VI. EPOCH OF THE THEORY OF OXYGEN.--LAVOISIER…

VI. EPOCH OF THE THEORY OF OXYGEN.--LAVOISIER

Sect. 1.--Prelude to the Theory.--Its Publication.

WE arrive now at a great epoch in the history of Chemistry. Few revolutions in science have immediately excited so much general notice as the introduction of the theory of oxygen. The simplicity and symmetry of the modes of combination which it assumed; and, above all, the construction and universal adoption of a nomenclature which applied to all substances, and which seemed to reveal their inmost constitution by their name, naturally gave it an almost irresistible sway over men's minds. We must, however, dispassionately trace the course of its introduction. {276}

Antoine Laurent Lavoisier, an accomplished French chemist, had pursued, with zeal and skill, researches such as those of Black, Cavendish, and Priestley, which we have described above. In 1774, he showed that, in the calcination of metals in air, the metal acquires as much weight as the air loses. It might appear that this discovery at once overturned the view which supposed the metal to be phlogiston added to the calx. Lavoisier's contemporaries were, however, far from allowing this; a greater mass of argument was needed to bring them to this conclusion. Convincing proofs of the new opinion were, however, rapidly supplied. Thus, when Priestley had discovered dephlogisticated air, in 1774, Lavoisier showed, in 1776, that fixed air consisted of charcoal and the dephlogisticated or pure air; for the mercurial calx which, heated by itself, gives out pure air, gives out, when heated with charcoal, fixed air,[27\14] which has, therefore, since been called carbonic acid gas.

[Note 27\14: Mém. Ac. Par. 1775.]

Again, Lavoisier showed that the atmospheric air consists of pure or vital air, and of an unvital air, which he thence called azot. The vital air he found to be the agent in combustion, acidification, calcination, respiration; all of these processes were analogous: all consisted in a decomposition of the atmospheric air, and a fixation of the pure or vital portion of it.

But he thus arrived at the conclusion, that this pure air was added, in all the cases in which, according to the received theory, phlogiston was subtracted, and vice versâ. He gave the name[28\14] of oxygen (principe oxygène) to "the substance which thus unites itself with metals to form their calces, and with combustible substances to form acids."

[Note 28\14: Mém. Ac. Par. 1781, p. 448.]

A new theory was thus produced, which would account for all the facts which the old one would explain, and had besides the evidence of the balance in its favor. But there still remained some apparent objections to be removed. In the action of dilute acids on metals, inflammable air was produced. Whence came this element? The discovery of the decomposition of water sufficiently answered this question, and converted the objection into an argument on the side of the theory: and thus the decomposition of water was, in fact, one of the most critical events for the fortune of the Lavoisierian doctrine, and one which, more than any other, decided chemists in its favor. In succeeding years, Lavoisier showed the consistency of his theory with {277} all that was discovered concerning the composition of alcohol, oil, animal and vegetable substances, and many other bodies.

It is not necessary for us to consider any further the evidence for this theory, but we must record a few circumstances respecting its earlier history. Rey, a French physician, had in 1630, published a book, in which he inquires into the grounds of the increase of the weight of metals by calcination.[29\14] He says, "To this question, then, supported on the grounds already mentioned, I answer, and maintain with confidence, that the increase of weight arises from the air, which is condensed, rendered heavy and adhesive, by the heat of the furnace." Hooke and Mayow had entertained the opinion that the air contains a "nitrous spirit," which is the supporter of combustion. But Lavoisier disclaimed the charge of having derived anything from these sources; nor is it difficult to understand how the received generalizations of the phlogistic theory had thrown all such narrower explanations into obscurity. The merit of Lavoisier consisted in his combining the generality of Stahl with the verified conjectures of Rey and Mayow.

[Note 29\14: Thomson, Hist. Chem. ii. 95.]

No one could have a better claim, by his early enthusiasm for science, his extensive knowledge, and his zealous labors, to hope that a great discovery might fall to his share, than Lavoisier. His father,[30\14] a man of considerable fortune, had allowed him to make science his only profession; and the zealous philosopher collected about him a number of the most active physical inquirers of his time, who met and experimented at his house one day in the week. In this school, the new chemistry was gradually formed. A few years after the publication of Priestley's first experiments, Lavoisier was struck with the presentiment of the theory which he was afterwards to produce. In 1772, he deposited[31\14] with the secretary of the Academy, a note which contained the germ of his future doctrines. "At that time," he says, in explaining this step, "there was a kind of rivalry between France and England in science, which gave importance to new experiments, and which sometimes was the cause that the writers of the one or other of the nations disputed the discovery with the real author." In 1777, the editor of the Memoirs of the Academy speaks of his theory as overturning that of Stahl; but the general acceptance of the new opinion did not take place till later. {278}

[Note 30\14: Biogr. Univ. (Cuvier.)]

