English domestic clocks

Front matter

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Preface

Q¥JHIS book was written, primarily, to supplement another work, English Furniture of the Eighteenth Century, in the first volume of which certain chapters were devoted to long-case and bracket clocks, considered in the usual progression of English furniture types of the period. The larger book had the benefit of the examples of furniture of the various periods illustrated therein, which could be used for reference and comparison, an advantage obviously absent in the present work, which is concerned solely with clocks. On the other hand, this drawback is partly, if not wholly, compensated for by the greater space available, allowing of the treatment of the subject in fuller detail, and the fact that the shortcomings of the larger book were useful in showing what to amplify and what to avoid. It was felt, at the time, that the clock chapters in Fxglish Furniture of the Eighteenth Century were not only incomplete, but also inaccurate in many points of detail, and as theories were built on many of these imperfect premises, these theories were necessarily faulty in a corresponding degree. Some of the conclusions, and one of the chapters, that on ‘‘Chippendale and Sheraton Clockcases,’’ in the former book, have been adopted with little or no alteration in the present one. It may be remarked that some of the theories ventured at that time have been substantiated by the examination of the examples of clocks which have since been added to the specimens then illustrated. The association of authorship was rendered advisable by the fact that to properly describe the later examples (which are exclusive to this book), it was necessary to thoroughly examine the works of each clock, as many of the peculiarities which are invaluable in estimating the age of each example are not apparent in the photographs of case or dial. This examination was, obviously, the province of the practical clockmaker; hence the dual authorship.

It would appear, at first sight, that the student of the clock fashions of the period from 1665 to the present day is greatly assisted by the preserved records of the old clockmakers, and especially by the researches or lists of makers first made by Octavius Morgan and published in the /owrna/ of the Archeological Institution, afterwards in Wood’s Curzoszties of Watches and Clocks, 1866, in Some Account of the Clockmakers Company by Atkins and Overall in 1881, and recently by Mr. F. J. Britten.

This is undoubtedly true on a large degree, and we must acknowledge our large

3033599 indebtedness to Mr. Britten. When we have to consider exact periods of semidecades, however, the extant records become very meagre, and have to be examined very closely and received very cautiously. Many of the old clockmakers had a very extended business career, and it is often a nice point to determine exactly at which point a particular specimen should be assigned. The clock itself is the only really reliable criterion, as there is no doubt that many of the long-case clocks which are met with are not in their original cases; at any rate, this point has always to be reckoned with. Bracket clocks are, as a rule, free from this doubt, but the bracket clocks of the one maker are little or no guide in determining the characteristics of his long clocks, both as regards cases and movements. The reference ‘here to records” only "covers*= those” instancesmwheressthem date ouerne connection of a maker with the Clockmakers’ Company has been preserved. The assigning of a date to a maker from a single specimen of his work is obviously a matter of mere opinion.

An attempt has been made in this book to systematise the subject of English domestic clocks, and to avoid thereby, as far as possible, the discursiveness so common in books dealing with the technical side of our national handicrafts. If the volume does no more than to present, in interesting and readable form, the history of the development of perhaps the most characteristic of our national industries of the later seventeenth and the whole of the eighteenth centuries, and to promote an intelligent interest in the finer examples of the art of the clockmaker which are still available, it will not have been written quite in vain. These old clocks have a dual interest, as specimens of the skill of the cabinetmaker and the inventive ability of the clockmaker, and it is hardly fair to the latter to consider his productions merely as more or less decorative pieces of furniture, especially as many of the more notable examples are characterised by the extreme simplicity of their cases.

In conclusion, we desire to express our acknowledgments to Mr. Percy Webster, whose advice on many occasions has been invaluable, and whose knowledge on the subject of English clocks stands unrivalled at the present day ; and to Mr. Richard Hoffmann, who has kindly verified the mathematical calculations contained in this book.

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XV.

Contents

PREFACE

- THE PROBLEM OF THE MEASUREMENT OF TIME sLHES LAW OF THE PENDULUM

7 THE MECHANISM OF CLOCKS

Chapter I

The Problem of the Measurement of Time yom|ANY have been the devices, during the historical epoch of civilised g f man, for subdividing and recording the two motions of the earth: on its diurnal axial rotation and its orbital revolution round the sun.

Ce >) These time-recording instruments may be roughly divided into two U>sy GZ—| classes: the passive and the active. The sun-dial is the type of the former, the clock that of the latter. On the one, the sun does its own recording, as it were, indicating its position in the heavens by the line of shadow cast by the gnomen of the dial. In the other, a force is stored, by the winding ofa spring, the pulling up of a weight, or by any other contrivances, which force is released in regular fashion, so that the clock hand, or other indicator, will travel a given distance in a certain invariable time. The various methods of attaining this result do not concern us here at present, but it may be advisable to examine the nature of the attempt, and to see how much is based on natural periods and how much is purely arbitrary.

