (1178. 1299.), and a body when electrified is necessarily in relation to other bodies in the opposite state; so, if a ball be electrified positively in the middle of a room and be then moved in any direction, effects will be produced, as current in the same direction (to use the conventional mode of expression) had existed: or, if the ball be negatively electrified, and then moved, effects as if a current in a direction contrary to that of the motion had been formed, will be produced.

1645. I am saying of a single particle or of two what I have before said, in effect, of many (1633.). If the former account of currents be true, then that just stated must be a necessary result. And, though the statement may seem startling at first, it is to be considered that, according to my theory of induction, the charged conductor or particle is related to the distant conductor in the opposite state, or that which terminates the extent of the induction, by all the intermediate particles (1165, 1295.), these becoming polarized exactly as the particles of a solid electrolyte do when interposed between the two electrodes. Hence the conclusion regarding the unity and identity of the current in the case of convection, jointly with the former cases, is not so strange as it might at first appear.

* * * * *

1646. There is a very remarkable phenomenon or effect of the electrolytic discharge, first pointed out, I believe, by Mr. Porrett, of the accumulation of fluid under decomposing action in the current on one side of an interposed diaphragm[A]. It is a mechanical result; and as the liquid passes from the positive towards the negative electrode in all the known cases, it seems to establish a relation to the polar condition of the dielectric in which the current exists (1164. 1525.). It has not as yet been sufficiently investigated by experiment; for De la Rive says[B], it requires that the water should be a bad conductor, as, for instance, distilled water, the effect not happening with strong solutions; whereas, Dutrochet says[C] the contrary is the case, and that, the effect is not directly due to the electric current.

[A] Annals of Philosophy, 1816. viii. p. 75.

[B] Annales de Chimie, 1835. xxviii. p. 196.

[C] Annales de Chimie, 1832, xlix. p. 423.

1647. Becquerel, in his Traite de l'Electricite, has brought together the considerations which arise for and against the opinion, that the effect generally is an electric effect[A]. Though I have no decisive fact to quote at present, I cannot refrain from venturing an opinion, that the effect is analogous both to combination and convection (1623.), being a case of carrying due to the relation of the diaphragm and the fluid in contact with it, through which the electric discharge is jointly effected; and further, that the peculiar relation of positive and negative small and large surfaces already referred to (1482. 1503. 1525.), may be the direct cause of the fluid and the diaphragm travelling in contrary but determinate directions. A very valuable experiment has been made by M. Becquerel with particles of clay[B], which will probably bear importantly on this point.

[A] Vol. iv. p. 192, 197.

[B] Traite de l'Electricite, i. p. 285.

* * * * *

1648. As long as the terms current and electro-dynamic are used to express those relations of the electric forces in which progression of either fluids or effects are supposed to occur (283.), so long will the idea of velocity be associated with them; and this will, perhaps, be more especially the case if the hypothesis of a fluid or fluids be adopted.

1649. Hence has arisen the desire of estimating this velocity either directly or by some effect dependent on it; and amongst the endeavours to do this correctly, may be mentioned especially those of Dr. Watson[A] in 1748, and of Professor Wheatstone[B] in 1834; the electricity in the early trials being supposed to travel from end to end of the arrangement, but in the later investigations a distinction occasionally appearing to be made between the transmission of the effect and of the supposed fluid by the motion of whose particles that effect is produced.

[A] Philosophical Transactions, 1748.

[B] Ibid. 1834, p. 583.

1650. Electrolytic action has a remarkable bearing upon this question of the velocity of the current, especially as connected with the theory of an electric fluid or fluids. In it there is an evident transfer of power with the transfer of each particle of the anion or cathion present, to the next particles of the cathion or anion; and as the amount of power is definite, we have in this way a means of localizing as it were the force, identifying it by the particle and dealing it out in successive portions, which leads, I think, to very striking results.

1651. Suppose, for instance, that water is undergoing decomposition by the powers of a voltaic battery. Each particle of hydrogen as it moves one way, or of oxygen as it moves in the other direction, will transfer a certain amount of electrical force associated with it in the form of chemical affinity (822. 852. 918.) onwards through a distance, which is equal to that through which the particle itself has moved. This transfer will be accompanied by a corresponding movement in the electrical forces throughout every part of the circuit formed (1627. 1634.), and its effects may be estimated, as, for instance, by the heating of a wire (853.) at any particular section of the current however distant. If the water be a cube of an inch in the side, the electrodes touching, each by a surface of one square inch, and being an inch apart, then, by the time that a tenth of it, or 25.25 grs., is decomposed, the particles of oxygen and hydrogen throughout the mass may be considered as having moved relatively to each other in opposite directions, to the amount of the tenth of an inch; i.e. that two particles at first in combination will after the motion be the tenth of an inch apart. Other motions which occur in the fluid will not at all interfere with this result; for they have no power of accelerating or retarding the electric discharge, and possess in fact no relation to it.

1652. The quantity of electricity in 25.25 grains of water is, according to an estimate of the force which I formerly made (861.), equal to above 24 millions of charges of a large Leyden battery; or it would have kept any length of a platina wire 1/104 of an inch in diameter red-hot for an hour and a half (853.). This result, though given only as an approximation, I have seen no reason as yet to alter, and it is confirmed generally by the experiments and results of M. Pouillet[A]. According to Mr. Wheatstone's experiments, the influence or effects of the current would appear at a distance of 576,000 miles in a second[B]. We have, therefore, in this view of the matter, on the one hand, an enormous quantity of power equal to a most destructive thunder-storm appearing instantly at the distance of 576,000 miles from its source, and on the other, a quiet effect, in producing which the power had taken an hour and a half to travel through the tenth of an inch: yet these are the equivalents to each other, being effects observed at the sections of one and the same current (1634.).

[A] Becquerel, Traite de l'Electricite, v. p. 278.

[B] Philosophical Transactions, 1834, p. 589.

* * * * *

1653. It is time that I should call attention to the lateral or transverse forces of the current. The great things which have been achieved by Oersted, Arago, Ampere, Davy, De la Rive, and others, and the high degree of simplification which has been introduced into their arrangement by the theory of Ampere, have not only done their full service in advancing most rapidly this branch of knowledge, but have secured to it such attention that there is no necessity for urging on its pursuit. I refer of course to magnetic action and its relations; but though this is the only recognised lateral action of the current, there is great reason for believing that others exist and would by their discovery reward a close search for them (951.).

1654. The magnetic or transverse action of the current seems to be in a most extraordinary degree independent of those variations or modes of action which it presents directly in its course; it consequently is of the more value to us, as it gives us a higher relation of the power than any that might have varied with each mode of discharge. This discharge, whether it be by conduction through a wire with infinite velocity (1652.), or by electrolyzation with its corresponding and exceeding slow motion (1651.), or by spark, and probably even by convection, produces a transverse magnetic action always the same in kind and direction.

1655. It has been shown by several experimenters, that whilst the discharge is of the same kind the amount of lateral or magnetic force is very constant (216. 366. 367. 368. 376.). But when we wish to compare discharge of different kinds, for the important purpose of ascertaining whether the same amount of current will in its different forms produce the same amount of transverse action, we find the data very imperfect. Davy noticed, that when the electric current was passing through an aqueous solution it affected a magnetic needle[A], and Dr. Ritchie says, that the current in the electrolyte is as magnetic as that in a metallic wire[B], and has caused water to revolve round a magnet as a wire carrying the current would revolve.

[A] Philosophical Transactions, 1821, p. 426.

[B] Ibid. 1832, p. 294.

1656. Disruptive discharge produces its magnetic effects: a strong spark, passed transversely to a steel needle, will magnetise it as well as if the electricity of the spark were conducted by a metallic wire occupying the line of discharge; and Sir H. Davy has shown that the discharge of a voltaic battery in vacuo is affected and has motion given to it by approximated magnets[A].

[A] Philosophical Transactions, 1821, p. 427.

1657. Thus the three very different modes of discharge, namely, conduction, electrolyzation, and disruptive discharge, agree in producing the important transverse phenomenon of magnetism. Whether convection or carrying discharge will produce the same phenomenon has not been determined, and the few experiments I have as yet had time to make do not enable me to answer in the affirmative.

* * * * *

1658. Having arrived at this point in the consideration of the current and in the endeavour to apply its phenomena as tests of the truth or fallacy of the theory of induction which I have ventured to set forth, I am now very much tempted to indulge in a few speculations respecting its lateral action and its possible connexion with the transverse condition of the lines of ordinary induction (1165, 1304.)[A]. I have long sought and still seek for an effect or condition which shall be to statical electricity what magnetic force is to current electricity (1411.); for as the lines of discharge are associated with a certain transverse effect, so it appeared to me impossible but that the lines of tension or of inductive action, which of necessity precede that discharge, should also have their correspondent transverse condition or effect (951.).

[A] Refer for further investigations to 1709.--1736.--Dec. 1838.

1659. According to the beautiful theory of Ampere, the transverse force of a current may be represented by its attraction for a similar current and its repulsion of a contrary current. May not then the equivalent transverse force of static electricity be represented by that lateral tension or repulsion which the lines of inductive action appear to possess (1304.)? Then again, when current or discharge occurs between two bodies, previously under inductrical relations to each other, the lines of inductive force will weaken and fade away, and, as their lateral repulsive tension diminishes, will contract and ultimately disappear in the line of discharge. May not this be an effect identical with the attractions of similar currents? i.e. may not the passage of static electricity into current electricity, and that of the lateral tension of the lines of inductive force into the lateral attraction of lines of similar discharge, have the same relation and dependences, and run parallel to each other?

1660. The phenomena of induction amongst currents which I had the good fortune to discover some years ago (6. &c. 1048.) may perchance here form a connecting link in the series of effects. When a current is first formed, it tends to produce a current in the contrary direction in all the matter around it; and if that matter have conducting properties and be fitly circumstanced, such a current is produced. On the contrary, when the original current is stopped, one in the same direction tends to form all around it, and, in conducting matter properly arranged, will be excited.

1661. Now though we perceive the effects only in that portion of matter which, being in the neighbourhood, has conducting properties, yet hypothetically it is probable, that the nonconducting matter has also its relations to, and is affected by, the disturbing cause, though we have not yet discovered them. Again and again the relation of conductors and non-conductors has been shown to be one not of opposition in kind, but only of degree (1334, 1603.); and, therefore, for this, as well as for other reasons, it is probable, that what will affect a conductor will affect an insulator also; producing perhaps what may deserve the term of the electrotonic state (60. 242. 1114.).

1662. It is the feeling of the necessity of some lateral connexion between the lines of electric force (1114.); of some link in the chain of effects as yet unrecognised, that urges me to the expression of these speculations. The same feeling has led me to make many experiments on the introduction of insulating dielectrics having different inductive capacities (1270. 1277.) between magnetic poles and wires carrying currents, so as to pass across the lines of magnetic force. I have employed such bodies both at rest and in motion, without, as yet, being able to detect any influence produced by them; but I do by no means consider the experiments as sufficiently delicate, and intend, very shortly, to render them more decisive[A].

[A] See onwards 1711.--1726.--Dec. 1838.

1663. I think the hypothetical question may at present be put thus: can such considerations as those already generally expressed (1658.) account for the transverse effects of electrical currents? are two such currents in relation to each other merely by the inductive condition of the particles of matter between them, or are they in relation by some higher quality and condition (1654.), which, acting at a distance and not by the intermediate particles, has, like the force of gravity, no relation to them?

1664. If the latter be the case, then, when electricity is acting upon and in matter, its direct and its transverse action are essentially different in their nature; for the former, if I am correct, will depend upon the contiguous particles, and the latter will not. As I have said before, this may be so, and I incline to that view at present; but I am desirous of suggesting considerations why it may not, that the question may be thoroughly sifted.

1665. The transverse power has a character of polarity impressed upon it. In the simplest forms it appears as attraction or repulsion, according as the currents are in the same or different directions: in the current and the magnet it takes up the condition of tangential forces; and in magnets and their particles produces poles. Since the experiments have been made which have persuaded me that the polar forces of electricity, as in induction and electrolytic action (1298. 1343.), show effects at a distance only by means of the polarized contiguous and intervening particles, I have been led to expect that all polar forces act in the same general manner; and the other kinds of phenomena which one can bring to bear upon the subject seem fitted to strengthen that expectation. Thus in crystallizations the effect is transmitted from particle to particle; and in this manner, in acetic acid or freezing water a crystal a few inches or even a couple of feet in length will form in less than a second, but progressively and by a transmission of power from particle to particle. And, as far as I remember, no case of polar action, or partaking of polar action, except the one under discussion, can be found which does not act by contiguous particles[A]. It is apparently of the nature of polar forces that such should be the case, for the one force either finds or developed the contrary force near to it, and has, therefore, no occasion to seek for it at a distance.

[A] I mean by contiguous particles those which are next to each other, not that there is no space between them. See (1616.).

1666. But leaving these hypothetical notions respecting the nature of the lateral action out of sight, and returning to the direct effects, I think that the phenomena examined and reasoning employed in this and the two preceding papers tend to confirm the view first taken (1464.), namely, that ordinary inductive action and the effects dependent upon it are due to an action of the contiguous particles of the dielectric interposed between the charged surfaces or parts which constitute, as it were, the terminations of the effect. The great point of distinction and power (if it have any) in the theory is, the making the dielectric of essential and specific importance, instead of leaving it as it were a mere accidental circumstance or the simple representative of space, having no more influence over the phenomena than the space occupied by it. I have still certain other results and views respecting the nature of the electrical forces and excitation, which are connected with the present theory; and, unless upon further consideration they sink in my estimation, I shall very shortly put them into form as another series of these electrical researches.

_Royal Institution. February 14th, 1838._

FOURTEENTH SERIES.

S 20. Nature of the electric force or forces. S 21. Relation of the electric and magnetic forces. S 22. Note on electrical excitation.

Received June 21, 1838.--Read June 21, 1838.

S 20. Nature of the electric force or forces.

1667. The theory of induction set forth and illustrated in the three preceding series of experimental researches does not assume anything new as to the nature of the electric force or forces, but only as to their distribution. The effects may depend upon the association of one electric fluid with the particles of matter, as in the theory of Franklin, Epinus, Cavendish, and Mossotti; or they may depend upon the association of two electric fluids, as in the theory of Dufay and Poisson; or they may not depend upon anything which can properly be called the electric fluid, but on vibrations or other affections of the matter in which they appear. The theory is unaffected by such differences in the mode of viewing the nature of the forces; and though it professes to perform the important office of stating how the powers are arranged (at least in inductive phenomena), it does not, as far as I can yet perceive, supply a single experiment which can be considered as a distinguishing test of the truth of any one of these various views,

1668. But, to ascertain how the forces are arranged, to trace them in their various relations to the particles of matter, to determine their general laws, and also the specific differences which occur under these laws, is as important as, if not more so than, to know whether the forces reside in a fluid or not; and with the hope of assisting in this research, I shall offer some further developments, theoretical and experimental, of the conditions under which I suppose the particles of matter are placed when exhibiting inductive phenomena.

1669. The theory assumes that all the particles, whether of insulating or conducting matter, are as wholes conductors.

1670. That not being polar in their normal state, they can become so by the influence of neighbouring charged particles, the polar state being developed at the instant, exactly as in an insulated conducting mass consisting of many particles.

1671. That the particles when polarized are in a forced state, and tend to return to their normal or natural condition.

1672. That being as wholes conductors, they can readily be charged, either bodily or polarly.

1673. That particles which being contiguous[A] are also in the line of inductive action can communicate or transfer their polar forces one to another more or less readily.

[A] See note to 1164.--Dec. 1838.

1674. That those doing so less readily require the polar forces to be raised to a higher degree before this transference or communication takes place.