[Note 31\14: Thomson, ii. 99.]

Sect. 2.--Reception and Confirmation of the Theory of Oxygen.

THE Oxygen Theory made its way with extraordinary rapidity among the best philosophers.[32\14] In 1785, that is, soon after Cavendish's synthesis of water had removed some of the most formidable objections to it, Berthollet, already an eminent chemist, declared himself a convert. Indeed it was so soon generally adopted in France, that Fourcroy promulgated its doctrines under the name of "La Chimie Française," a title which Lavoisier did not altogether relish. The extraordinary eloquence and success of Fourcroy as a lecturer at the Jardin des Plantes, had no small share in the diffusion of the oxygen theory; and the name of "the apostle of the new chemistry" which was at first given him in ridicule, was justly held by him to be a glorious distinction.[33\14]

[Note 32\14: Thomson, ii. 130.]

[Note 33\14: Cuvier, Eloges, i. p. 20.]

Guyton de Morveau, who had at first been a strenuous advocate of the phlogistic theory, was invited to Paris, and brought over to the opinions of Lavoisier; and soon joined in the formation of the nomenclature founded upon the theory. This step, of which we shall shortly speak, fixed the new doctrine, and diffused it further. Delametherie alone defended the phlogistic theory with vigor, and indeed with violence. He was the editor of the Journal de Physique, and to evade the influence which this gave him, the antiphlogistians[34\14] established, as the vehicle of their opinions, another periodical, the Annales de Chimie.

[Note 34\14: Thomson, ii. 133.]

In England, indeed, their success was not so immediate. Cavendish,[35\14] in his Memoir of 1784, speaks of the question between the two opinions as doubtful. "There are," he says, "several Memoirs of M. Lavoisier, in which he entirely discards phlogiston; and as not only the foregoing experiments, but most other phenomena of nature, seem explicable as well, or nearly as well, upon this as upon the commonly believed principle of phlogiston," Cavendish proceeds to explain his experiments according to the new views, expressing no decided preference, however, for either system. But Kirwan, another English chemist, contested the point much more resolutely. His theory identified inflammable air, or hydrogen, with phlogiston; and in this view, he wrote a work which was intended as a confutation of {279} the essential part of the oxygen theory. It is a strong proof of the steadiness and clearness with which the advocates of the new system possessed their principles, that they immediately translated this work, adding, at the end of each chapter, a refutation of the phlogistic doctrines which it contained. Lavoisier, Berthollet, De Morveau, Fourcroy, and Monge, were the authors of this curious specimen of scientific polemics. It is also remarkable evidence of the candor of Kirwan, that notwithstanding the prominent part he had taken in the controversy, he allowed himself at last to be convinced. After a struggle of ten years, he wrote[36\14] to Berthollet in 1796, "I lay down my arms, and abandon the cause of phlogiston." Black followed the same course. Priestley alone, of all the chemists of great name, would never assent to the new doctrines, though his own discoveries had contributed so much to their establishment. "He saw," says Cuvier,[37\14] "without flinching, the most skilful defenders of the ancient theory go over to the enemy in succession; and when Kirwan had, almost the last of all, abjured phlogiston, Priestley remained alone on the field of battle, and threw out a new challenge, in a memoir addressed to the principal French chemists." It happened, curiously enough, that the challenge was accepted, and the arguments answered by M. Adet, who was at that time (1798,) the French ambassador to the United States, in which country Priestley's work was published. Even in Germany, the birth-place and home of the phlogistic theory, the struggle was not long protracted. There was, indeed, a controversy, the older philosophers being, as usual, the defenders of the established doctrines; but in 1792, Klaproth repeated, before the Academy of Berlin, all the fundamental experiments; and "the result was a full conviction on the part of Klaproth and the Academy, that the Lavoisierian theory was the true one."[38\14] Upon the whole, the introduction of the Lavoisierian theory in the scientific world, when compared with the great revolution of opinion to which it comes nearest in importance, the introduction of the Newtonian theory, shows, by the rapidity and temper with which it took place, a great improvement, both in the means of arriving at truth, and in the spirit with which they were used.