It is obvious that the subdivision of the day into twenty-four hours, of each hour into sixty minutes, and of each minute into sixty seconds, is an empirical one. It is not so obvious, however, that the calendar year of 365 days and the day itself are also not fixed astronomical periods, marking exactly the time taken by the earth to accomplish its orbital and axial revolutions respectively. The hour hand of a clock takes the same time—or should—to accomplish its path round the circle of the dial in June as in December; the length of the day—that is, the axial revolution of the earth—varies. The clock indicates approximately mean time—that is, an average for all the year; the sun-dial shows apparent solar time. Let us see how and why these differ.

The earth makes one axial revolution in 23 hours, 56 minutes,. 4.09 seconds; the clock subdivides a day of 24 hours. Twelve o’clock noon, as indicated by the clock, should be the moment when the position of the earth were such that the sun appeared to be directly overhead. This moment would be the same on each day had the earth no other motion. But we know that it has an orbital revolution round the sun, and therefore the position of the earth in relation to that of the sun cannot be exactly the same on successive days, and the sun, in describing

EX its apparent arc across the heavens, will reach the zenith sometimes before twelve o'clock noon, as marked by the clock, and sometimes later. The maximum variation each way is roughly about 15 minutes, or, to put it into exact figures, from 16 minutes 18 seconds before, to 14 minutes 28 seconds after, twelve o’clock mean time. The progression from the maximum before to the maximum after twelve o'clock is also not uniform, the problem being complicated by such factors as the inclination of the earth’s axis to the plane of the ecliptic, the perturbation of its orbital path round the sun, caused by the attractions of the moon, Venus, and Jupiter (and, in an infinitesimal degree, by that of Mars), the circular movement of the pole of the earth round | that of the ecliptic (known as precession), and the fact that the earth's motion round the sun is not at a uniform rate, being greater in December, when the earth is close to the sun, than in July when it is the farthest away.

In the same way as the sidereal day differs from the mean solar day, so does the year vary in like manner, and according to the standard of measurement adopted. Thus the tropical, or, as it is often incorrectly called, the solar year, is the measure of time which elapses from the appearance of the sun on one of the tropics to its return to the same position, and has a mean length of 365.2422414 mean solar days, or 365 days, 5 hours, 48 minutes, 49.7 seconds. From its historical and legal recognition as the common measure of time, this is also known as the civil year. The sidereal year is the period required by the sun to move from a given star to the same star again, and this year, affected as it is only by nutation (the oscillatory motion of the earth’s axis which disturbs the circular movement known as precession), is one of the most invariable quantities in the realm of astronomy, and has a mean value of 365.2563612 mean solar days, or 365 days, 6 hours, 9g minutes, 9.6 seconds. The anomalistic year is the time which elapses between the earth’s arrival at its perihelion (the point when it is the nearest to the sun) and its return to the same position. This is equivalent to 365.2595981 mean solar days, or 365 days, 6 hours, 13 minutes,

49.3 seconds.

The actual length of the day is also not a fixed quantity, owing to the moon’s attraction causing tides on the earth, the effect of which is to act as a constant brake on the axial rotation. The day is thus becoming gradually longer and longer.

It follows, therefore, from the foregoing, that there exists no fixed unit of measurement by which the length of the day or the year may be determined. Nothing is constant, and consequently no system of recording or subdividing can be even approximately correct. The clockmaker is concerned with the length of the day, and recognising that this is not an uniform quantity, he takes an approximate time from meridian to meridian, which he subdivides into 24 hours, each hour into 60 minutes, and each minute into 60 seconds. He may further subdivide the second in like manner, but these subdivisions are all arbitrary, depending upon an empirical day of uniform duration. It is his business to devise an instrument for recording these arbitrary divisions in an invariable way, so that the duration of his hours, minutes, and seconds shall remain always constant. He has to contend with natural forces, with heat and cold, which, in contracting and expanding the materials which he uses, affect his regulation, and cause his timekeepers to vary. In the constant struggle with nature he is continually being worsted, but the margin of error is steadily reduced after each encounter. The perfect timepiece will probably never be constructed, but it is a part of the purpose of this book to illustrate the later stages of this warfare between the forces of nature and the inventive ability of the maker of clocks, and at the same time to show the structural and ornamental evolution of the cases in which the clocks were enshrined, and of the dials, hands, and other embellishments of the clocks themselves.