1675. That the ready communication of forces between contiguous particles constitutes conduction, and the difficult communication insulation; conductors and insulators being bodies whose particles naturally possess the property of communicating their respective forces easily or with difficulty; having these differences just as they have differences of any other natural property.

1676. That ordinary induction is the effect resulting from the action of matter charged with excited or free electricity upon insulating matter, tending to produce in it an equal amount of the contrary state.

1677. That it can do this only by polarizing the particles contiguous to it, which perform the same office to the next, and these again to those beyond; and that thus the action is propagated from the excited body to the next conducting mass, and there renders the contrary force evident in consequence of the effect of communication which supervenes in the conducting mass upon the polarization of the particles of that body (1675.).

1678. That therefore induction can only take place through or across insulators; that induction is insulation, it being the necessary consequence of the state of the particles and the mode in which the influence of electrical forces is transferred or transmitted through or across such insulating media.

1679. The particles of an insulating dielectric whilst under induction may be compared to a series of small magnetic needles, or more correctly still to a series of small insulated conductors. If the space round a charged globe were filled with a mixture of an insulating dielectric, as oil of turpentine or air, and small globular conductors, as shot, the latter being at a little distance from each other so as to be insulated, then these would in their condition and action exactly resemble what I consider to be the condition and action of the particles of the insulating dielectric itself (1337.). If the globe were charged, these little conductors would all be polar; if the globe were discharged, they would all return to their normal state, to be polarized again upon the recharging of the globe. The state developed by induction through such particles on a mass of conducting mutter at a distance would be of the contrary kind, and exactly equal in amount to the force in the inductric globe. There would be a lateral diffusion of force (1224. 1297.), because each polarized sphere would be in an active or tense relation to all those contiguous to it, just as one magnet can affect two or more magnetic needles near it, and these again a still greater number beyond them. Hence would result the production of curved lines of inductive force if the inducteous body in such a mixed dielectric were an uninsulated metallic ball (1219. &c.) or other properly shaped mass. Such curved lines are the consequences of the two electric forces arranged as I have assumed them to be: and, that the inductive force can be directed in such curved lines is the strongest proof of the presence of the two powers and the polar condition of the dielectric particles.

1680. I think it is evident, that in the case stated, action at a distance can only result through an action of the contiguous conducting particles. There is no reason why the inductive body should polarize or affect distant conductors and leave those near it, namely the particles of the dielectric, unaffected: and everything in the form of fact and experiment with conducting masses or particles of a sensible size contradicts such a supposition.

1681. A striking character of the electric power is that it is limited and exclusive, and that the two forces being always present are exactly equal in amount. The forces are related in one of two ways, either as in the natural normal condition of an uncharged insulated conductor; or as in the charged state, the latter being a case of induction.

1682. Cases of induction are easily arranged so that the two forces being limited in their direction shall present no phenomena or indications external to the apparatus employed, Thus, if a Leyden jar, having its external coating a little higher than the internal, be charged and then its charging ball and rod removed, such jar will present no electrical appearances so long as its outside is uninsulated. The two forces which may be said to be in the coatings, or in the particles of the dielectric contiguous to them, are entirely engaged to each other by induction through the glass; and a carrier ball (1181.) applied either to the inside or outside of the jar will show no signs of electricity. But if the jar be insulated, and the charging ball and rod, in an uncharged state and suspended by an insulating thread of white silk, be restored to their place, then the part projecting above the jar will give electrical indications and charge the carrier, and at the same time the outside coating of the jar will be found in the opposite state and inductric towards external surrounding objects.

1683. These are simple consequences of the theory. Whilst the charge of the inner coating could induce only through the glass towards the outer coating, and the latter contained no more of the contrary force than was equivalent to it, no induction external to the jar could be perceived; but when the inner coating was extended by the rod and ball so that it could induce through the air towards external objects, then the tension of the polarized glass molecules would, by their tendency to return to the normal state, fall a little, and a portion of the charge passing to the surface of this new part of the inner conductor, would produce inductive action through the air towards distant objects, whilst at the same time a part of the force in the outer coating previously directed inwards would now be at liberty, and indeed be constrained to induct outwards through the air, producing in that outer coating what is sometimes called, though I think very improperly, free charge. If a small Leyden jar be converted into that form of apparatus usually known by the name of the electric well, it will illustrate this action very completely.

1684. The terms free charge and dissimulated electricity convey therefore erroneous notions if they are meant to imply any difference as to the mode or kind of action. The charge upon an insulated conductor in the middle of a room is in the same relation to the walls of that room as the charge upon the inner coating of a Leyden jar is to the outer coating of the same jar. The one is not more free or more dissimulated than the other; and when sometimes we make electricity appear where it was not evident before, as upon the outside of a charged jar, when, after insulating it, we touch the inner coating, it is only because we divert more or less of the inductive force from one direction into another; for not the slightest change is in such circumstances impressed upon the character or action of the force.

* * * * *

1685. Having given this general theoretical view, I will now notice particular points relating to the nature of the assumed electric polarity of the insulating dielectric particles.

1686. The polar state may be considered in common induction as a forced state, the particles tending to return to their normal condition. It may probably be raised to a very high degree by approximation of the inductric and inducteous bodies or by other circumstances; and the phenomena of electrolyzation (861. 1652. 1796.) seem to imply that the quantity of power which can thus be accumulated on a single particle is enormous. Hereafter we may be able to compare corpuscular forces, as those of gravity, cohesion, electricity, and chemical affinity, and in some way or other from their effects deduce their relative equivalents; at present we are not able to do so, but there seems no reason to doubt that their electrical, which are at the same time their chemical forces (891. 918.), will be by far the most energetic.

1687. I do not consider the powers when developed by the polarization as limited to two distinct points or spots on the surface of each particle to be considered as the poles of an axis, but as resident on large portions of that surface, as they are upon the surface of a conductor of sensible size when it is thrown into a polar state. But it is very probable, notwithstanding, that the particles of different bodies may present specific differences in this respect, the powers not being equally diffused though equal in quantity; other circumstances also, as form and quality, giving to each a peculiar polar relation. It is perhaps to the existence of some such differences as these that we may attribute the specific actions of the different dielectrics in relation to discharge(1394. 1508.). Thus with respect to oxygen and nitrogen singular contrasts were presented when spark and brush discharge were made to take place in these gases, as may be seen by reference to the Table in paragraph 1518 of the Thirteenth Series; for with nitrogen, when the small, negative or the large positive ball was rendered inductric, the effects corresponded with those which in oxygen were produced when the small positive or the large negative ball was rendered inductric.

1688. In such solid bodies as glass, lac, sulphur, &c., the particles appear to be able to become polarized in all directions, for a mass when experimented upon so as to ascertain its inductive capacity in three or more directions (1690.), gives no indication of a difference. Now as the particles are fixed in the mass, and as the direction of the induction through them must change with its change relative to the mass, the constant effect indicates that they can be polarized electrically in any direction. This accords with the view already taken of each particle as a whole being a conductor (1669.), and, as an experimental fact, helps to confirm that view.

1689. But though particles may thus be polarized in any direction under the influence of powers which are probably of extreme energy (1686.), it does not follow that each particle may not tend to polarize to a greater degree, or with more facility, in one direction than another; or that different kinds may not have specific differences in this respect, as they have differences of conducting and other powers (1296. 1326. 1395.). I sought with great anxiety for a relation of this nature; and selecting crystalline bodies as those in which all the particles are symmetrically placed, and therefore best fitted to indicate any result which might depend upon variation of the direction of the forces to the direction of the particles in which they were developed, experimented very carefully with them. I was the more strongly stimulated to this inquiry by the beautiful electrical condition of the crystalline bodies tourmaline and boracite, and hoped also to discover a relation between electric polarity and that of crystallization, or even of cohesion itself (1316.). My experiments have not established any connexion of the kind sought for. But as I think it of equal importance to show either that there is or is not such a relation, I shall briefly describe the results.

1690. The form of experiment was as follows. A brass ball 0.73 of an inch in diameter, fixed at the end of a horizontal brass rod, and that at the end of a brass cylinder, was by means of the latter connected with a large Leyden battery (291.) by perfect metallic communications, the object being to keep that ball, by its connexion with the charged battery in an electrified state, very nearly uniform, for half an hour at a time. This was the inductric ball. The inducteous ball was the carrier of the torsion electrometer (1229. 1314.); and the dielectric between them was a cube cut from a crystal, so that two of its faces should be perpendicular to the optical axis, whilst the other four were parallel to it. A small projecting piece of shell-lac was fixed on the inductric ball at that part opposite to the attachment of the brass rod, for the purpose of preventing actual contact between the ball and the crystal cube. A coat of shell-lac was also attached to that side of the carrier ball which was to be towards the cube, being also that side which was furthest from the repelled ball in the electrometer when placed in its position in that instrument. The cube was covered with a thin coat of shell-lac dissolved in alcohol, to prevent the deposition of damp upon its surface from the air. It was supported upon a small table of shell-lac fixed on the top of a stem of the same substance, the latter being of sufficient strength to sustain the cube, and yet flexible enough from its length to act as a spring, and allow the cube to bear, when in its place, against the shell-lac on the inductric ball.

1691. Thus it was easy to bring the inducteous ball always to the same distance from the inductric bull, and to uninsulate and insulate it again in its place; and then, after measuring the force in the electrometer (1181.), to return it to its place opposite to the inductric ball for a second observation. Or it was easy by revolving the stand which supported the cube to bring four of its faces in succession towards the inductric ball, and so observe the force when the lines of inductive action (1304.) coincided with, or were transverse to, the direction of the optical axis of the crystal. Generally from twenty to twenty-eight observations were made in succession upon the four vertical faces of a cube, and then an average expression of the inductive force was obtained, and compared with similar averages obtained at other times, every precaution being taken to secure accurate results.

1692. The first cube used was of rock crystal; it was 0.7 of an inch in the side. It presented a remarkable and constant difference, the average of not less than 197 observations, giving 100 for the specific inductive capacity in the direction coinciding with the optical axis of the cube, whilst 93.59 and 93.31 were the expressions for the two transverse directions.

1693. But with a second cube of rock crystal corresponding results were not obtained. It was 0.77 of an inch in the side. The average of many experiments gave 100 for the specific inductive capacity coinciding with the direction of the optical axis, and 98.6 and 99.92 for the two other directions.

1694. Lord Ashley, whom I have found ever ready to advance the cause of science, obtained for me the loan of three globes of rock crystal belonging to Her Grace the Duchess of Sutherland for the purposes of this investigation. Two had such fissures as to render them unfit for the experiments (1193. 1698.). The third, which was very superior, gave me no indications of any difference in the inductive force for different directions.

1695. I then used cubes of Iceland spar. One 0.5 of an inch in diameter gave 100 for the axial direction, and 98.66 and 95.74 for the two cross directions. The other, 0.8 of an inch in the side, gave 100 for the axial direction, whilst 101.73 and 101.86 were the numbers for the cross direction.

1696. Besides these differences there were others, which I do not think it needful to state, since the main point is not confirmed. For though the experiments with the first cube raised great expectation, they have not been generalized by those which followed. I have no doubt of the results as to that cube, but they cannot as yet be referred to crystallization. There are in the cube some faintly coloured layers parallel to the optical axis, and the matter which colours them may have an influence; but then the layers are also nearly parallel to a cross direction, and if at all influential should show some effect in that direction also, which they did not.

1697. In some of the experiments one half or one part of a cube showed a superiority to another part, and this I could not trace to any charge the different parts had received. It was found that the varnishing of the cubes prevented any communication of charge to them, except (in a few experiments) a small degree of the negative state, or that which was contrary to the state of the inductric ball (1564. 1566.).

1698. I think it right to say that, as far as I could perceive, the insulating character of the cubes used was perfect, or at least so nearly perfect, as to bear a comparison with shell-lac, glass, &c. (1255). As to the cause of the differences, other than regular crystalline structure, there may be several. Thus minute fissures in the crystal insensible to the eye may be so disposed as to produce a sensible electrical difference (1193.). Or the crystallization may be irregular; or the substance may not be quite pure; and if we consider how minute a quantity of matter will alter greatly the conducting power of water, it will seem not unlikely that a little extraneous matter diffused through the whole or part of a cube, may produce effects sufficient to account for all the irregularities of action that have been observed.

1699. An important inquiry regarding the electrical polarity of the particles of an insulating dielectric, is, whether it be the molecules of the particular substance acted on, or the component or ultimate particles, which thus act the part of insulated conducting polarizing portions (1669.).

1700. The conclusion I have arrived at is, that it is the molecules of the substance which polarize as wholes (1347.); and that however complicated the composition of a body may be, all those particles or atoms which are held together by chemical affinity to form one molecule of the resulting body act as one conducting mass or particle when inductive phenomena and polarization are produced in the substance of which it is a part.

1701. This conclusion is founded on several considerations. Thus if we observe the insulating and conducting power of elements when they are used as dielectrics, we find some, as sulphur, phosphorus, chlorine, iodine, &c., whose particles insulate, and therefore polarize in a high degree; whereas others, as the metals, give scarcely any indication of possessing a sensible proportion of this power (1328.), their particles freely conducting one to another. Yet when these enter into combination they form substances having no direct relation apparently, in this respect, to their elements; for water, sulphuric acid, and such compounds formed of insulating elements, conduct by comparison freely; whilst oxide of lead, flint glass, borate of lead, and other metallic compounds containing very high proportions of conducting matter, insulate excellently well. Taking oxide of lead therefore as the illustration, I conceive that it is not the particles of oxygen and lead which polarize separately under the act of induction, but the molecules of oxide of lead which exhibit this effect, all the elements of one particle of the resulting body, being held together as parts of one conducting individual by the bonds of chemical affinity; which is but another term for electrical force (918.).

1702. In bodies which are electrolytes we have still further reason for believing in such a state of things. Thus when water, chloride of tin, iodide of lead, &c. in the solid state are between the electrodes of the voltaic battery, their particles polarize as those of any other insulating dielectric do (1164.); but when the liquid state is conferred on these substances, the polarized particles divide, the two halves, each in a highly charged state, travelling onwards until they meet other particles in an opposite and equally charged state, with which they combine, to the neutralization of their chemical, i.e. their electrical forces, and the reproduction of compound particles, which can again polarize as wholes, and again divide to repeat the same series of actions (1347.).

1703. But though electrolytic particles polarize as wholes, it would appear very evident that in them it is not a matter of entire indifference how the particle polarizes (1689.), since, when free to move (380, &c.) the polarities are ultimately distributed in reference to the elements; and sums of force equivalent to the polarities, and very definite in kind and amount, separate, as it were, from each other, and travel onwards with the elementary particles. And though I do not pretend to know what an atom is, or how it is associated or endowed with electrical force, or how this force is arranged in the cases of combination and decomposition, yet the strong belief I have in the electrical polarity of particles when under inductive action, and the hearing of such an opinion on the general effects of induction, whether ordinary or electrolytic, will be my excuse, I trust, for a few hypothetical considerations.

1704 In electrolyzation it appears that the polarized particles would (because of the gradual change which has been induced upon the chemical, i.e. the electrical forces of their elements (918.)) rather divide than discharge to each other without division (1348.); for if their division, i.e. their decomposition and recombination, be prevented by giving them the solid state, then they will insulate electricity perhaps a hundredfold more intense than that necessary for their electrolyzation (419, &c.). Hence the tension necessary for direct conduction in such bodies appears to be much higher than that for decomposition (419. 1164. 1344.).