[Note 35\14: Phil. Trans. 1784, p. 150.]

[Note 36\14: Pref. to Fourcroy's Chemistry, xiv.]

[Note 37\14: Cuvier, Eloge de Priestley, p. 208.]

[Note 38\14: Thomson, vol. ii. p. 136.]

Some English writers[39\14] have expressed an opinion that there was {280} little that was original in the new doctrines. But if they were so obvious, what are we to say of eminent chemists, as Black and Cavendish, who hesitated when they were presented, or Kirwan and Priestley, who rejected them? This at least shows that it required some peculiar insight to see the evidence of these truths. To say that most of the materials of Lavoisier's theory existed before him, is only to say that his great merit was, that which must always be the great merit of a new theory, his generalization. The effect which the publication of his doctrines produced, shows us that he was the first person who, possessing clearly the idea of quantitative composition, applied it steadily to a great range of well-ascertained facts. This is, as we have often had to observe, precisely the universal description of an inductive discoverer. It has been objected, in like manner, to the originality of Newton's discoveries, that they were contained in those of Kepler. They were so, but they needed a Newton to find them there. The originality of the theory of oxygen is proved by the conflict, short as it was, which accompanied its promulgation; its importance is shown by the changes which it soon occasioned in every part of the science.

[Note 39\14: Brande, Hist. Diss. in Enc, Brit. p. 182. Lunn, Chem. in Enc. Met. p. 596.]

Thus Lavoisier, far more fortunate than most of those who had, in earlier ages, produced revolutions in science, saw his theory accepted by all the most eminent men of his time, and established over a great part of Europe within a few years from its first promulgation. In the common course of events, it might have been expected that the later years of his life would have been spent amid the admiration and reverence which naturally wait upon the patriarch of a new system of acknowledged truths. But the times in which he lived allowed no such euthanasia to eminence of any kind. The democracy which overthrew the ancient political institutions of France, and swept away the nobles of the land, was not, as might have been expected, enthusiastic in its admiration of a great revolution in science, and forward to offer its homage to the genuine nobility of a great discoverer. Lavoisier was thrown into prison on some wretched charge of having, in the discharge of a public office which he had held, adulterated certain tobacco; but in reality, for the purpose of confiscating his property.[40\14] In his imprisonment, his philosophy was his resource; and he employed himself in the preparation of his papers for printing. When he was brought before the revolutionary tribunal, he begged for a respite of a few days, in order to complete some researches, the results of which {281} were, he said, important to the good of humanity. The brutish idiot, whom the state of the country at that time had placed in the judgment-seat, told him that the republic wanted no sçavans. He was dragged to the guillotine, May the 8th, 1794, and beheaded, in the fifty-second year of his age; a melancholy proof that, in periods of political ferocity, innocence and merit, private virtues and public services, amiable manners and the love of friends, literary fame and exalted genius, are all as nothing to protect their possessor from the last extremes of violence and wrong, inflicted under judicial forms.

[Note 40\14: Biog. Univ. (Cuvier.)]

Sect. 3.--Nomenclature of the Oxygen Theory.