Chapter II The Law of the Pendulum gJHE history of the development of the English domestic clock practically begins with the pendulum as a regulator, and with the power obtained by the fall of a weight, although the spring barrel is almost, if not quite, co-incidental with the weight-driven clock.!

Some exceptions must be made to the pendulum control in the rare cases of the ‘“‘balance wheel”: regulation; but these ican sbesdeicrredstoma later stage, when the mechanism of the earliest bracket clocks will be considered and examples illustrated. The ‘‘foliot” balance can be disregarded altogether, as this is never found in English clocks. For the present we can give our undivided attention to the pendulum clock, and it is curious that although nearly everyone is well acquainted with the pendulum, the laws affecting its operation are very little understood. We can therefore commence with the following quotation from Sir Robert Ball’s Story of the F/eavens, the Astronomer Royal of Ireland being a master of the art of lucid explanation of an abstruse subject.

‘‘For its journey to and fro the pendulum requires a certain amount of time, which does not appreciably depend upon the length of the circular arc through which the pendulum swings. To verify this law we suspend another pendulum beside the first, both being of the same length. If we draw both pendulums aside and then release them, they swing together and return together. This might have been expected. But if we draw one pendulum a great deal to one side, and the other only a little, the two pendulums still swing sympathetically. This, perhaps, would not have been expected. Try it again, with even a still greater difference in the arc of vibration, and still we see the two weights occupy the same time for the swing. We can vary the experiment in another way. Let us change the weights on the pendulums, so that they are of unequal size though both of iron. Shall we find any difference in the periods of vibration? We try again: the period is the same as before; swing them through different arcs, large or small, the period is still the same. But it may be said that this is due to the fact that both weights are of the same material. Try it again using a leaden weight instead

* The few rare spring-driven clocks engraved with English names which one meets of date prior to 1650 are invariably of foreign character. The early iron or brass wall clocks of unmistakable English origin are always weight-driven.

of one of the iron weights; the result is identical. Even with a ball of wood the period of oscillation is the same as with the ball of iron, and this is true no matter what be the arc through which the vibration takes place.

‘‘ Tf, however, we change the length of the wire by which the weight is supported, then the period will not remain unchanged. This can be very easily illustrated. Take a short pendulum with a wire only one-fourth of the length of that of the long one; suspend the two close together, and compare the periods of vibration of the short pendulum with that of the long one, and we find that the former has a period of only half that of the latter. We may state the result generally, and say that the time of the vibration of a pendulum is proportional to the square root of its length. If we quadruple the length of the suspending cord, we double the time of its vibration; if we increase the length of the pendulum ninefold, we increase the period of its vibration threefold.

‘‘It is the gravitation of the earth which makes the pendulum swing. The greater the attraction, the more rapidly will the pendulum oscillate. This may be easily accounted for. If the earth pulls the weight down very vigorously, the time will be short; if the power of the earth’s attraction be lessened, then it cannot pull the weight down so quickly, and the period will be lengthened.”’

It follows, as a necessary deduction from the above, that a clock pendulum swinging through its arc once in the space of a second must be, and can only be, of one given length. With a period of half a second the length is only one quarter that of the seconds’ pendulum. Stated in actual figures, in inches and fractions of inches, a pendulum with a period of swing of 1 second must have a length of 2.4462 inches; with a swing of 4 second, 9.7848 inches; 1 second, Borgo smlicics wei. e second, 61.155) Inches; 14 second, 88.0632 inches; and 2 seconds, 156,5572 inches.

The period of oscillation’ varies, however, at different parts of the globe, according to the proximity to the pole or the equator, being longer at the latter and shorter at the former, and it is even slightly altered if the pendulum be taken much below the surface of the earth, as, for example, down a coal-mine. Temperature also affects the time of swing of the ordinary clock pendulum, and this in a twofold way. In the first case the resistance of the atmosphere is lessened, and the time in consequence slightly shortened, if the air be heated; whereas, as an irregular compensation, heat expands, and lengthens the metal of which the pendulum rod is made, and thus protracts the time of the swing.

Ie

Quoting again from Sir Robert Ball :—

‘‘Tt is possible to determine the time of vibration of the pendulum with great accuracy. Let it swing for 10,000 oscillations, and measure the time that these oscillations have consumed. The arc through which the pendulum swings may not have remained quite constant, but this does not appreciably affect the ¢2me of its oscillation. Suppose that an error of a second is made in the determination of the time of 10,000 oscillations: this will only entail an error of the ten-thousandth part of a second in the time of a single oscillation, and will afford a correspondingly accurate determination of the gravity.