1705. The remarkable stoppage of electrolytic conduction by solidification (380. 1358.), is quite consistent with these views of the dependence of that process on the polarity which is common to all insulating matter when under induction, though attended by such peculiar electro-chemical results in the case of electrolytes. Thus it may be expected that the first effect of induction is so to polarize and arrange the particles of water that the positive or hydrogen pole of each shall be from the positive electrode and towards the negative electrode, whilst the negative or oxygen pole of each shall be in the contrary direction; and thus when the oxygen and hydrogen of a particle of water have separated, passing to and combining with other hydrogen and oxygen particles, unless these new particles of water could turn round they could not take up that position necessary for their successful electrolytic polarization. Now solidification, by fixing the water particles and preventing them from assuming that essential preliminary position, prevents also their electrolysis (413.); and so the transfer of forces in that manner being prevented (1347. 1703.), the substance acts as an ordinary insulating dielectric (for it is evident by former experiments (419. 1704.) that the insulating tension is higher than the electrolytic tension), induction through it rises to a higher degree, and the polar condition of the molecules as wholes, though greatly exalted, is still securely maintained.

1706. When decomposition happens in a fluid electrolyte, I do not suppose that all the molecules in the same sectional plane (1634.) part with and transfer their electrified particles or elements at once. Probably the discharge force for that plane is summed up on one or a few particles, which decomposing, travelling and recombining, restore the balance of forces, much as in the case of spark disruptive discharge (1406.); for as those molecules resulting from particles which have just transferred power must by their position (1705.) be less favourably circumstanced than others, so there must be some which are most favourably disposed, and these, by giving way first, will for the time lower the tension and produce discharge.

1707. In former investigations of the action of electricity (821, &c.) it was shown, from many satisfactory cases, that the quantity of electric power transferred onwards was in proportion to and was definite for a given quantity of matter moving as anion or cathion onwards in the electrolytic line of action; and there was strong reason to believe that each of the particles of matter then dealt with, had associated with it a definite amount of electrical force, constituting its force of chemical affinity, the chemical equivalents and the electro-chemical equivalents being the same (836.). It was also found with few, and I may now perhaps say with no exceptions (1341.), that only those compounds containing elements in single proportions could exhibit the characters and phenomena of electrolytes (697.); oxides, chlorides, and other bodies containing more than one proportion of the electro-negative element refusing to decompose under the influence of the electric current.

1708. Probable reasons for these conditions and limitations arise out of the molecular theory of induction. Thus when a liquid dielectric, as chloride of tin, consists of molecules, each composed of a single particle of each of the elements, then as these can convey equivalent opposite forces by their separation in opposite directions, both decomposition and transfer can result. But when the molecules, as in the bichloride of tin, consist of one particle or atom of one element, and two of the other, then the simplicity with which the particles may be supposed to be arranged and to act, is destroyed. And, though it may be conceived that when the molecules of bichloride of tin are polarized as wholes by the induction across them, the positive polar force might accumulate on the one particle of tin whilst the negative polar force accumulated on the two particles of chlorine associated with it, and that these might respectively travel right and left to unite with other two of chlorine and one of tin, in analogy with what happens in cases of compounds consisting of single proportions, yet this is not altogether so evident or probable. For when a particle of tin combines with two of chlorine, it is difficult to conceive that there should not be some relation of the three in the resulting molecule analogous to fixed position, the one particle of metal being perhaps symmetrically placed in relation to the two of chlorine: and, it is not difficult to conceive of such particles that they could not assume that position dependent both on their polarity and the relation of their elements, which appears to be the first step in the process of electrolyzation (1345. 1705.).

S 21. Relation of the electric and magnetic forces.

1709. I have already ventured a few speculations respecting the probable relation of magnetism, as the transverse force of the current, to the divergent or transverse force of the lines of inductive action belonging to static electricity (1658, &c.).

1710. In the further consideration of this subject it appeared to me to be of the utmost importance to ascertain, if possible, whether this lateral action which we call magnetism, or sometimes the induction of electrical currents (26. 1048, &c.), is extended to a distance by the action of the intermediate particles in analogy with the induction of static electricity, or the various effects, such as conduction, discharge, &c., which are dependent on that induction; or, whether its influence at a distance is altogether independent of such intermediate particles (1662.).

1711. I arranged two magneto-electric helices with iron cores end to end, but with an interval of an inch and three quarters between them, in which interval was placed the end or pole of a bar magnet. It is evident, that on moving the magnetic pole from one core towards the other, a current would tend to form in both helices, in the one because of the lowering, and in the other because of the strengthening of the magnetism induced in the respective soft iron cores. The helices were connected together, and also with a galvanometer, so that these two currents should coincide in direction, and tend by their joint force to deflect the needle of the instrument. The whole arrangement was so effective and delicate, that moving the magnetic pole about the eighth of an inch to and fro two or three times, in periods equal to those required for the vibrations of the galvanometer needle, was sufficient to cause considerable vibration in the latter; thus showing readily the consequence of strengthening the influence of the magnet on the one core and helix, and diminishing it on the other.

1712. Then without disturbing the distances of the magnet and cores, plates of substances were interposed. Thus calling the two cores A and B, a plate of shell-lac was introduced between the magnetic pole and A for the time occupied by the needle in swinging one way; then it was withdrawn for the time occupied in the return swing; introduced again for another equal portion of time; withdrawn for another portion, and so on eight or nine times; but not the least effect was observed on the needle. In other cases the plate was alternated, i.e. it was introduced between the magnet and A for one period of time, withdrawn and introduced between the magnet and B for the second period, withdrawn and restored to its first place for the third period, and so on, but with no effect on the needle.

1713. In these experiments shell-lac in plates 0.9 of an inch in thickness, sulphur in a plate 0.9 of an inch in thickness, and copper in a plate 0.7 of an inch in thickness were used without any effect. And I conclude that bodies, contrasted by the extremes of conducting and insulating power, and opposed to each other as strongly as metals, air, and sulphur, show no difference with respect to magnetic forces when placed in their lines of action, at least under the circumstances described.

1714. With a plate of iron, or even a small piece of that metal, as the head of a nail, a very different effect was produced, for then the galvanometer immediately showed its sensibility, and the perfection of the general arrangement.

1715. I arranged matters so that a plate of copper 0.2 of an inch in thickness, and ten inches in diameter, should have the part near the edge interposed between the magnet and the core, in which situation it was first rotated rapidly, and then held quiescent alternately, for periods according with that required for the swinging of the needle; but not the least effect upon the galvanometer was produced.

1716. A plate of shell-lac 0.6 of an inch in thickness was applied in the same manner, but whether rotating or not it produced no effect.

1717. Occasionally the plane of rotation was directly across the magnetic curve: at other times it was made as oblique as possible; the direction of the rotation being also changed in different experiments, but not the least effect was produced.

1718. I now removed the helices with their soft iron cores, and replaced them by two flat helices wound upon card board, each containing forty-two feet of silked copper wire, and having no associated iron. Otherwise the arrangement was as before, and exceedingly sensible; for a very slight motion of the magnet between the helices produced an abundant vibration of the galvanometer needle.

1719. The introduction of plates of shell-lac, sulphur, or copper into the intervals between the magnet and these helices (1713.), produced not the least effect, whether the former were quiescent or in rapid revolution (1715.). So here no evidence of the influence of the intermediate particles could be obtained (1710.).

1720. The magnet was then removed and replaced by a flat helix, corresponding to the two former, the three being parallel to each other. The middle helix was so arranged that a voltaic current could be sent through it at pleasure. The former galvanometer was removed, and one with a double coil employed, one of the lateral helices being connected with one coil, and the other helix with the other coil, in such manner that when a voltaic current was sent through the middle helix its inductive action (26.) on the lateral helices should cause currents in them, having contrary directions in the coils of the galvanometer. By a little adjustment of the distances these induced currents were rendered exactly equal, and the galvanometer needle remained stationary notwithstanding their frequent production in the instrument. I will call the middle coil C, and the external coils A and B.

1721. A plate of copper 0.7 of an inch thick and six inches square, was placed between coils C and B, their respective distances remaining unchanged; and then a voltaic current from twenty pairs of 4 inch plates was sent through the coil C, and intermitted, in periods fitted to produce an effect on the galvanometer (1712.). if any difference had been produced in the effect of C on A and B. But notwithstanding the presence of air in one interval and copper in the other, the inductive effect was exactly alike on the two coils, and as if air had occupied both intervals. So that notwithstanding the facility with which any induced currents might form in the thick copper plate, the coil outside of it was just as much affected by the central helix C as if no such conductor as the copper had been there (65.).

1722. Then, for the copper plate was substituted one of sulphur 0.9 of an inch thick; still the results were exactly the same, i.e. there was no action at the galvanometer.

1723. Thus it appears that when a voltaic current in one wire is exerting its inductive action to produce a contrary or a similar current in a neighbouring wire, according as the primary current is commencing or ceasing, it makes not the least difference whether the intervening space is occupied by such insulating bodies as air, sulphur and shell-lac, or such conducting bodies as copper, and the other non-magnetic metals.

1724. A correspondent effect was obtained with the like forces when resident in a magnet thus. A single flat helix (1718.) was connected with a galvanometer, and a magnetic pole placed near to it; then by moving the magnet to and from the helix, or the helix to and from the magnet, currents were produced indicated by the galvanometer.

1725. The thick copper plate (1721.) was afterwards interposed between the magnetic pole and the helix; nevertheless on moving these to and fro, effects, exactly the same in direction and amount, were obtained as if the copper had not been there. So also on introducing a plate of sulphur into the interval, not the least influence on the currents produced by motion of the magnet or coils could be obtained.

1726. These results, with many others which I have not thought it needful to describe, would lead to the conclusion that (judging by the amount of effect produced at a distance by forces transverse to the electric current, i.e. magnetic forces,) the intervening matter, and therefore the intervening particles, have nothing to do with the phenomena; or in other words, that though the inductive force of static electricity is transmitted to a distance by the action of the intermediate particles (1164. 1666.), the transverse inductive force of currents, which can also act at a distance, is not transmitted by the intermediate particles in a similar way.

1727. It is however very evident that such a conclusion cannot be considered as proved. Thus when the metal copper is between the pole and the helix (1715. 1719. 1725.) or between the two helices (1721.) we know that its particles are affected, and can by proper arrangements make their peculiar state for the time very evident by the production of either electrical or magnetical effects. It seems impossible to consider this effect on the particles of the intervening matter as independent of that produced by the inductric coil or magnet C, on the inducteous coil or core A (1715. 1721.); for since the inducteous body is equally affected by the inductric body whether these intervening and affected particles of copper are present or not (1723. 1725.), such a supposition would imply that the particles so affected had no reaction back on the original inductric forces. The more reasonable conclusion, as it appears to me, is, to consider these affected particles as efficient in continuing the action onwards from the inductric to the inducteous body, and by this very communication producing the effect of no loss of induced power at the latter.

1728. But then it may be asked what is the relation of the particles of insulating bodies, such as air, sulphur, or lac, when they intervene in the line of magnetic action? The answer to this is at present merely conjectural. I have long thought there must be a particular condition of such bodies corresponding to the state which causes currents in metals and other conductors (26. 53. 191. 201. 213.); and considering that the bodies are insulators one would expect that state to be one of tension. I have by rotating non-conducting bodies near magnetic poles and poles near them, and also by causing powerful electric currents to be suddenly formed and to cease around and about insulators in various directions, endeavoured to make some such state sensible, but have not succeeded. Nevertheless, as any such state must be of exceedingly low intensity, because of the feeble intensity of the currents which are used to induce it, it may well be that the state may exist, and may be discoverable by some more expert experimentalist, though I have not been able to make it sensible.

1729. It appears to me possible, therefore, and even probable, that magnetic action may be communicated to a distance by the action of the intervening particles, in a manner having a relation to the way in which the inductive forces of static electricity are transferred to a distance (1677.); the intervening particles assuming for the time more or less of a peculiar condition, which (though with a very imperfect idea) I have several times expressed by the term electro-tonic state (60. 242. 1114. 1661.). I hope it will not be understood that I hold the settled opinion that such is the case. I would rather in fact have proved the contrary, namely, that magnetic forces are quite independent of the matter intervening between the inductric and the inductions bodies; but I cannot get over the difficulty presented by such substances as copper, silver, lead, gold, carbon, and even aqueous solutions (201. 213.), which though they are known to assume a peculiar state whilst intervening between the bodies acting and acted upon (1727.), no more interfere with the final result than those which have as yet had no peculiarity of condition discovered in them.

1730. A remark important to the whole of this investigation ought to be made here. Although I think the galvanometer used as I have described it (1711. 1720.) is quite sufficient to prove that the final amount of action on each of the two coils or the two cores A and B (1713. 1719.) is equal, yet there is an effect which may be consequent on the difference of action of two interposed bodies which it would not show. As time enters as an element into these actions[A] (125.), it is very possible that the induced actions on the helices or cores A, B, though they rise to the same degree when air and copper, or air and lac are contrasted as intervening substances, do not do so in the same time; and yet, because of the length of time occupied by a vibration of the needle, this difference may not be visible, both effects rising to their maximum in periods so short as to make no sensible portion of that required for a vibration of the needle, and so exert no visible influence upon it.

[A] See Annnles de Chimie, 1833, tom. li. pp. 422, 428.

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1731. If the lateral or transverse force of electrical currents, or what appears to be the same thing, magnetic power, could be proved to be influential at a distance independently of the intervening contiguous particles, then, as it appears to me, a real distinction of a high and important kind, would be established between the natures of these two forces (1654. 1664.). I do not mean that the powers are independent of each other and might be rendered separately active, on the contrary they are probably essentially associated (1654.), but it by no means follows that they are of the same nature. In common statical induction, in conduction, and in electrolyzation, the forces at the opposite extremities of the particles which coincide with the lines of action and have commonly been distinguished by the term electric, are polar, and in the cases of contiguous particles act only to insensible distances; whilst those which are transverse to the direction of these lines, and are called magnetic, are circumferential, act at a distance, and if not through the mediation of the intervening particles, have their relations to ordinary matter entirely unlike those of the electrical forces with which they are associated.

1732. To decide this question of the identity or distinction of the two kinds of power, and establish their true relation, would be exceedingly important. The question seems fully within the reach of experiment, and offers a high reward to him who will attempt its settlement.

1733. I have already expressed a hope of finding an effect or condition which shall be to statical electricity what magnetic force is to current electricity (1658.). If I could have proved to my own satisfaction that magnetic forces extended their influence to a distance by the conjoined action of the intervening particles in a manner analogous to that of electrical forces, then I should have thought that the natural tension of the lines of inductive action (1659.), or that state so often hinted at as the electro-tonic state (1661. 1662.), was this related condition of statical electricity.

1734. It may be said that the state of no lateral action is to static or inductive force the equivalent of magnetism to current force; but that can only be upon the view that electric and magnetic action are in their nature essentially different (1664.). If they are the same power, the whole difference in the results being the consequence of the difference of direction, then the normal or undeveloped state of electric force will correspond with the state of no lateral action of the magnetic state of the force; the electric current will correspond with the lateral effects commonly called magnetism; but the state of static induction which is between the normal condition and the current will still require a corresponding lateral condition in the magnetic series, presenting its own peculiar phenomena; for it can hardly be supposed that the normal electric, and the inductive or polarized electric, condition, can both have the same lateral relation. If magnetism be a separate and a higher relation of the powers developed, then perhaps the argument which presses for this third condition of that force would not be so strong.