AS we have already said, a powerful instrument in establishing and diffusing the new chemical theory, was a Systematic Nomenclature founded upon it, and applicable to all chemical compounds, which was soon constructed and published by the authors of the theory. Such a nomenclature made its way into general use the more easily, in that the want of such a system had already been severely felt; the names in common use being fantastical, arbitrary, and multiplied beyond measure. The number of known substances had become so great, that a list of names with no regulative principle, founded on accident, caprice, and error, was too cumbrous and inconvenient to be tolerated. Even before the currency which Lavoisier's theory obtained, these evils had led to attempts towards a more convenient set of names. Bergman and Black had constructed such lists; and Guyton de Morveau, a clever and accomplished lawyer of Dijon, had formed a system of nomenclature in 1782, before he had become a convert to Lavoisier's theory, in which task he had been exhorted and encouraged by Bergman and Macquer. In this system,[41\14] we do not find most of the characters of the method which was afterwards adopted. But a few years later, Lavoisier, De Morveau, Berthollet and Fourcroy, associated themselves for the purpose of producing a nomenclature which should correspond to the new theoretical views. This appeared in 1787, and soon made its way into general use. The main features of this system are, a selection of the simplest radical words, by which substances are designated, and a systematic distribution of terminations, to express their relations. Thus, sulphur, combined with oxygen in two different proportions, forms two acids, the {282} sulphur_ous_ and the sulphur_ic_; and these acids form, with earthy or alkaline bases, sulph_ides_ and sulph_ates_; while sulphur directly combined with another element, forms a sulph_uret_. The term oxyd (now usually written oxide) expressed a lower degree of combination with oxygen than the acids. The Méthode de Nomenclature Chimique was published in 1787; and in 1789, Lavoisier published a treatise on chemistry in order further to explain this method. In the preface to this volume, he apologizes for the great amount of the changes, and pleads the authority of Bergman, who had exhorted De Morveau "to spare no improper names; those who are learned will always be learned, and those who are ignorant will thus learn sooner." To this maxim they so far conformed, that their system offers few anomalies; and though the progress of discovery, and the consequent changes of theoretical opinion, which have since gone on, appear now to require a further change of nomenclature, it is no small evidence of the skill with which this scheme was arranged, that for half a century it was universally used, and felt to be far more useful and effective than any nomenclature in any science had ever been before.

[Note 41\14: Journal de Physique, 1782, p. 370.]

VII. APPLICATION AND CORRECTION OF THE OXYGEN THEORY

SINCE a chemical theory, as far as it is true, must enable us to obtain a true view of the intimate composition of all bodies whatever, it will readily be supposed that the new chemistry led to an immense number of analyses and researches of various kinds. These it is not necessary to dwell upon; nor will I even mention the names of any of the intelligent and diligent men who have labored in this field. Perhaps one of the most striking of such analyses was Davy's decomposition of the earths and alkalies into metallic bases and oxygen, in 1807 and 1808; thus extending still further that analogy between the earths and the calces of the metals, which had had so large a share in the formation of chemical theories. This discovery, however, both in the means by which it was made, and in the views to which it led, bears upon subjects hereafter to be treated of.

The Lavoisierian theory also, wide as was the range of truth which it embraced, required some limitation and correction. I do not now {283} speak of some erroneous opinions entertained by the author of the theory; as, for instance, that the heat produced in combustion, and even in respiration, arose from the conversion of oxygen gas to a solid consistence, according to the doctrine of latent heat. Such opinions not being necessarily connected with the general idea of the theory, need not here be considered. But the leading generalization of Lavoisier, that acidification was always combination with oxygen, was found untenable. The point on which the contest on this subject took place was the constitution of the oxymuriatic and muriatic acids;--as they had been termed by Berthollet, from the belief that muriatic acid contained oxygen, and oxymuriatic a still larger dose of oxygen. In opposition to this, a new doctrine was put forward in 1809 by Gay-Lussac and Thenard in France, and by Davy in England;--namely, that oxymuriatic acid was a simple substance, which they termed chlorine, and that muriatic acid was a combination of chlorine with hydrogen, which therefore was called hydrochloric acid. It may be observed, that the point in dispute in the controversy on this subject was nearly the same which had been debated in the course of the establishment of the oxygen theory; namely, whether in the formation of muriatic acid from chlorine, oxygen is subtracted, or hydrogen added, and the water concealed.

In the course of this dispute, it was allowed on both sides, that the combination of dry muriatic acid and ammonia afforded an experimentum crucis; since, if water was produced from these elements, oxygen must have existed in the acid. Davy being at Edinburgh in 1812, this experiment was made in the presence of several eminent philosophers; and the result was found to be, that though a slight dew appeared in the vessel, there was not more than might be ascribed to unavoidable imperfection in the process, and certainly not so much as the old theory of muriatic acid required. The new theory, after this period, obtained a clear superiority in the minds of philosophical chemists, and was further supported by new analogies.[42\14]

[Note 42\14: Paris, Life of Davy, i. 337.]

For, the existence of one hydracid being thus established, it was found that other substances gave similar combinations; and thus chemists obtained the hydriodic, hydrofluoric, and hydrobromic acids. These acids, it is to be observed, form salts with bases, in the same manner as the oxygen acids do. The analogy of the muriatic and fluoric compounds was first clearly urged by a philosopher who was {284} not peculiarly engaged in chemical research, but who was often distinguished by his rapid and happy generalizations, M. Ampère. He supported this analogy by many ingenious and original arguments, in letters written to Davy, while that chemist was engaged in his researches on fluor spar, as Davy himself declares.[43\14]

[Note 43\14: Paris, Life of Davy, i. 370.]