‘““Take a pendulum to the equator. Let it perform 10,000 oscillations, and determine carefully the ¢zme that these oscillations have required. Bring the same pendulum to another part of the earth, and repeat the experiment. We have thus a means of comparing the gravitation at the two places. There are, no doubt, a multitude of precautions to be observed, which need not here concern us. It is not necessary to enter into details as to the manner in which the motion of the pendulum is to be sustained, nor as to the effect of changes of temperature in the alteration of its length. It will suffice for us to see how the time of the pendulum’s swing can be measured accurately, and how from that measurement the intensity of the gravitation can be calculated.

‘““The pendulum thus enables us to make a gravitational survey of the surface of the earth with the highest degree of accuracy. We cannot, however, infer that gravity alone affects the oscillations of the pendulum. We have seen how the earth rotates on its axis, and we have attributed the bulging of the earth at the equator to this influence. But the centrifugal force arising from the rotation has the effect of decreasing the apparent weight of bodies, and the change is the greatest at the equator, and lessens gradually as we approach the poles. From this cause alone the attraction of the pendulum at the equator is less than elsewhere, and therefore the oscillations of the pendulum will take a longer time there than at other localities. A part of the apparent change in gravitation is accordingly due to the centrifugal force; but there is, in addition, a real alteration. At a hasty glance it might be thought that, as there was a protuberance of matter at the equator, there ought to be a greater attraction there than elsewhere. This is not so. The effect of the additional matter is more than compensated by the greater distance of the pendulum from the centre of the earth. Indeed, a moment's reflection will show that the pendulum at the pole is, on the whole, nearer to the mass of the earth than when it is at the equator. It illustrates, in a marked way, how the researches in different branches of science are interwoven, when we find that, by observing the swing of a pendulum at different parts of the earth, we are enabled to determine the safe of our globe as accurately as by the elaborate measurements of the arcs of the meridian.”

As the period of swing of a clock pendulum varies at different latitudes, it is necessary to qualify, somewhat, the foregoing statements regarding the different lengths for the various periods. To be exact, a pendulum with a swing of 1 second must have a length of 39.1393 inches, zz the latitude of London, but this measurement would vary at other parallels, being its longest at the pole, where the greater attraction causes the clock to go more quickly, and the shortest. at the equator. The famous clockmaker John Ellicott devised an instrument for calculating the effective lengths of pendulums at different parallels of latitude from equator to pole.

With a seconds’ pendulum, the clock simply records the number of the oscillations in terms of seconds, minutes, and hours. The power stored in the wound-up weight or spring is used merely to keep the pendulum swinging. Remove the weights, or allow the spring to run down, and the are of swing will gradually lessen until the pendulum ceases to oscillate. Gravitation has overcome the initial impetus civen’ to it. In a general way, the size of the weights or the power of the spring will not affect the time of the pendulum’s swing; it will cause it to describe a wider or narrower arc; but, as we have Seen, this does snotmaliectathe speriodicy time. “Actually, a’ very wide= arc of swing will affect the time slightly, owing to the increased resistance of the atmosphere. There are other considerations which have also to be taken into account with a pendulum driven by power. An _ over-weighted or over-sprung clock is said to ‘‘govern the pendulum,” instead of the pendulum governing the clock. The power exerted should be just sufficient to keep the pendulum at its work, no more nor less.

It is misleading, and hardly correct, to regard a pendulum as regulating a clock, as the inference is that the clock records the time and the pendulum causes it to do this in a regular fashion, which is only approximately true. Really, it is the pendulum which actually marks the time, which is _ recorded in terms of single swings and multiples of such on the dial of the clock.

If the clock goes, and fails to keep accurate time, it is always the pendulum

17 Cc which is at fault, never the clock itself if it be properly constructed. We are so generally accustomed to regard a clock dial as a circle on which is recorded the lapse of hours—twelve or twenty-four, according to the way in which the dial is divided—which for greater convenience is subdivided into minutes or seconds. The tendency to consider a clock in this way is even greater in the case of the early lantern or sheepshead types, where minute hands are exceptional or unknown. As a matter of fact, this way of regarding a clock is really beginning from the wrong end. What the clock actually does is to maintain a power sufficient to keep the pendulum on the swing, and to record the number of the oscillations. What we mean when we speak of a clock keeping time is that the pendulum swings once in a certain invariable fraction of the total length of the horological day of twenty-four hours, which, as we have seen in the first chapter, is the nearest we can get to a natural period of time, as distinct from an empirical one, such as a week, an hour, a minute, or a second. Thus the pendulum of a clock with a seconds’ dial oscillates 86,400 times in the 24-hour day if the clock records exact horological time—that is, if each swing takes exactly one second to accomplish. Supposing, however, we find that the clock has gained five minutes in this period: this means that the pendulum has oscillated 86,700 times instead of 86,400, or, in other words, each swing has taken a fraction less than a second—to be exact, $8iths of a second—and to adjust the clock the pendulum must be lengthened. If the pendulum length were directly proportional to the time of swing, it would be almost impossible to correct a margin of error such as this; but as the times of vibration are as the square roots of the lengths, a much smaller margin of error than five minutes in the 24-hour day can be corrected by the small turning screw under the pendulum bob.