1735. I cannot conclude these general remarks upon the relation of the electric and magnetic forces without expressing my surprise at the results obtained with the copper plate (1724. 1725.). The experiments with the flat helices represent one of the simplest cases of the induction of electrical currents (1720.); the effect, as is well known, consisting in the production of a momentary current in a wire at the instant when a current in the contrary direction begins to pass through a neighbouring parallel wire, and the production of an equally brief current in the reverse direction when the determining current is stopped (26.). Such being the case, it seems very extraordinary that this induced current which takes place in the helix A when there is only air between A and C (1720.). should be equally strong when that air is replaced by an enormous mass of that excellently conducting metal copper (1721.). It might have been supposed that this mass would have allowed of the formation and discharge of almost any quantity of currents in it, which the helix C was competent to induce, and so in some degree have diminished if not altogether prevented the effect in A: instead of which, though we can hardly doubt that an infinity of currents are formed at the moment in the copper plate, still not the smallest diminution or alteration of the effect in A appears (65.). Almost the only way of reconciling this effect with generally received notions is, as it appears to me, to admit that magnetic action is communicated by the action of the intervening particles (1729. 1733.).

1736. This condition of things, which is very remarkable, accords perfectly with the effects observed in solid helices where wires are coiled over wires to the amount of five or six or more layers in succession, no diminution of effect on the outer ones being occasioned by those within.

S 22. Note on electrical excitation.

1737. That the different modes in which electrical excitement takes place will some day or other be reduced under one common law can hardly be doubted, though for the present we are bound to admit distinctions. It will be a great point gained when these distinctions are, not removed, but understood.

1738. The strict relation of the electrical and chemical powers renders the chemical mode of excitement the most instructive of all, and the case of two isolated combining particles is probably the simplest that we possess. Here however the action is local, and we still want such a test of electricity as shall apply to it, to cases of current electricity, and also to those of static induction. Whenever by virtue of the previously combined condition of some of the acting particles (923.) we are enabled, as in the voltaic pile, to expand or convert the local action into a current, then chemical action can be traced through its variations to the production of all the phenomena of tension and the static state, these being in every respect the same as if the electric forces producing them had been developed by friction.

1739. It was Berzelius, I believe, who first spoke of the aptness of certain particles to assume opposite states when in presence of each other (959.). Hypothetically we may suppose these states to increase in intensity by increased approximation, or by heat, &c. until at a certain point combination occurs, accompanied by such an arrangement of the forces of the two particles between themselves as is equivalent to a discharge, producing at the same time a particle which is throughout a conductor (1700.).

1740. This aptness to assume an excited electrical state (which is probably polar in those forming non-conducting matter) appears to be a primary fact, and to partake of the nature of induction (1162.), for the particles do not seem capable of retaining their particular state independently of each other (1177.) or of matter in the opposite state. What appears to be definite about the particles of matter is their assumption of a particular state, as the positive or negative, in relation to each other, and not of either one or other indifferently; and also the acquirement of force up to a certain amount.

1741. It is easily conceivable that the same force which causes local action between two free particles shall produce current force if one of the particles is previously in combination, forming part of an electrolyte (923. 1738.). Thus a particle of zinc, and one of oxygen, when in presence of each other, exert their inductive forces (1740.), and these at last rise up to the point of combination. If the oxygen be previously in union with hydrogen, it is held so combined by an analogous exertion and arrangement of the forces; and as the forces of the oxygen and hydrogen are for the time of combination mutually engaged and related, so when the superior relation of the forces between the oxygen and zinc come into play, the induction of the former or oxygen towards the metal cannot be brought on and increased without a corresponding deficiency in its induction towards the hydrogen with which it is in combination (for the amount of force in a particle is considered as definite), and the latter therefore has its force turned towards the oxygen of the next particle of water; thus the effect may be considered as extended to sensible distances, and thrown into the condition of static induction, which being discharged and then removed by the action of other particles produces currents.

1742. In the common voltaic battery, the current is occasioned by the tendency of the zinc to take the oxygen of the water from the hydrogen, the effective action being at the place where the oxygen leaves the previously existing electrolyte. But Schoenbein has arranged a battery in which the effective action is at the other extremity of this essential part of the arrangement, namely, where oxygen goes to the electrolyte[A]. The first may be considered as a case where the current is put into motion by the abstraction of oxygen from hydrogen, the latter by that of hydrogen from oxygen. The direction of the electric current is in both cases the same, when referred to the direction in which the elementary particles of the electrolyte are moving (923. 962.), and both are equally in accordance with the hypothetical view of the inductive action of the particles just described (1740.).

[A] Philosophical Magazine, 1838, xii. 225, 315. also De la Rive's results with peroxide of manganese. Annales de Chimie, 1836, lxi. p. 40.--Dec. 1838.

1743. In such a view of voltaic excitement, the action of the particles may be divided into two parts, that which occurs whilst the force in a particle of oxygen is rising towards a particle of zinc acting on it, and falling towards the particle of hydrogen with which it is associated (this being the progressive period of the inductive action), and that which occurs when the change of association takes place, and the particle of oxygen leaves the hydrogen and combines with the zinc. The former appears to be that which produces the current, or if there be no current, produces the state of tension at the termination of the battery; whilst the latter, by terminating for the time the influence of the particles which have been active, allows of others coming into play, and so the effect of current is continued.

1744. It seems highly probable, that excitement by friction may very frequently be of the same character. Wollaston endeavoured to refer such excitement to chemical action[A]; but if by chemical action ultimate union of the acting particles is intended, then there are plenty of cases which are opposed to such a view. Davy mentions some such, and for my own part I feel no difficulty in admitting other means of electrical excitement than chemical action, especially if by chemical action is meant a final combination of the particles.

[A] Philosophical Transactions, 1801, p. 427.

1745. Davy refers experimentally to the opposite states which two particles having opposite chemical relations can assume when they are brought into the close vicinity of each other, but not allowed to combine[A]. This, I think, is the first part of the action already described (1743.); but in my opinion it cannot give rise to a continuous current unless combination take place, so as to allow other particles to act successively in the same manner, and not even then unless one set of the particles be present as an element of an electrolyte (923. 963.); i.e. mere quiescent contact alone without chemical action does not in such cases produce a current.

[A] Philosophical Transactions, 1807, p. 31.

1746. Still it seems very possible that such a relation may produce a high charge, and thus give rise to excitement by friction. When two bodies are rubbed together to produce electricity in the usual way, one at least must be an insulator. During the act of rubbing, the particles of opposite kinds must be brought more or less closely together, the few which are most favourably circumstanced being in such close contact as to be short only of that which is consequent upon chemical combination. At such moments they may acquire by their mutual induction (1740.) and partial discharge to each other, very exalted opposite states, and when, the moment after, they are by the progress of the rub removed from each other's vicinity, they will retain this state if both bodies be insulators, and exhibit them upon their complete separation.

1747. All the circumstances attending friction seem to me to favour such a view. The irregularities of form and pressure will cause that the particles of the two rubbing surfaces will be at very variable distances, only a few at once being in that very close relation which is probably necessary for the development of the forces; further, those which are nearest at one time will be further removed at another, and others will become the nearest, and so by continuing the friction many will in succession be excited. Finally, the lateral direction of the separation in rubbing seems to me the best fitted to bring many pairs of particles, first of all into that close vicinity necessary for their assuming the opposite states by relation to each other, and then to remove them from each other's influence whilst they retain that state.

1748. It would be easy, on the same view, to explain hypothetically, how, if one of the rubbing bodies be a conductor, as the amalgam of an electrical machine, the state of the other when it comes from under the friction is (as a mass) exalted; but it would be folly to go far into such speculation before that already advanced has been confirmed or corrected by fit experimental evidence. I do not wish it to be supposed that I think all excitement by friction is of this kind; on the contrary, certain experiments lead me to believe, that in many cases, and perhaps in all, effects of a thermo-electric nature conduce to the ultimate effect; and there are very probably other causes of electric disturbance influential at the same time, which we have not as yet distinguished.

_Royal Institution. June, 1838._

INDEX.

* * * * *

N.B. A dash rule represents the italics immediately preceding it. The references are sometimes to the individual paragraph, and sometimes to that in conjunction with those which follow.

* * * * *

Absolute charge of matter, 1169. ---- quantity of electricity in matter, 852, 861, 873. Acetate of potassa, its electrolysis, 749. Acetates, their electrolysis, 774. Acetic acid, its electrolysis, 773. Acid, nitric, formed in air by a spark, 324. ----, or alkali, alike in exciting the pile, 932. ----, transference of, 525. ---- for battery, its nature and strength, 1128, 1137. ---- ----, nitric, the best, 1138. ---- ----, effect of different strengths, 1139. ---- in voltaic pile, does not evolve the electricity, 925, 933. ---- ----, its use, 925. Acids and bases, their relation in the voltaic pile, 927, 933. Active battery, general remarks on, 1034, 1136. Adhesion of fluids to metals, 1038. Advantages of a new voltaic battery, 1132. Affinities, chemical, opposed voltaically, 891, 904, 910. ----, their relation in the active pile, 949. Air, its attraction by surfaces, 622. ----, charge of, 1173. ----, ----, by brush, 1434, 1441. ----, ----, by glow, 1537, 1543. ----, convective currents in, 1572, 1576, 1581. ----, dark discharge in, 1548. ----, disruptive discharge in, 1359, 1406, 1425, 1526. ----, induction in, 1208, 1215, 1284, 1362. ----, its insulating and conducting power, 411, 1332, 1336, 1362. ----, its rarefaction facilitates discharge, 1375. ----, electrified, 1443. ----, electro-chemical decompositions in, 454, 1623. ----, hot, discharges voltaic battery, 271, 274. ----, poles of, 455, 461, 559. ----, positive and negative brush in, 1467, 1472, 1476. ----, ---- glow in, 1526, 1530. ----, ---- spark in, 1485. ----, rarefied, brush in, 1451, 1456. ----, retention of electricity on conductors by, 1377, 1398. ----, specific inductive capacity of, 1284. ----, ----, not varied by temperature or pressure, 1287, 1288. Alkali has strong exciting power in voltaic pile, 884, 931, 941. ----, transference of, 525. Amalgamated zinc, its condition, 1000. ----, how prepared, 863. ----, its valuable use, 863, 999. ---- battery, 1001. Ammonia, nature of its electrolysis, 748. ----, solution of, a bad conductor, 554, 748. Ampere's inductive results, 78, 255, 379 note. Anions defined, 665, 824. ----, table of, 847. ---- related through the entire circuit, 963. ----, their action in the voltaic pile, 924. ----, their direction of transfer, 962, Anode defined, 663. Antimony, its relation to magneto-electric induction, 139. ----, chloride of, not an electrolyte, 690, 796. ----, oxide of, how affected by the electric current, 801. ---- supposed new protoxide, 693. ---- ----, sulphuret, 694. Animal electricity, its general characters considered, 351. ---- is identical with other electricities, 354, 360. ----, its chemical force, 355. ----, enormous amount, 359. ----, evolution of heat, 353, ----, magnetic force, 351. ----, physiological effects, 357. ----, spark, 358. ----, tension, 352. Apparatus, inductive, 1187. See Inductive apparatus. Arago's magnetic phenomena, their nature, 81, 120. ----, reason why no effect if no motion, 126, ----, direction of motion accounted for, 121. ----, due to induced electric currents, 119, 248. ----, like electro-magnetic rotations in principle, 121. ----, not due to direct induction of magnetism, 128, 138, 215, 243, 248. ----, obtained with electro-magnets, 129. ----, produced by conductors only, 130, 215. ----, time an element in, 124. ----, Babbage and Hershel's results explained, 127. Arago's experiment, Sturgeon's form of, 219. Associated voltaic circles, 989. Atmospheric balls of fire, 1611. ----, electricity, its chemical action, 336. Atomic number judged of from electrochemical equivalent, 851. Atoms of matter, 869, 1703. ----, their electric power, 856, 860. Attraction of particles, its influence in Doebereiner's phenomena, 619. Attractions, electric, their force, 1022 note. ----, chemic, produce current force, 852, 918, 947, 996, 1741. ----, ---- local force, 852, 921, 947, 959, 1739. ----, hygrometric, 621. Aurora borealis referred to magneto-electric induction, 192. Axis of power, the electric current on, 517, 1627, 1642.

Balls of fire, atmospheric, 1611. Barlow's revolving globe, magnetic effects explained, 137, 160. Barry, decomposed bodies by atmospheric electricity, 338. Bases and acids, their relation in the pile, 927. Battery, Leyden, that generally used, 291. Battery, voltaic, its nature, 856, 989. ----, origin of its power, 878, 989. ----, ---- not in contact, 887, 915, ----, ---- chemical, 879, 916, 919, 1741. ----, ----, oxidation of the zinc, 919, 944. ----, its circulating force, 858, 1120. ----, its local force, 1120. ----, quantity of electricity circulating, 990. ----, intensity of electricity circulating, 990, 993. ----, intensity of its current, 909, 994. ----, ---- increased, 905, 989. ----, its diminution in power, 1035. ----, ---- from adhesion of fluid, 1003, 1136. ----, ---- ---- peculiar state of metal, 1040. ----, ---- ---- exhaustion of charge, 1042. ----, ---- ---- irregularity of plates, 1045, 1146. ----, use of metallic contact in, 893, 896. ----, electrolytes essential to it, 921. ----, ----, why, 858, 923. ----, state of metal and electrolyte before contact, 916. ----, conspiring action of associated affinities, 989. ----, purity of its zinc, 1144. ----, use of amalgamated zinc in, 999. ----, plates, their number, 1151. ----, ---- size, 1154. ----, ---- vicinity, 1148. ----, ---- immersion, 1150. ----, ---- relative age, 1146. ----, ---- foulness, 1145. ----, excited by acid, 880, 926, 1137. ----, ---- alkali, 931, 934, 941. ----, ---- sulphuretted solutions, 943. ----, the acid, its use, 925, ----, acid for, 1128, 1137. ----, nitric acid best for, 1137. ----, construction of, 989, 1001, 1121. ----, with numerous alternations, 989. ----, Hare's, 1123. ----, general remarks on, 1031. 1136. ----, simultaneous decompositions with, 1156. ----, practical results with, 1136. ----, improved, 1001, 1006, 1120. ----, ----, its construction, 1124. ----, ----, power, 1125, 1128. ----, ----, advantages, 1132. ----, ----, disadvantages, 1132. Batteries, voltaic, compared, 1126. Becquerel, his important secondary results, 745, 784. Berzelius, his view of combustion, 870, 959. Biot's theory of electro-chemical decomposition, 486. Bismuth, its relation to magneto-electric induction, 139. Bodies classed in relation to the electric current, 823. ---- classed in relation to magnetism, 255. Bodies electrolyzable, 824. Bonijol decomposed substances by atmospheric electricity, 336. Boracic acid a bad conductor, 408. Brush, electric, 1425. ----, produced, 1425. ----, not affected by nature of conductors, 1454, 1473. ----, is affected by the dielectrics, 1455, 1463, 1475. ----, not dependent on current of air, 1440. ----, proves molecular action of dielectric, 1449, 1450. ----, its analysis, 1427, 1433. ----, nature, 1434, 1441, 1447. ----, form, 1428, 1449, 1451. ----, ramifications, 1439. ---- ----, their coalescence, 1453. ----, sound, 1426, 1431. ----, requisite intensity for, 1446. ---- has sensible duration, 1437. ---- is intermitting, 1427, 1431, 1451. ----, light of, 1444, 1445, 1451. ----, ----, in different gases, 1446, 1454. ----, dark? 1444, 1552. ----, passes into spark, 1448. ----, spark and glow relation of, 1533, 1539, 1542. ----, in gases, 1454, 1463, 1476. ----, oxygen, 1457, 1476. ----, nitrogen, 1458, 1476. ----, hydrogen, 1459, 1476. ----, coal-gas, 1460, 1476. ----, carbonic acid gas, 1461, 1476. ----, muriatic acid gas, 1462, 1476. ----, rare air, 1451, 1455, 1474. ----, oil of turpentine, 1452. ----, positive, 1455, 1467, 1484. ----, negative, 1468, 1472, 1484. ----, ----, of rapid recurrence, 1468, 1491. ----, positive and negative in different gases, 1455, 1475, 1506.