Still further changes have been proposed, in that classification of elementary substances to which the oxygen theory led. It has been held by Berzelius and others, that other elements, as, for example, sulphur, form salts with the alkaline and earthy metals, rather than sulphurets. The character of these sulpho-salts, however, is still questioned among chemists; and therefore it does not become us to speak as if their place in history were settled. Of course, it will easily be understood that, in the same manner in which the oxygen theory introduced its own proper nomenclature, the overthrow or material transformation of the theory would require a change in the nomenclature; or rather, the anomalies which tended to disturb the theory, would, as they were detected, make the theoretical terms be felt as inappropriate, and would suggest the necessity of a reformation in that respect. But the discussion of this point belongs to a step of the science which is to come before us hereafter.

It may be observed, that in approaching the limits of this part of our subject, as we are now doing, the doctrine of the combination of acids and bases, of which we formerly traced the rise and progress, is still assumed as a fundamental relation by which other relations are tested. This remark connects the stage of chemistry now under our notice with its earliest steps. But in order to point out the chemical bearing of the next subjects of our narrative, we may further observe, that metals, earths, salts, are spoken of as known classes of substances; and in like manner the newly-discovered elements, which form the last trophies of chemistry, have been distributed into such classes according to their analogies; thus potassium, sodium, barium, have been asserted to be metals; iodine, bromine, fluorine, have been arranged as analogical to chlorine. Yet there is something vague and indefinite in the boundaries of such classifications and analogies; and it is precisely where this vagueness falls, that the science is still obscure or doubtful. We are led, therefore, to see the dependence of Chemistry upon Classification; and it is to Sciences of Classification which we shall next proceed; as soon as we have noticed the most general views {285} which have been given of chemical relations, namely, the views of the electro-chemists.

But before we do this, we must look back upon a law which obtains in the combination of elements, and which we have hitherto not stated; although it appears, more than any other, to reveal to us the intimate constitution of bodies, and to offer a basis for future generalizations. I speak of the Atomic Theory, as it is usually termed; or, as we might rather call it, the Doctrine of Definite, Reciprocal, and Multiple Proportions.

VIII. THEORY OF DEFINITE, RECIPROCAL, AND MULTIPLE PROPORTIONS

Sect. 1.--Prelude to the Atomic Theory, and its Publication by Dalton.

THE general laws of chemical combination announced by Mr. Dalton are truths of the highest importance in the science, and are now nowhere contested; but the view of matter as constituted of atoms, which he has employed in conveying those laws, and in expressing his opinion of their cause, is neither so important nor so certain. In the place which I here assign to his discovery, as one of the great events of the history of chemistry, I speak only of the law of phenomena, the rules which govern the quantities in which elements combine.

This law may be considered as consisting of three parts, according to the above description of it;--that elements combine in definite proportions;--that these determining proportions operate reciprocally;--and that when, between the same elements, several combining proportions occur, they are related as multiples.

That elements combine in certain definite proportions of quantity, and in no other, was implied, as soon as it was supposed that chemical compounds had any definite properties. Those who first attempted to establish regular formulæ[44\14] for the constitution of salts, minerals, and {286} other compounds, assumed, as the basis of this process, that the elements in different specimens had the same proportion. Wenzel, in 1777, published his Lehre von der Verwandschaft der Körper; or, Doctrine of the Affinities of Bodies; in which he gave many good and accurate analyses. His work, it is said, never grew into general notice. Berthollet, as we have already stated, maintained that chemical compounds were not definite; but this controversy took place at a later period. It ended in the establishment of the doctrine, that there is, for each combination, only one proportion of the elements, or at most only two or three.

[Note 44\14: Thomson, Hist. Chem. vol. ii. p. 279.]

Not only did Wenzel, by his very attempt, presume the first law of chemical composition, the definiteness of the proportions, but he was also led, by his results, to the second rule, that they are reciprocal. For he found that when two neutral salts decompose each other, the resulting salts are also neutral. The neutral character of the salts shows that they are definite compounds; and when the two elements of the one salt, P and s, are presented to those of the other, B and n, if P be in such quantity as to combine definitely with n, B will also combine definitely with s.[45\14]

[Note 45\14: I am told that Wenzel (whose book I have not seen), though he adduces many cases in which double decomposition gives neutral salts, does not express the proposition in a general form, nor use letters in expressing it.]