The next point to be considered is how the effective length of a clock pendulum can be calculated. It is obviously not the total length which is required, as this always remains constant. When we ‘‘shorten” the pendulum, we really screw the disc a trifle nearer to its point of swing. Again, it would be thought that the centre of the arbor, or horizontal rod on which the pendulum crutch swings, would be one point of measurement. This is not so, however, as although the pendulum in its swing carries the crutch with it, the two do not describe exactly the same arc. If the crutch were prolonged, and the bob of the pendulum fixed to the end, at exactly the same level as it usually is on the pendulum itself, the arc of swing would take less time than with the pendulum. Again, if the points of measurement were exactly defined, there would be no need to keep on adjusting the length of the pendulum (variations of temperature not being considered for the moment), as the clockmaker or repairer has to do to ascertain the exact length for the clock to keep accurate time. With a seconds’ dial clock he could measure the pendulum, adjust it exactly to 39.1393 inches in length, and the clock would keep accurate time as a logical necessity. The fact that this length has to be found by experiment is sufficient to show that one at least if not both of the points of measurement cannot be exactly determined.

Let us first consider the disc end of the pendulum. It would be thought at first that the point of measurement here would be the centre of the bob or disc, but this is not the fact. What we have to find is the centre of gravity, ot of the disc, but of the entire pendulum. It is obvious that this central point must be somewhat higher up than the exact centre of the disc. The first point of measurement, therefore, cannot be found by calculation, but only by experiment. To verify this fact: if we add a small weight to the pendulum rod immediately above the disc, we do not shorten the pendulum, but we raise its centre of gravity, and the pendulum will oscillate more quickly and the clock will gain in consequence. If, on the contrary, we add the weight de/ow the disc, the clock will lose.

Let us now turn our attention to the other end of the pendulum, the second point of measurement. Here the pendulum is held from the ‘‘jaws”’ by a flexible piece of steel—the ‘‘suspension,” as it is termed. It is the bending point of this suspension which constitutes the other point of measurement. The steel does not bend at a sharp angle, however, but in a bow, more or less acute according to the size of the arc of swing. It is obvious that there is here no exact point which can be indicated, although such a point does exist. To find this it is necessary to set the clock in motion, measure the length of the pendulum as nearly as possible, and to correct the remaining inaccuracy by the adjusting screw. The length of a clock pendulum, therefore, with a swing of one second, is 39.1393 inches, measured from the centre of gravity of the entire pendulum to the exact bending point of the flexible suspension. This latter can be of steel, or, as is sometimes the case, of string or gut; the problem remains the same.

We know that if we lower the pendulum bob by means of the adjusting screw, the pendulum will take longer to perform its arc of swing. It would be thought, therefore, that if we were to remove the bob altogether, the pendulum would be lengthened to its utmost limit, and the clock would lose the maximum amount in consequence. This is not the case, however, as the following explanation a will show, apart from the question of the alteration of the centre of gravity just referred to. If we suspend a rod, or wire, 39.1393 inches in length from its point of swing to its centre of gravity, and cause it to oscillate in pendulum fashion, it will take approximately one second to swing once through its arc. If to each swing we add an impetus with the finger, we enlarge the arc, but without altering the periodic time. A swing through an arc of one foot and another through six inches will each take one second to accomplish. If, however, we take the wire between the thumb and finger, exerting force in both directions, we can make the pendulum swing through any arc, and in any time we please, according to the degree of force which we exert. In other words, we are using a greater power than the pendulum can control, and the laws governing its swing are temporarily abrogated. This is precisely what occurs when the pendulum disc is removed. The pendulum no longer governs the clock: it is the clock which controls the pendulum ; and the heavier the weight which we put upon the going train, the quicker will the pendulum oscillate. The weight of the pendulum disc, therefore, must be sufficient to overcome the pull of the weight which drives the clock—or the force of the spring, as the case may be—as transmitted from the main to the escape wheels, so that the latter is just enough to maintain the necessary power to prevent the pendulum from ceasing to oscillate.