Capacity, specific inductive, 1252. ----. See Specific inductive capacity. Carbonic acid gas facilitates formation of spark, 1463. ----, brush in, 1461, 1476. ----, glow in, 1534. ----, spark in, 1422, 1463. ----, positive and negative brush in, 1476. ----, ---- discharge in, 1546. ----, non-interference of, 645, 652. Carbonic oxide gas, interference of, 645, 652. Carrying discharge, 1562. ----. See Discharge convective. Cathode described, 663, 824. Cations, or cathions, described, 665, 824. ----, table of, 817. ----, direction of their transfer, 962. Cations, are in relation through the entire circuit, 963. Characters of electricity, table of, 360. ---- the electric current, constant, 1618, 1627. ---- voltaic electricity, 268. ---- ordinary electricity, 284. ---- magneto-electricity, 343. ---- thermo-electricity, 349. ---- animal electricity, 351. Charge, free, 1684. ---- is always induction, 1171, 1177, 1300, 1682. ---- on surface of conductors: why, 1301. ----. influence of form on, 1302. ----, ---- distance on, 1303. ----, loss of, by convection, 1569. ----, removed from good insulators, 1203. ---- of matter, absolute, 1169. ---- of air, 1173. ---- ---- by brush, 1434, 1441. ---- ---- by glow, 1526, 1537, 1543. ---- of particles in air, 1564. ---- of oil of turpentine, 1172. ---- of inductive apparatus divided, 1208. ----, residual, of a Leyden jar, 1249. ----, chemical, for battery, good, 1137. -----, ----, weak and exhausted, 1042, 1143. Chemical action, the, exciting the pile is oxidation, 921. ---- superinduced by metals, 564. ---- ---- platina, 564, 617, 630. ---- tested by iodide of potassium, 315. Chemical actions, distant, opposed to each other, 891, 910, 1007. Chemical affinity influenced by mechanical forces, 656. ---- transferable through metals, 918. ---- statical or local, 852, 921, 917, 959. ---- current, 852, 918, 947, 996. Chemical decomposition by voltaic electricity, 278, 450, 661. ---- common electricity, 309, 453. ---- magneto-electricity, 346. ---- thermo-electricity, 349. ---- animal electricity, 355. ----. See Decomposition electro-chemical. Chemical and electrical forces identical, 877, 918, 947, 960, 965, 1031. Chloride of antimony not an electrolyte, 690. ---- lead, its electrolysis, 794, 815. ---- ----, electrolytic intensity for, 978. ---- silver, its electrolysis, 541, 813, 902. ---- ----, electrolytic intensity for, 979. ---- tin, its electrolysis, 789, 819. Chlorides in solution, their electrolysis, 766. ---- fusion, their electrolysis, 789, 813. Circle of anions and cathions, 963. Circles, simple voltaic, 875. ----, associated voltaic, 989. Circuit, voltaic, relation of bodies in, 962. Classification of bodies in relation to magnetism, 255. ---- the electric current, 823, 817. Cleanliness of metals and other solids, 633. Clean platina, its characters, 633, 717. ----, its power of effecting combination, 590, 605, 617, 632. ----, ----. See Plates of platina. Coal gas, brush in, 1460. ----, dark discharge in, 1556. ----, positive and negative brush in, 1476. ----, positive and negative discharge in, 1515. ----, spark in, 1422. Colladon on magnetic force of common electricity, 289. Collectors, magneto-electric, 86. Combination effected by metals, 564, 608. ---- solids, 564, 618. ---- poles of platina, 566. ---- platina, 564, 568, 571, 590, 630. ---- ----, as plates, 569. ---- ----, as sponge, 609, 636. ---- ----, cause of, 590, 616, 625, 656. ---- ----, how, 630. ---- ----, interferences with, 638, 652, 655. ---- ---- retarded by olefiant gas, 640. ---- ---- ---- carbonic oxide, 645, 652. ---- ---- ---- sulphuret of carbon, 650. ---- ---- ---- ether, 651. ---- ---- ---- other substances, 649, 653, 654. Comparison of voltaic batteries, 1126, 1146. Conditions, general, of voltaic decomposition, 669. ----, new, of electro-chemical decomposition, 453. Conducting power measured by a magnet, 216. ---- of solid electrolytes, 419. ---- of water, constant, 984. Conduction, 418, 1320. ----, its nature, 1320, 1326, 1611. ----, of two kinds, 987. ----, preceded by induction, 1329, 1332, 1338. ---- and insulation, cases of the same kind, 1320, 1326, 1336, 1338, 1561. ----, its relation to the intensity of the current conducted, 419. ---- common to all bodies, 444, 449. ---- by a vacuum, 1613. ---- by lac, 1234, 1324. ---- by sulphur, 1241, 1328. ---- by glass, 1239, 1324. ---- by spermaceti, 1240, 1323. ---- by gases, 1336. ----, slow, 1233, 1245, 1328. ---- affected by temperature, 445, 1339. ---- by metals diminished by heat, 432, 445. ---- increased by heat, 432, 441, 445. ---- of electricity and heat, relation of, 416. ----, simple, can occur in electrolytes, 967, 983. ----, ---- with very feeble currents, 970. ---- by electrolytes without decomposition, 968, 1017, 1032. ---- and decomposition associated in electrolytes, 413, 676, 854. ---- facilitated in electrolytes, 1355. ---- by water bad, 1159. ---- ---- improved by dissolved bodies, 984, 1355. ----, electrolytic, stopped, 380, 1358, 1705. ---- of currents stopped by ice, 381. ---- conferred by liquefaction, 394, 410. ---- taken away by solidification, 394, 1705. ---- ---- why, 910, 1705. ----, new law of, 380, 394, 410. ----, ----, supposed exception to, 691, 1340. ----, general results as to, 443. Conductive discharge, 1320. Conductors, electrolytic, 474. ----, magneto-electric, 86. ----, their nature does not affect the electric brush, 1454. ----, size of, affects discharge, 1372. ----, form of, affects discharge, 1374, 1425. ----, distribution of electricity on, 1368. ----, ----, affected by form, 1374. ----, ----, ---- distance, 1364, 1371. ----, ----, ---- air pressure, 1375. ----, ----, irregular with equal pressure, 1378. Constancy of electric current, 1618. Constitution of electrolytes as to proportions, 679, 697, 830, 1708. ---- liquidity, 394, 823. Contact of metals not necessary for electrolyzation, 879. ----, its use in the voltaic battery, 893. ---- not necessary for spark, 915, 956. Contiguous particles, their relation to induction, 1165, 1679. ---- active in electrolysis, 1349, 1703. Convection, 1562, 1642. ---- or convective discharge. See Discharge convective. Copper, iron, and sulphur circle, 943. Coruscations of lightning, 1464. Coulomb's electrometer, 1180. ----, precautions in its use, 1182, 1186, 1206. Crystals, induction through, 1689. Cube, large, electrified, 1173. Cubes of crystals, induction through, 1692, 1695. Current chemical affinity, 852, 918, 947, 996. Current, voltaic, without metallic contact, 879, 887. Current, electric, 1617. ----, defined, 282, 511. ----, nature of, 511, 667, 1617, 1627. ----, variously produced, 1618. ----, produced by chemical action, 879, 916, 1741. ----, ---- animals, 351. ----, ---- friction, 301, 307, 311. ----, ---- heat, 349, ----, ---- discharge of static electricity, 296, 307, 363. ----, ---- induction by other currents, 6, 1089. ----, ---- ---- magnets, 30, 88, 344. ----, evolved in the moving earth, 181. ----, in the earth, 187. ----, natural standard of direction, 663. ----, none of one electricity, 1627, 1632, 1635. ----, two forces everywhere in it, 1627, 1632, 1635, 1642. ----, one, and indivisible, 1627. ----, an axis of power, 517, 1642. ----, constant in its characters, 1618, 1627. ----, inexhaustibility of, 1631. ----, its velocity in conduction, 1648. ----, ---- electrolyzation, 1651. ----, regulated by a fine wire, 853, note. ----, affected by heat, 1637. ----, stopped by solidification, 381. ----, its section, 498, 504, 1634. ----, ---- presents a constant force, 1634. ----, produces chemical phenomena, 1621. ----, ---- heat, 1625. ----, its heating power uniform, 1630. ----, produces magnetism, 1653. ----, Porrett's effects produced by, 1646. ----, induction of, 1, 6, 232, 241, 1101, 1048. ----, ----, on itself, 1048. ----, ----. See Induction of electric current. ----, its inductive force lateral, 1108. ----, induced in different metals, 193, 213, 201, 211. ----, its transverse effects, 1653. ----, ---- constant, 1655. ----, its transverse forces, 1658. ----, ---- are in relation to contiguous particles, 1664. ----, ---- their polarity of character, 1665. ---- and magnet, their relation remembered, 38, note. Currents in air by convection, 1572, 1581. ----, metals by convection, 1603. ----, oil of turpentine by convection, 1595, 1598. Curved lines, induction in, 1215. Curves, magnetic, their relation to dynamic induction, 217, 232.

Daniell on the size of the voltaic metals, 1525. Dark discharge,1444, 1544. ----. See Discharge, dark. Dates of some facts and publications, 139, note after. Davy's theory of electro-chemical decomposition, 482, 500. ---- electro-chemical views, 965. ---- mercurial cones, convective phenomena, 1603. Decomposing force alike in every section of the current, 501, 505. ----, variation of, on each particle, 503. Decomposition and conduction associated in electrolytes, 413, 854. ----, primary and secondary results of, 742, 777. ---- by common electricity, 309, 454. ---- ----, precautions, 322. Decomposition, electro-chemical, 450, 669. ----, nomenclature of, 661. ----, new terms relating to, 662. ----, its distinguishing character, 309. ----, by common electricity, 309, 454. ----, by a single pair of plates, 862, 897, 904, 931. ----, by the electric current, 1621. ----, without metallic contact, 880, 882. ----, its cause, 891, 904, 910. ----, not due to direct attraction or repulsion of poles, 493, 497, 536, 542, 5460. ----, dependent on previous induction, 1345. ----, ---- the electric current, 493, 510, 524, 854. ----, ---- intensity of current, 905. ----, ---- chemical affinity of particles, 519, 525, 519. ----, resistance to, 891, 910, 1007. ----, intensity requisite for, 966, 1354. ----, stopped by solidification, 380, 1358, 1705. ----, retarded by interpositions, 1007. ----, assisted by dissolved bodies, 1355. ----, division of the electrolyte, 1347, 1623, 1701. ----, transference, 519, 525, 538, 550, 1347, 1706. ----, why elements appear at the poles, 535. ----, uncombined bodies do not travel, 544, 546. ----, circular series of effects, 562, 962. ----, simultaneous, 1156, ----, definite, 329, 372, 377, 504, 704, 714, 722, 726, 732, 764, 783, 807, 821, 960. ----, ---- independent of variations of electrodes, 714, 722, 807, 832. ----, necessary intensity of current, 911, 966, 1345, 1354. ----, influence of water in, 472. ----, in air, 451, 461, 469. ----, some general conditions of, 669. ----, new conditions of, 453. ----, primary results, 742. ----, secondary results, 702, 742, 748, 777. ----, of acetates, 774. ----, acetic acid, 773. ----, ammonia, 748. ----, chloride of antimony, 690, 796. ----, ---- lead, 794, 815. ----, ---- silver, 541, 813, 979. ----, chlorides in solution, 766. ----, ---- fusion, 789, 913. ----, fused electrolytes, 789. ----, hydriodic acid and iodides, 767, 787. ----, hydrocyanic acid and cyanides, 771. ----, hydrofluoric acid and fluorides, 770. ----, iodide of lead, 802, 818. ----, ---- potassium, 805. ----, muriatic acid, 758, 780. ----, nitre, 753. ----, nitric acid, 752. ----, oxide antimony, 801. ----, ---- lead, 797. ----, protochloride of tin, 789, 819. ----, protiodide of tin, 804. ----, sugar, gum, &c., 776. ----, of sulphate of magnesia, 495. ----, sulphuric acid, 757. ----, sulphurous acid, 755. ----, tartaric acid, 775. ----, water, 704, 785, 807. ----, theory of, 477, 1345. ----, ----, by A. de la Rive, 489, 507, 514, 543. ----, ----, Biot, 486. ----, ----, Davy, 482, 500. ----, ----, Grotthuss, 481, 499, 515. ----, ----, Hachette, 491, 513, ----, ----, Riffault and Chompre, 485, 507, 512. ----, author's theory, 518, 524, 1345, 1623, 1703, 1766. Definite decomposing action of electricity, 329, 372, 377, 504, 704, 783, 821. ----, magnetic action of electricity, 216, 362, 367, 377. ----, electro-chemical action, 822, 869, 960. ----, ----, general principles of, 822, 862. ----, ----, in chloride of lead, 815. ----, ----, ---- silver, 813. ----, ----, in hydriodic acid, 767, 787. ----, ----, iodide of lead, 802, 818. ----, ----, muriatic acid, 758, 786, ----, ----, protochloride of tin, 819. ----, ----, water, 732, 785, 807. Degree in measuring electricity, proposal for, 736. De la Rive on heat at the electrodes, 1637. ----, his theory of electro-chemical decomposition, 489, 507, 514, 543. Dielectrics, what, 1168. ----, their importance in electrical actions, 1666. ----, their relation to static induction, 1296. ----, their condition under induction, 1369, 1679. ----, their nature affects the brush, 1455. ----, their specific electric actions, 1296, 1398, 1423, 1454, 1503, 1560. Difference of positive and negative discharge, 1465, 1480, 1485. Differential inductometer, 1307. Direction of ions in the circuit, 962. ----, the electric current, 563. ----, the magneto-electric current, 114, 116. ----, the induced volta-electric current, 19, 26, 1091. Disruptive discharge, 1359, 1405. See Discharge, disruptive. Discharge, electric, as balls of fire, 1641. ----, of Leyden jar, 1300. ----, of voltaic battery by hot air, 271, 274. ----, ---- points, 272. ----, velocity of, in metal, varied, 1333. ----, varieties of, 1319. ----, brush, 1425. See Brush. ----, carrying, 1562. See Discharge, convective. ----, conductive, 1320. See Conduction. ----, dark, 1444, 1544. ----, disruptive, 1359, 1405. ----, electrolytic, 1343, 1622, 1704. ----, glow, 1526. See Glow. ----, positive and negative, 1465. ----, spark, 1406. See Spark, electric. Discharge, connective, 1442, 1562, 1601, 1623, 1633, 1642. ----, in insulating media, 1562, 1572. ----, in good conductors, 1603. ----, with fluid terminations in air, 1581, 1589. ----, ---- liquids, 1597. ----, from a ball, 1576, 1590. ----, influence of points in, 1573. ----, affected by mechanical causes, 1579. ----, ---- flame, 1580. ----, with glow, 1576. ----, charge of a particle in air, 1564. ----, ---- oil of turpentine, 1570. ----, charge of air by, 1442, 1592. ----, currents produced in air, 1572, 1581, 1591. ----, ---- oil of turpentine, 1595, 1598. ----, direction of the currents, 1599, 1645. ----, Porrett's effects, 1646, ----, positive and negative, 1593, 1600, 1643. ----, related to electrolytic discharge, 1622, 1633. Discharge, dark, 1444, 1544, 1560. ----, with negative glow, 1544. ----, between positive and negative glow, 1547. ----, in air, 1548. ----, muriatic acid gas, 1554. ----, coal gas, 1556. ----, hydrogen, 1558. ----, nitrogen, 1559. Discharge, disruptive, 1405. ----, preceded by induction, 1362. ----, determined by one particle, 1370, 1409. ----, necessary intensity, 1409, 1553. ----, determining intensity constant, 1410. ----, related to particular dielectric, 1503. ----, facilitates like action, 1417, 1435, 1453, 1553. ----, its time, 1418, 1436, 1498, 1641. ----, varied by form of conductors, 1302, 1372, 1374. ----, ---- change in the dielectric, 1395, 1422,1454. ----, ---- rarefaction of air, 1365, 1375, 1451. ----, ---- temperature, 1367, 1380. ----, ---- distance of conductors, 1303, 1364, 1371. ----, ---- size of conductors, 1372. ----, in liquids and solids, 1403. ----, in different gases, 1381, 1388, 1421. ----, ---- not alike, 1395. ----, ---- specific differences, 1399, 1422, 1687. ----, positive and negative, 1393, 1399, 1465, 1524. ----, ----, distinctions, 1467, 1475, 1482. ----, ----, differences, 1485, 1501. ----, ----, relative facility, 1496, 1520. ----, ----, dependent on the dielectric, 1503. ----, ----, in different gases, 1506, 1510, 1518, 1687. ----, ----, of voltaic current, 1524. ----, brush, 1425. ----, collateral, 1412. ----, dark, 1444, 1544, 1560. ----, glow, 1526. ----, spark, 1406. ----, theory of, 1308, 1406, 1434. Discharge, electrolytic, 1164, 1343, 1621, 1703, 1706. ----, previous induction, 1345, 1351. ----, necessary intensity, 912, 966, 1346, 1354. ----, division of the electrolyte, 1347, 1704. ----, stopped by solidifying the electrolyte, 380, 1358, 1705. ----, facilitated by added bodies, 1355. ----, in curved lines, 521, 1216, 1351. ----, proves action of contiguous particles, 1349. ----, positive and negative, 1525. ----, velocity of electric current in, 1650. ----, related to convective discharge, 1622. ----, theory of, 1344, 1622, 1704. Discharging train generally used, 292. Disruptive discharge, 1405. See Discharge, disruptive. Dissimulated electricity, 1684. Distance, its influence in induction, 1303, 1364,1371. ---- over disruptive discharge, 1364, 1371. Distant chemical actions, connected and opposed, 891, 909. Distinction of magnetic and magneto-electric action, 138, 215, 243, 253. Division of a charge by inductive apparatus, 1208. Doebereiner on combination effected by platina, 609, 610. Dulong and Thenard on combination by platina and solids, 609, 611. Dust, charge of its particles, 1567.

Earth, natural magneto-electric induction in, 181, 190, 192. Elasticity of gases, 626. ---- gaseous particles, 658. Electric brush, 1425. See Brush, electric. ---- condition of particles of matter, 862, 1669. ---- conduction, 1320. See Conduction. ---- current defined, 283, 511. ---- ----, nature of, 511, 1617, 1627. ---- ----. See Current, electric. ---- ----, induction of, 6, 232, 241, 1048, 1101. See Induction of electric current. ---- ----, ----, on itself, 1048. ---- discharge, 1319. See Discharge. ---- force, nature of, 1667. See Forces. ---- induction, 1162. See Induction. ---- inductive capacity, 1252. See Specific inductive capacity. ---- polarity, 1685. See Polarity, electric. ---- spark, 1406. See Spark, electric. ---- and magnetic forces, their relation, 118, 1411, 1653, 1658, 1709, 1731. Electrics, charge of, 1171, 1247. Electrical excitation, 1737. See Excitation. ---- machine generally used, 290. ---- battery generally used, 291. ---- and chemical forces identical, 877, 917, 947, 960, 965, 1031. Electricities, their identity, however excited, 265, 360. ----, one or two, 516, 1667. ----, two, 1163. ----, ----, their independent existence, 1168. ----, ----, their inseparability, 1168, 1177, 1244. ----, ----, never separated in the current, 1628. Electricity, quantity of, in matter, 852, 861. ----, its distribution on conductors, 1368. ----, ---- influenced by form, 1302, 1374. ----, ---- ---- distance, 1303, 1364, 1371. ----, ---- ---- air's pressure, 1375. ----, relation of a vacuum to, 1613. ----, dissimulated, 1684. ----, common and voltaic, measured, 361, 860. ----, its definite decomposing action, 329, 377, 783, 1621. ----, ---- heating action, 1625. ----, ---- magnetic action, 216, 366. ----, animal, its characters, 351. ----, magneto-, its characters, 343. ----, ordinary, its characters, 284. ----, thermo-, its characters, 349. ----, voltaic, its characters, 268. Electricity from magnetism, 27, 36, 57, 83, 135, 140. ----, on magnetisation of soft iron by currents, 27, 34, 57, 113. ---- ---- magnets, 36, 44. ----, employing permanent magnets, 39, 84, 112. ----, ---- terrestrial magnetic force, 140, 150, 161. ----, ---- moving conductors, 55, 83, 132, 139, 149, 161, 171. ----, ---- ---- essential condition, 217. ---- by revolving plate, 83, 149, 240. ---- ---- a constant source of electricity, 89, 90, 154. ---- ----, law of evolution, 114. ---- ----, direction of the current evolved, 91, 99, 110, 116, 117. ---- ----, course of the currents in the plate, 123, 150. ---- by a revolving globe, 137, 160. ---- by plates, 94, 101. ---- by a wire, 49, 55, 109, 112, 137. ----, conductors and magnet may move together, 218. ----, current produced in a single wire, 49, 55, 170. ----, ---- a ready source of electricity, 46, note. ----, ---- momentary, 28, 30, 47. ----, ---- permanent, 89, 154. ----, ---- deflects galvanometer, 30, 39, 46. ----, ---- makes magnets, 34. ----, ----, shock of, 56. ----, ----, spark of, 32. ----, ---- traverses fluids, 23, 33. ----, ----, its direction, 30, 38, 41, 52, 53, 54, 78, 91, 99, 114, 142, 166, 220, 222. ----, effect of approximation and recession, 18, 39, 50. ----, the essential condition, 217. ----, general expression of the effects, 256. ----, from magnets alone, 220. Electricity of the voltaic pile, 875. ---- its source, 875. ---- ---- not metallic contact, 887, 915. ---- ---- is in chemical action, 879, 916, 919, 1738, 1741. Electro-chemical decomposition, 450, 661. ----, nomenclature, 661. ----, general conditions of, 669. ----, new conditions of, 453, ----, influence of water in, 472. ----, primary and secondary results, 742. ----, definite, 732, 783. ----, theory of, 477. ----. See also Decomposition, electrochemical. Electro-chemical equivalents, 824, 833, 835, 855. ----, table of, 847. ----, how ascertained, 837. ---- always consistent, 835. ---- same as chemical equivalents, 836, 839. ---- able to determine atomic number, 851. Electro-chemical excitation, 878, 919, 1738. Electrode defined, 662. Electrodes affected by heat, 1637. ----, varied in size, 714, 722. ----, ---- nature, 807. ----. See Poles. Electrolysis, resistance to, 1007. Electrolyte defined, 664. ---- exciting, solution of acid, 881, 925. ---- ---- alkali, 931, 941. ---- exciting, water, 944, 945. ---- ---- sulphuretted solution, 943. Electrolytes, their necessary constitution, 669, 823, 829, 858, 921, 1347, 1708. ---- consist of single proportionals of elements, 679, 697, 830, 1707. ---- essential to voltaic pile, 921. ---- ----, why, 858, 923. ---- conduct and decompose simultaneously, 413. ---- can conduct feeble currents without decomposition, 967. ----, as ordinary conductors, 970, 983, 1344. ----, solid, their insulating and conducting power, 419. ----, real conductive power not affected by dissolved matters, 1356. ----, needful conducting power, 1158. ---- are good conductors when fluid, 394, 823. Electrolytes non-conductors when solid 381, 394. ----, why, 910, 1705. ----, the exception, 1032. Electrolytes, their particles polarize as wholes, 1700. ----, polarized light sent across, 951. ----, relation of their moving elements to the passing current, 923, 1704. ----, their resistance to decomposition, 891, 1007, 1705. ----, and metal, their states in the voltaic pile, 946. ----, salts considered as, 698. ----, acids not of this class, 681. Electrolytic action of the current, 478, 518, 1620. ---- conductors, 474. ---- discharge, 1343. See Discharge, electrolytic. ---- induction, 1164, 1343. ---- intensity, 911, 966, 983. ---- ---- varies for different bodies, 912, 986, 1354. ---- ---- of chloride of lead, 978. ---- ---- chloride of silver, 979. ---- ---- sulphate of soda, 975. ---- ---- water, 968, 981. ---- ---- its natural relation, 987. Electrolyzation, 450, 661, 1164, 1347, 1704. See Decomposition electro-chemical. ---- defined, 664. ---- facilitated, 394, 417, 549, 1355. ---- in a single circuit, 863, 879. ----, intensity needful for, 919, 966, ---- of chloride of silver, 541, 979. ---- sulphate of magnesia, 495. ---- and conduction associated, 413, 676. Electro-magnet, inductive effects in, 1060. Electro-magnetic induction definite, 216, 366. Electrometer, Coulomb's, described, 1180. ----, how used, 1183. Electro-tonic state, 60, 231, 242, 1114, 1661, 1729. ---- considered common to all metals, 66. ---- ---- conductors, 76. ---- is a state of tension, 71. ---- is dependent on particles, 73. Elementary bodies probably ions, 849. Elements evolved by force of the current, 493, 520, 524. ---- at the poles, why, 535. ---- determined to either pole, 552, 681, 757. ----, transference of, 454, 538. ----, if not combined, do not travel, 544, 546. Equivalents, electro-chemical, 824, 833, 855. ----, chemical and electro-chemical, the same, 836, 839. Ether, interference of, 651. Evolution of electricity, 1162, 1737. ---- of one electric force impossible, 1175. ---- of elements at the poles, why, 535. Excitation, electrical, 1737. ---- by chemical action, 878, 916, 1739. ---- by friction, 1744. Exclusive induction, 1681.

Flame favours convectivc discharge, 1580. Flowing water, electric currents in, 190. Fluid terminations for convection, 1581. Fluids, their adhesion to metals, 1038. Fluoride of lead, hot, conducts well, 1340. Force, chemical, local, 947, 959, 1739. ----, circulating, 917, 947, 996, 1120. Force, electric, nature of, 1163, 1667. ----, inductive, of currents, its nature, 60, 1113, 1735. Forces, electric, two, 1163. ----, inseparable, 1163, 1177, 1244, 1627. ---- and chemical, are the same, 877, 916. ---- and magnetic, relation of, 1411, 1653, 1658, 1709. ---- ----, are they essentially different? 1663, 1731. Forces, exciting, of voltaic apparatus, 887, 916. ----, exalted, 905, 994, 1138, 1148. Forces, polar, 1665. ---- of the current, direct, 1620. ---- ----, lateral or transverse, 1653, 1709. Form, its influence on induction, 1302, 1374. ---- discharge, 1372, 1374. Fox, his terrestrial electric currents, 187. Friction electricity, its characters, 284. ----, excitement by, 1744. Fusion, conduction consequent upon, 394, 402. Fusinieri, on combination effected by platina, 613.

Galvanometer, affected by common electricity, 289, 366. ----, a correct measure of electricity, 367, note. Gases, their elasticity, 626, 657. ----, conducting power, 1336. ----, insulating power, 1381, 1507. ----, ---- not alike, 1395, 1508. ----, specific inductive capacity, 1283, 1290. ----, ---- alike in all, 1292. ----, specific influence on brush and spark, 1463, 1687. ----, discharge, disruptive, through, 1381. ----, brush in, 1454. ----, spark in, 1421. ----, positive and negative brushes in, 1475. ----, ----, their differences, 1476. ----, positive and negative discharge in, 1393, 1506, 1687. ----, solubility of, in cases of electrolyzation, 717, 728. ----, from water, spontaneous recombination of, 566. ----, mixtures of, affected by platina plates, 571. ----, mixed, relation of their particles, 625. General principles of definite electrolytic action, 822. ---- remarks on voltaic batteries, 1031, 1136. ---- results as to conduction, 443. ---- ---- induction, 1295. Glass, its conducting power, 1239. ----, its specific inductive capacity, 1271. ----, its attraction for air, 622. ----, ---- water, 1251. Globe, revolving of Barlow, effects explained, 137, 160. ----, is magnetic, 164. Glow, 1405, 1525. ----, produced, 1527. ----, positive, 1527. ----, negative, 1530. ----, favoured by rarefaction of air, 1529. ----, is a continuous charge of air, 1526, 1537, 1543. ----, occurs in all gases, 1534. ----, accompanied by a wind, 1535. ----, its nature, 1543, ----, discharge, 1526. ----, brush and spark relation of, 1533, 1538, 1539, 1542. Grotthuss' theory of electro-chemical decomposition, 481, 499, 515. Growth of a brush, 1437. ---- spark, 1553.

Hachette's view of electro-chemical decomposition, 491. Hare's voltaic trough, 1123, 1132. Harris on induction in air, 1363. Heat affects the two electrodes, 1637. ---- increases the conducting power of some bodies, 432, 438, 1340. ----, its conduction related to that of electricity, 416. ----, as a result of the electric current, 853, note, 1625, 1630. ---- evolved by animal electricity, 353. ---- ---- common electricity, 287. ---- ---- magneto-electricity, 344. ---- ---- thermo-electricity, 349. ---- ---- voltaic electricity, 276. Helix, inductive effects in, 1061, 1094. Hydriodic acid, its electrolyses, 767, 787. Hydrocyanic acid, its electrolyses, 771, 788. Hydrofluoric acid, not electrolysable, 770. Hydrogen, brush in, 1459. ----, positive and negative brush in, 1476. ----, ---- discharge in, 1514. Hydrogen and oxygen combined by platina plates, 570, 605. ---- spongy platina, 609.

Ice, its conducting power, 419. ---- a non-conductor of voltaic currents, 381. Iceland crystal, induction across, 1695. Identity, of electricities, 265, 360. ---- of chemical and electrical forces, 877, 917, 947, 961, 1031. Ignition of wire by electric current, 853, note, 1630. Improved voltaic battery, 1006, 1120. Increase of cells in voltaic battery, effect of, 990. Inducteous surfaces, 1483. Induction apparatus, 1187. ----, fixing the stem, 1190, 1193, 1200. ----, precautions, 1194, 1199, 1213, 1232, 1250. ----, removal of charge, 1203. ----, retention of charge, 1205, 1207. ----, a charge divided, 1208. ----, peculiar effects with, 1233. Induction, static, 1161. ----, an action of contiguous particles, 1165, 1231, 1253, 1295, 1450, 1668, 1679. ----, consists in a polarity of particles, 1298, 1670, 1679. ----, continues only in insulators, 1298, 1324, 1338. ----, intensity of, sustained, 1362. ----, influenced by the form of conductors, 1302. ----, ---- distance of conductors, 1303. ----, ---- relation of the bounding surfaces, 1483. ----, charge, a case of, 1171, 1177, 1300. ----, exclusive action, 1681. ----, towards space, 1614. ----, across a vacuum, 1614. ---- through air, 1217, 1284. ---- ---- different gases, 1381, 1395. ---- ---- crystals, 1689, ---- ---- lac, 1228, 1255, 1308. ---- ---- metals, 1329, 1332. ---- ---- all bodies, 1331, 1334. ----, its relation to other electrical actions, 1165, 1178. ----, ---- insulation, 1324, 13602, 1368, 1678. ----, ---- conduction, 1320. ----, ---- discharge, 1319, 1323, 1362. ----, ---- electrolyzation, 1164, 1343. ----, ---- intensity, 1178, 1362. ----, ---- excitation, 1178, 1740. ----, its relation to charge, 1177, 1299. ---- an essential general electric function, 1178, 1299. ----, general results as to, 1295. ----, theory of, 1165, 1231, 1295, 1667, 1669. ---- in curved lines, 1166, 1215, 1679. ---- ----, through air, 1218, 1449. ---- ----, ---- other gases, 1226. ---- ----, ---- lac, 1228. ---- ----, ---- sulphur, 1228. ---- ----, ---- oil of turpentine, 1227. induction, specific, 1167, 1252, 1307. ----, the problem stated, 1252. ----, ---- solved, 1307. ----, of air, 1284. ----, ----, invariable, 1287, 1288. ----, of gases, 1283, 1290. ----, ---- alike in all, 1292. ----, of shell-lac, 1256, 1269. ----, glass, 1271. ----, sulphur, 1275. ----, spermaceti, 1279. ----, certain fluid insulators, 1280. Induction of electric currents, 6, 34, 232, 241, 1048, 1089, 1101, 1660, 1718. ----, on aiming the principal current, 10, 238, 1101. ----, on stopping the principal current, 10, 17, 238, 1087, 1100. ---- by approximation, 18, 236. ---- by increasing distance, 19, 237. ---- effective through conductors, 1719, 1721, 1735. ---- ---- insulators, 1719, 1722, 1735. ---- in different metals, 193, 202, 211, 213. ---- in the moving earth, 181. ---- in flowing water, 190. ---- in revolving plates, 85, 240. ----, the induced current, its direction, 26, 232. ----, ---- duration, 19, 47, 89. ----, ----, traverses fluids, 20, 23. ----, ----, its intensity in different conductors, 183, 193, 201, 211, 213. ----, ----, not obtained by Leyden discharge, 24. ----, Ampere's results, 78, 255, 379, note. Induction of a current on itself, 1048, 1109. ----, apparatus used, 1052. ----, in a long wire, 1064, 1068, 1092, 1118. ----, ---- doubled wire, 1096. ----, ---- helix, 1053, 1061. ---- in doubled helices, 1096. ---- in an electro-magnet, 1056, 1060. ----, wire and helix compared, 1065. ----, short wire, effects with, 1067. ----, action momentary, 1070, 1091, 1100. ----, causes no permanent change in the current, 1071. ----, not due to momentum, 1077. ----, induced current separated, 1078, 1089. ----, effect at breaking contact, 1060, 1081, 1084, 1087. ----, ---- making contact, 1101, 1106. ----, effects produced, shock, 1060, 1064, 1079. ----, ---- spark, 1060, 1064, 1080. ----, ---- chemical decomposition, 1084. ----, ---- ignition of wire, 1081, 1104. ----, cause is in the conductor, 1059, 1070. ----, general principles of the action, 1093, 1107. ----, direction of the forces lateral, 1108. induction, magnetic, 255, 1658, 1710. ----, by intermediate particles, 1663, 1710, 1729, 1735. ----, through quiescent bodies, 1712, 1719, 1720, 1735. ----, ---- moving bodies, 1715, 1716, 1719. ---- and magneto-electric, distinguished, 138, 215, 243, 253. Induction, magneto-electric, 27, 58, 81, 140, 193, 1709. See Arago's magnetic phenomena. ----, magnelectric, 58. ----, electrolytic, 1164, 1345, 1702, 1740. ----, volta-electric, 26. Inductive capacity, specific, 1167, 1252. Inductive force of currents lateral, 26, 1108. ----, its nature, 1113, 1660, 1663, 1709. Inductive force, lines of, 1231, 1297, 1304. ----, often curved, 1219, 1224, 1230. ----, exhibited by the brush, 1449. ----, their lateral relation, 1231, 1297, 1304. ----, their relation to magnetism, 1411, 1658, 1709. Inductometer, differential, 1307, 1317. Inductric surfaces, 1483. Inexhaustible nature of the electric current, 1631. Inseparability of the two electric forces, 1163, 1177, 1244, 1628. Insulating power of different gases, 1388, 1395, 1507. Insulation, 1320, 1359, 1361. ----, its nature, 1321. ---- is sustained induction, 1324. ----, degree of induction sustained, 1362. ---- dependent on the dielectrics, 1368. ---- ---- distance in air, 1303, 1364, 1371. ---- ---- density of air, 1365, 1375. ---- ---- induction, 1368. ---- ---- form of conductors, 1302, 1374. ----, as affected by temperature of air, 1367, 1380. ---- in different gases, 1381, 1388. ---- ---- differs, 1395. ---- in liquids and solids, 1403. ---- in metals, 1328, 1331, 1332. ---- and conduction not essentially different, 1320, 1326, 1336, 1338, 1561. ----, its relation to induction, 1324, 1362, 1368, 1678. Insulators, liquid, good, 1172. ----, solid, good, 1254. ----, the best conduct, 1233, 1241, 1245, 1247, 1254. ---- tested as to conduction, 1255. ---- and conductors, relation of, 1328, 1334, 1338. Intensity, its influence in conduction, 419. ----, inductive, how represented, 1370. ----, relative, of magneto-electric currents, 183, 193, 211, 213. ---- of disruptive discharge constant, 1410. ----, electrolytic, 912, 966, 983, 1354. ---- necessary for electrolyzation, 911, 966. ---- of the current of single circles, 904. ---- ---- increased, 906. ---- of electricity in the voltaic battery, 990, 993. ---- of voltaic current increased, 906, 990. Interference with combining power of platina, 638, 655. ---- by olefiant gas, 640. ---- carbonic oxide, 645. ---- sulphuret of carbon, 650. ---- ether, 651. Interpositions, their retarding effects, 1018. Iodides in solution, their electrolysis, 769. ---- fusion, their electrolysis, 802, 813. Iodide of lead, electrolysed, 802, 818. ---- of potassium, test of chemical action, 316. Ions, what, 665, 824, 833, 834, 849. ---- not transferable alone, 542, 547, 826. ----, table of, 847. Iron, both magnetic and magneto-electric at once, 138, 254. ----, copper and sulphur circles, 943.

Jenkin, his shock by one pair of plates, 1049.

Kemp, his amalgam of zinc, 999. Knight, Dr. Gowin, his magnet, 44.

Lac, charge removed from, 1203. ----, induction through, 1255. ----, specific inductive capacity of, 1256, 1269. ----, effects of its conducting power, 1234. ----, its relation to conduction and insulation, 1324. Lateral direction of inductive forces of currents, 26, 1108. ---- forces of the current, 1653, 1709. Law of conduction, new, 380, 394, 410. ---- magneto-electric induction, 114. ---- volta-electric induction, 26. Lead, chloride of, electrolysed, 794, 815. ----, fluoride of, conducts well when heated, 1340. ----, iodide of, electrolysed, 802, 818. ----, oxide of, electrolysed, 797. Leyden jar, condition of its charge, 1682. ----, its charge, nature of, 1300. ----, its discharge, 1300. ----, its residual charge, 1249. Light, polarized, passed across electrolytes, 951. ----, electric, 1405, 1445, 1560, note. ----, ----, spark, 1406, 1553. ----, ----, brush, 1425, 1444, 1445. ----, ----, glow, 1526. Lightning, 1420, 1404, 1641. Lines of inductive force, 1231, 1304, ---- often curved, 1219, 1224, 1230. ----, as shown by the brush, 1449. ----, their lateral relation, 1231, 1297, 1304. ----, their relation to magnetism, 1411, 1658, 1709. Liquefaction, conduction consequent upon, 380, 394, 410. Liquid bodies which are non-conductors, 405. Local chemical affinity, 947, 959, 961, 1739.

Machine, electric, evolution of electricity by, 1748. ------, magneto-electric, 135, 154, 158, 1118. Magnelectric induction, 58. ----, collectors or conductors, 86. Magnesia, sulphate, decomposed against water, 494, 533. ----, transference of, 495. Magnet, a measure of conducting power, 216. ---- and current, their relation remembered, 38, note. ---- ---- plate revolved together, 218. ---- ---- cylinder revolved together, 219. ---- revolved alone, 220, 223. ---- and moving conductors, their general relation, 256. ---- made by induced current, 13, 14. ----, electricity from, 36, 220, 223. Magnetic bodies, but few, 255. ----, curves, their inductive relation, 217, 232. ---- effects of voltaic electricity, 277. ---- ---- common electricity, 288, 367. ---- ---- magneto-electricity, 27, 83, 345. ---- ---- thermo-electricity, 349. ---- ---- animal electricity, 354. ---- and electric forces, their relation, 118, 1411, 1653, 1658, 1709, 1731. ---- forces active through intermediate particles, 1663, 1710, 1729, 1735. ---- forces of the current, 1653. ---- ---- very constant, 1654. ---- deflection by common electricity, 289, 296. ---- phenomena of Arago explained, 81. ---- induction. See Induction, magnetic. ---- induction through quiescent bodies, 1712, 1719, 1720, 1735. ---- ---- moving bodies, 1715, 1719. ---- and magneto-electric action distinguished, 138, 215, 243, 253. Magnetism, electricity evolved by, 27. ----, its relation to the lines of inductive force, 1411, 1658, 1709. ---- bodies classed in relation to, 255. Magneto-electric currents, their intensity, 183, 193, 211, 213. ----, their direction, 114, 110. ---- traverse fluids, 33. ---- momentary, 30. ---- permanent, 89. ---- in all conductors, 193, 213. Magneto-electric induction, 27, 58. ----, terrestrial, 110, 181. ----, law of, 114. ----. See Arago's magnetic phenomena. Magneto-electric machines, 135, 154, 158. ----, inductive effects in their wires, 1118, Magneto-electricity, its general characters considered, 343, &c. ---- identical with other electricities, 360. ----, its tension, 343. ----, evolution of heat, 344. ----, magnetic force, 345. ----, chemical force, 346. ----, spark, 348. ----, physiological effects, 347. ----. See Induction, magnetic. Matter, atoms of, 869, 1703. ----, new condition of, 60, 231, 242, 1114, 1661, 1729. ----, quantity of electricity in, 852, 861, 873, 1652. ----, absolute charge of, 1169. Measures of electricity, galvanometer, 367, note. ----, voltameter, 704, 736, 739. ----, metal precipitated, 740, 842. Measure of specific inductive capacity, 1307, 1600. Measurement of common and voltaic electricities, 361, 860, 1652. ---- electricity, degree, 736, 738. ---- ---- by voltameter, 704, 736, 739. ---- ---- by galvanometer, 367, note. ---- ---- by metal precipitated, 740, 842. Mechanical forces affect chemical affinity, 656. Mercurial terminations for convection, 1581. Mercury, periodide of, an exception to the law of conduction? 691, 1341. ----, perchloride of, 692, 1341. Metallic contact not necessary for electrolyzation, 879. ---- not essential to the voltaic current, 879, 887, 915. ---- its use in the pile, 893, 896. Metallic poles, 557. Metal and electrolyte, their state, 946. Metals, adhesion of fluids to, 1038. ----, their power of inducing combination 564, 608. ----, ---- interfered with, 638. ----, static induction in, 1329, 1332. ----, different, currents induced in, 193, 211. ----, generally secondary results of electrolysis, 746. ---- transfer chemical force, 918. ----, transference of, 539, 545. ---- insulate in a certain degree, 1328. ----, convective currents in, 1603. ----, but few magnetic, 255. Model of relation of magnetism and electricity, 116. Molecular inductive action, 1164, 1669. Motion essential to magneto-electric induction, 39, 217, 256. ---- across magnetic curves, 217. ---- of conductor and magnet, relative, 114. ---- ---- not necessary, 218. Moving magnet is electric, 220. Muriatic acid gas, its high insulating power, 1395. ----, brush in, 1462. ----, dark discharge in, 1554. ----, glow in, 1534. ----, positive and negative brush in, 1476. ----, spark in, 1422, 1463. ----, ----, has no dark interval, 1463, 1555. Muriatic acid decomposed by common electricity, 314. ----, its electrolysis (primary), 758, 786.

Nascent state, its relation to combination, 658, 717. Natural standard of direction for current, 663. ---- relation of electrolytic intensity, 987. Nature of the electric current, 1617. ---- force or forces, 1667. Negative current, none, 1627, 1632. ---- discharge, 1465, 1484. ---- ----, as Spark, 1467, 1482. ---- ----, as brush, 1466, 1502. ---- spark or brush, 1484, 1502. Negative and positive discharge, 1465, 1482, 1525 ---- in different gases, 1393. New electrical condition of matter, 60, 231, 242, 1114, 1661, 1729. ---- law of conduction, 380, 394, 410. Nitric acid formed by spark in air, 324. ---- favours excitation of current, 906, 1138 ---- ---- transmission of current, 1020. ---- is best for excitation of battery, 1137. ----, nature of its electrolysis, 752. Nitrogen determined to either pole, 554, 748, 752. ---- a secondary result of electrolysis, 746, 748. ----, brush in, 1458. ----, dark discharge in, 1559. ----, glow in, 1534. ----, spark in, 1422, 1463. ----, positive and negative brush in, 1476. ----, ---- discharge in, 1512. ----, its influence on lightning, 1464. Nomenclature, 662, 1483. Nonconduction by solid electrolytes, 381, 1358, 1705. Note on electrical excitation, 1737. Nuclei, their action, 623, 657.

Olefiant gas, interference of, 610, 652. Ordinary electricity, its tension, 285. ---- evolution of heat, 287. ---- magnetic force, 288, 362. ---- chemical force, 309, 454. ---- ----, precautions, 322. ---- spark, 333. ---- physiological effect, 332. ---- general characters considered, 284. ----, identity with other electricities, 360. Origin of the force of the voltaic pile, 878, 910, 919. Oxidation the origin of the electric current in the voltaic pile, 919, 930. Oxide of lead electrolysed, 797. Oxygen, brush in, 1457. ----, positive and negative brush in, 1476, ----, ---- discharge in, 1513. ----, solubility of, in cases of electrolyzation, 717, 728. ----, spark in, 1422. ---- and hydrogen combined by platina plates, 570, 605, 630. ---- ---- spongy platina, 609, 636. ---- ---- other metals, 608.

Particles, their nascent state, 658. ---- in air, how charged, 1564. ----, neighbouring, their relation to each other, 619, 624, 657. ----, contiguous, active in induction, 1165, 1677. ---- of a dielectric, their inductive condition, 1369, 1410, 1669. ----, polarity of, when under induction, 1298, 1676. ----, how polarised, 1669, 1679. ----, ----, in any direction, 1689. ----, ----, as wholes or elements, 1699. ----, ----, in electrolytes, 1702. ----, crystalline, 1689. ----, contiguous, active in electrolysis, 1349, 1702. ----, their action in electrolyzation, 520, 1343, 1703. ----, ---- local chemical action, 961, 1739. ----, ---- relation to electric action, 73. ----, ---- electric action, 1669, 1679, 1740. Path of the electric spark, 1107. Phosphoric acid not an electrolyte, 682. Physiological effects of voltaic-electricity, 279. ---- common electricity, 332. ---- magneto-electricity, 56, 347. ---- thermo-electricity, 349. ---- animal electricity, 357. Pile, voltaic, electricity of, 875. ----. See Battery, voltaic. Plates of platina effect combination, 568, 571, 590, 630. ---- prepared by electricity, 570, 585, 588. ---- ---- friction, 591. ---- ---- heat, 595. ---- ---- chemical cleansing, 599, 605, ----, clean, their general properties, 633, 717. ----, their power preserved, 576. ----, ---- in water, 580. ----, their power diminished by action, 581. ----, ---- exposure to air, 636. ----, their power affected by washing in water, 582. ----, ---- heat, 584, 597. ----, ---- presence of certain gases, 638, 655. ----, their power, cause of, 590, 616, 630. ----, theory of their action, Doebereiner's, 610. ----, ----, Dulong and Thenard's, 611. ----, ----, Fusinieri's, 613. ----, ----, author's, 619, 626, 630, 656. Plates of voltaic battery foul, 1145. ----, new and old, 1116. ----, vicinity of, 1148. ----, immersion of, 1003, 1150. ----, number of, 989, 1151. ----, large or small, 1154. Platina, clean, its characters, 633, 717. ---- attracts matter from the air, 634. ----, spongy, its state, 637. ----, clean, its power of effecting combination, 564, 590, 605, 617, 630. ----, ---- interfered with, 638. ----, its action retarded by olefiant gas, 640, 652. ----, ----, carbonic oxide, 645, 652. ----. See Combination, Plates of platina, and Interference. ---- poles, recombination effected by, 567, 588. Plumbago poles for chlorides, 794. Poisson's theory of electric induction, 1305. Points, favour convective discharge, 1573. ----, fluid for convection, 1581. Polar forces, their character, 1665. ---- decomposition by common electricity, 312, 321, 469. Polarity, meaning intended, 1304, 1685. ---- of particles under induction, 1298, 1676. ----, electric, 1070, 1085. ----, ----, its direction, 1688, 1703, ----, ----, its variation, 1687. ----, ----, its degree, 1686. ----, ----, in crystals, 1689. ----, ----, in molecules or atoms, 1699. ----, ----, in electrolytes, 1702. Polarized light across electrolytes, 951. Poles, electric, their nature, 461, 498, 556, 662. ----, appearance of evolved bodies at, accounted for, 535. ---- one element to either? 552, 681, 757. ----, of air, 455, 461, 559. ----, of water, 491, 558. ----, of metal, 557. ----, of platina, recombination effected by, 567, 588. ----, of plumbago, 794. Poles, magnetic, distinguished, 44, note. Porrett's peculiar effects, 1646. Positive current none, 1627, 1632. ---- discharge, 1465, 1480. ---- ----, as spark, 1467, 1482. ---- ----, as brush, 1467, 1476. ---- spark or brush, 1484, 1502. ---- and negative, convective discharge, 1600. ---- ---- disruptive discharge, 1465, 1482, 1485, 1525. ---- ---- ---- in different gases, 1393. ---- ---- voltaic discharge, 1524. ---- ---- electrolytic discharge, 1525. Potassa acetate, nature of its electrolysis, 749. Potassium, iodide of, electrolysed, 805. Power of voltaic batteries estimated, 1126. Powers, their state of tension in the pile, 949. Practical results with the voltaic battery, 1136. Pressure of air retains electricity, explained, 1377, 1398. Primary electrolytical results, 742. Principles, general, of definite electrolytic action, 822. Proportionals in electrolytes, single, 679, 697.

Quantity of electricity in matter, 852, 861, 873, 1652. ---- voltaic battery, 990.

Rarefaction of air facilitates discharge, why, 1375. Recombination, spontaneous, of gases from water, 566. Relation, by measure, of electricities, 361. ---- of magnets and moving conductors, 256. ---- of magnetic induction to intervening bodies, 1662, 1728. ---- of a current and magnet, to remember, 38, note. ---- of electric and magnetic forces, 118, 1411, 1653, 1658,1709, 1731. ---- of conductors and insulators, 1321, 1326, 1334, 1338. ---- of conduction and induction, 1320, 1337. ---- of induction and disruptive discharge, 1362. ---- ---- electrolyzation, 1164, 1343. ---- ---- excitation, 1178, 1740. ---- ---- charge, 1171, 1177, 1300. ---- of insulation and induction, 1324, 1362, 1368, 1678. ----, lateral, of lines of inductive force, 1231, 1297, 1304. ---- of a vacuum to electricity, 1613. ---- of spark, brush, and glow, 1533, 1539, 1542. ---- of gases to positive and negative discharge, 1510. ---- of neighbouring particles to each other, 619, 624. ---- of elements in decomposing electrolytes, 923, 1702. ---- ---- exciting electrolytes, 921. ---- of acids and bases voltaically, 927, 933. Remarks on the active battery, 1034, 1136. Residual charge of a Leyden jar, 1249. Resistance to electrolysis, 891, 904, 911, 1007. ---- of an electrolyte to decomposition, 1007. Results of electrolysis, primary or secondary, 742, 777. ----, practical, with the voltaic battery, 1136. ----, general, as to induction, 1295, 1669. Retention of electricity by pressure of the atmosphere explained, 1377, 1398. Revolving plate. See Arago's phenomena. ---- globe, Barlow's, effect explained, 137, 160, 169. ---- ----, magnetic, 164. ---- ----, direction of currents in, 161, 166. Riffault's and Chompre's theory of electro-chemical decomposition, 485, 507, 512. Rock crystal, induction across, 1692. Room, insulated and electrified, 1173. Rotation of the earth a cause of magneto-electric induction, 181.

Salts considered as electrolytes, 698. Scale of electrolytic intensities, 912. Secondary electrolytical results, 702, 742, 748, 777. ---- become measures of the electric current, 843. Sections of the current, 498, 1634. ----, decomposing force alike in all, 501, 1621. Sections of lines of inductive action, 1369. ----, amount of force constant, 1369. Shock, strong, with one voltaic pair, 1049. Silver, chloride of, its electrolyzation, 541, 813, 902. ----, electrolytic intensity for, 979. Silver, sulphuret of, hot, conducts well, 433. Simple voltaic circles, 875. ----, decomposition effected by, 897, 904, 931. Single and many pairs of plates, relation of, 990. Single voltaic circuits, 875. ---- without metallic contact, 879. ---- with metallic contact, 893. ---- their force exalted, 906. ---- give strong shocks, 1049. ---- ---- a bright spark, 1050. Solid electrolytes are non-conductors, 394, 402, 1358. ----, why, 910, 1705. Solids, their power of inducing combination, 564, 618. ---- interfered with, 638. Solubility of gases in cases of electrolyzation, 717, 728. Source of electricity in the voltaic pile, 875. ---- is chemical action, 879, 916, 919, 1741. Spark, 1360, 1406. Spark, electric, its conditions, 1360, 1406, 1553. ---- path, 1407. ---- light, 1553. ---- insensible duration or time, 1438. ---- accompanying dark parts, 1547, 1632. ---- determination, 1370. 1409. Spark is affected by the dielectrics, 1395, 1421. ---- size of conductor, 1372. ---- form of conductor, 1302, 1374. ---- rarefaction of air, 1375. Spark, atmospheric or lightning, 1464, 1641. ----, negative, 1393, 1467, 1482, 1484, 1502. ----, positive, 1393, 1448, 1467, 1482, 1484, 1502. ----, ragged, 1420, 1448. ----, when not straight, why, 1568. ----, variation in its length, 1381. ----, tendency to its repetition, 1392. ----, facilitates discharge, 1417, 1553. ----, passes into brush, 1448. ----, preceded by induction, 1362. ----, forms nitric acid in air, 324. ----, in gases, 1383, 1421. ----, in air, 1422. ----, in nitrogen, 1422, 1463. ----, in oxygen, 1422. ----, in hydrogen, 1422. ----, in carbonic acid, 1422, 1463. ----, in muriatic acid gas, 1422, 1463. ----, in coal-gas, 1422. ----, in liquids, 1424. ----, precautions, 958, 1074. ----, voltaic, without metallic contact, 915, 956. ---- from single voltaic pair, 1050. ---- from common and voltaic electricity assimilated, 334. ----, first magneto-electric, 32. ---- of voltaic electricity, 280. ---- of common electricity, 333. ---- of magneto-electricity, 348. ---- of thermo-electricity, 349. ---- of animal electricity, 358. ----, brush and glow related, 1533, 1539, 1542. Sparks, their expected coalition, 1412. Specific induction. See Induction, specific, 1252. Specific inductive capacity, 1252. ----, apparatus for, 1187. ---- of lac, 1256, 1270, 1308. ---- of sulphur, 1275, 1310. ---- of air, 1284. ---- of gases, 1283, 1290. ---- of glass, 1271. Spermaceti, its conducting power, 1240, 1323. ----, its relation to conduction and insulation, 1322. Standard of direction in the current, 663. State, electrotonic, 60, 231, 242, 1114, 1661, 1729. Static induction. See Induction, static. Sturgeon, his form of Arago's experiment, 249. ----, use of amalgamated zinc by, 863, 999. Sulphate of soda, decomposed by common electricity, 317. ----, electrolytic intensity for, 975. Sulphur determined to either pole, 552, 681, 757. ----, its conducting power, 1241, 1245. ----, its specific inductive capacity, 1275. ----, copper and iron, circle, 943. Sulphuret of carbon, interference of, 650. ---- silver, hot, conducts well, 433. Sulphuretted solution excites the pile, 943. Sulphuric acid, conduction by, 409, 681. ----, magneto-electric induction on, 200, 213. ---- in voltaic pile, its use, 925. ---- not an electrolyte, 681. ----, its transference, 525. ----, its decomposition, 681, 757. Sulphurous acid, its decomposition, 755. Summary of conditions of conduction, 443. ---- molecular inductive theory, 1669.

Table of discharge in gases, 1388. ---- electric effects, 360. ---- electro-chemical equivalents, 847. ---- electrolytes affected by fusion, 402. ---- insulation in gases, 1388. ---- ions, anions, and cathions, 847. Tartaric acid, nature of its electrolysis, 775. Tension, inductive, how represented, 1370. ---- of voltaic electricity, 268. ---- of common electricity, 285. ---- of thermo-electricity, 349. ---- of magneto-electricity, 343. ---- of animal electricity, 352. ---- of zinc and electrolyte in the voltaic pile, 949. Terrestrial electric currents, 187. Terrestrial magneto-electric induction, 140. ---- cause of aurora borealis, 192. ----, electric currents produced by, 141, 150. ----, ----, in helices alone, 148. ----, ----, ---- with iron, 141, 146. ----, ----, ---- with a magnet, 147. ----, ---- a single wire, 170. ----, ---- a revolving plate, 149. ----, ---- a revolving ball, 160. ----, ---- the earth, 173. Test between magnetic and magneto-electric action, 215, 243. Theory of combination of gases by clean platina, 619, 626, 630, 656. ---- electro-chemical decomposition, 477, 661, 1623, 1704. ---- the voltaic apparatus, 875, 1741. ---- static induction, 1165, 1231, 1295, 1666, 1667. ---- disruptive discharge, 1368, 1406, 1434. ---- Arago's phenomena, 120. Thermo-electricity, its general characters, 349. ---- identical with other electricities, 360. ----, its evolution of heat, 349. ----, magnetic, force, 349. ----, physiological effects, 349. ----, spark, 349. Time, 59, 68, 124, 1248, 1328, 1346, 1418, 1431, 1436, 1439, 1612, 1641, 1730. Tin, iodide of, electrolysed, 804. ----, protochloride, electrolysis of, definite, 789, 819. Torpedo, nature of its electric discharge, 359. ----, its enormous amount of electric force, 359. Transfer of elements and the current, their relation, 923, 962. Transference is simultaneous in opposite directions, 542, 828. ----, uncombined bodies do not travel, 544, 546, 826. ---- of elements, 454, 507, 539, 550, 826. ---- ---- across great intervals, 455, 468. ---- ----, its nature, 519, 525, 538, 549. ---- of chemical force, 918. Transverse forces of the current, 1653, 1709. Travelling of charged particles, 1563. Trough, voltaic. See Battery, voltaic. Turpentine, oil of, a good fluid insulator, 1172. ----, its insulating power destroyed, 1571. ---- charged, 1172. ----, brush in, 1452, ----, electric motions in, 1588, 1595, ----, convective currents in, 1595, 1598.

Unipolarity, 1635.

Vacuum, its relation to electricity, 1613. Vaporization, 657. Velocity of conduction in metals varied, 1333. ---- the electric discharge, 1641, 1649. ---- conductive and electrolytic discharge, difference of, 1650. Vicinity of plates in voltaic battery, 1148. Volta-electric induction, 26. Volta-electrometer, 704, 736. ----, fluid decomposed in it, water, 706, 728, 732. ----, forms of, 707, 734. ---- tested for variation of electrodes, 714, 722. ---- ---- fluid within, 727. ---- ---- intensity, 723. ----, strength of acid used in, 728,733. ----, its indications by oxygen and hydrogen, 736. ----, ---- hydrogen, 734. ----, ---- oxygen, 735. ----, how used, 737. Voltameter, 704. Voltaic battery, its nature, 875, 989. ----, remarks on, 1034, 1136. ----, improved, 1001, 1119. ----, practical results with, 1136. ----. See Battery, voltaic. Voltaic circles, simple, 875. ----, decomposition by, 897. Voltaic circles associated, or battery, 989. Voltaic circuit, relation of bodies in, 962. ----, defined, 282, 511. ----, origin of, 916, 1741. ----, its direction, 663, 925, ----, intensity increased, 905, 990. ----, produced by oxidation of zinc, 919, 930. ---- not due to combination of oxide and acid, 925, 933. ----, its relation to the combining oxygen, 921, 962. ----, ---- combining sulphur, 943. ----, ---- the transferred elements, 923, 962. ----, relation of bodies in, 962. Voltaic current, 1617. See Current, electric. Voltaic discharge, positive and negative, 1524. Voltaic decomposition, 450, 600. See Decomposition, electro-chemical. Voltaic electricity, identical with electricity, otherwise evolved, 268, 360. ----, discharged by points, 272. ----, ---- hot air, 271, 274. ----, its tension, 268, 275. ----, evolution of heat by, 276. ----, its magnetic force, 277. ----, its chemical force, 278. ----, its spark, 280. ----, its physiological effects, 279. ----, its general characters considered, 268. Voltaic pile distinguished, 856, note. ----, electricity of, 875. ----, depends on chemical action, 872. ----, relation of acid and bases in the, 927. ----. See Battery, voltaic. Voltaic spark without contact, 915, 956. ----, precautions, 958, 1074. Voltaic trough, 989. See Battery, voltaic.

Water, flowing, electric currents in, 190. ----, retardation of current by, 1159. ----, its direct conducting power, 1017, 1159, 1355. ----, ---- constant, 984. ----, electro-chemical decomposition against, 494, 532. ----, poles of, 494, 533, 558. ----, its influence in electro-chemical decomposition, 472. ---- is the great electrolyte, 924. ----, the exciting electrolyte when pure, 944. ----, ---- acidulated, 880, 926, 1137. ----, ---- alkalized, 931, 934, 941. ----, electrolytic intensity for, 968, 981, 1017. ---- electrolyzed in a single circuit, 862. ----, its electrolysis definite, 732, 785, 807. ----, decomposition of by fine wires, 327. ----, quantity of electricity in its elements, 853, 861. ----, determined to either pole, 553. Wheatstone's analysis of the electric brush, 1427. ---- measurement of conductive velocity in metals, 1328. Wire, ignition of, by the electric current, 853, note, 1631. ---- is uniform throughout, 1630. Wire a regulator of the electric current, 853, note. ----, velocity of conduction in, varied, 1333. ----, single, a current induced in, 170. ----, long, inductive effects in, 1064, 1118. Wollaston on decomposition by common electricity, 309. ---- decomposition of water by points, 327.

Zinc, amalgamated, its condition, 863, 1000. ----, used in pile, 999. Zinc, how amalgamated, 863. ----, of troughs, its purity, 1144. ----, its relation to the electrolyte, 949. ----, its oxidation is the source of power in the pile, 919. ---- plates of troughs, foul, 1145. ---- ----, new and old, 1146. ----, waste of, in voltaic batteries, 997.

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