Views similar to those of Wenzel were also published by Jeremiah Benjamin Richter[46\14] in 1792, in his Anfangsgründe der Stöchyometrie, oder Messkunst Chymischer Elemente, (Principles of the Measure of Chemical Elements) in which he took the law, just stated, of reciprocal proportions, as the basis of his researches, and determined the numerical quantities of the common bases and acids which would saturate each other. It is clear that, by these steps, the two first of our three rules may be considered as fully developed. The change of general views which was at this time going on, probably prevented chemists from feeling so much interest as they might have done otherwise, in these details; the French and English chemists, in particular, were fully employed with their own researches and controversies.

[Note 46\14: Thomson, Hist. Chem. vol. ii. p. 283.]

Thus the rules which had already been published by Wenzel and Richter had attracted so little notice, that we can hardly consider Mr. Dalton as having been anticipated by those writers, when, in 1803, he began to communicate his views on the chemical constitution of {287} bodies; these views being such as to include both these two rules in their most general form, and further, the rule, at that time still more new to chemists, of multiple proportions. He conceived bodies as composed of atoms of their constituent elements, grouped, either one and one, or one and two, or one and three, and so on. Thus, if C represent an atom of carbon and O one of oxygen, O C will be an atom of carbonic oxide, and O C O an atom of carbonic acid; and hence it follows, that while both these bodies have a definite quantity of oxygen to a given quantity of carbon, in the latter substance this quantity is double of what it is in the former.

The consideration of bodies as consisting of compound atoms, each of these being composed of elementary atoms, naturally led to this law of multiple proportions. In this mode of viewing bodies, Mr. Dalton had been preceded (unknown to himself) by Mr. Higgins, who, in 1789, published[47\14] his Comparative View of the Phlogistic and Antiphlogistic Theories. He there says,[48\14] "That in volatile vitriolic acid, a single ultimate particle of sulphur is united only to a single particle of dephlogisticated air; and that in perfect vitriolic acid, every single particle of sulphur is united to two of dephlogisticated air, being the quantity necessary to saturation;" and he reasons in the same manner concerning the constitution of water, and the compounds of nitrogen and oxygen. These observations of Higgins were, however, made casually, and not followed out, and cannot affect Dalton's claim to original merit.

[Note 47\14: Turner's Chem. p. 217.]

[Note 48\14: P. 36 and 37.]

Mr. Dalton's generalization was first suggested[49\14] during his examination of olefiant gas and carburetted hydrogen gas; and was asserted generally, on the strength of a few facts, being, as it were, irresistibly recommended by the clearness and simplicity which the notion possessed. Mr. Dalton himself represented the compound atoms of bodies by symbols, which professed to exhibit the arrangement of the elementary atoms in space as well as their numerical proportion; and he attached great importance to this part of his scheme. It is clear, however, that this part of his doctrine is not essential to that numerical comparison of the law with facts, on which its establishment rests. These hypothetical configurations of atoms have no value till they are confirmed by corresponding facts, such as the optical or crystalline properties of bodies may perhaps one day furnish. {288}

[Note 49\14: Thomson, vol. ii. p. 291.]

Sect. 2.--Reception and Confirmation of the Atomic Theory.

IN order to give a sketch of the progress of the Atomic Theory into general reception, we cannot do better than borrow our information mainly from Dr. Thomson, who was one of the earliest converts and most effective promulgators of the doctrine. Mr. Dalton, at the time when he conceived his theory, was a teacher of mathematics at Manchester, in circumstances which might have been considered narrow, if he himself had been less simple in his manner of life, and less moderate in his worldly views. His experiments were generally made with apparatus of which the simplicity and cheapness corresponded to the rest of his habits. In 1804, he was already in possession of his atomic theory, and explained it to Dr. Thomson, who visited him at that time. It was made known to the chemical world in Dr. Thomson's Chemistry, in 1807; and in Dalton's own System of Chemistry (1808) the leading ideas of it were very briefly stated. Dr. Wollaston's memoir, "on superacid and subacid salts," which appeared in the Philosophical Transactions for 1808, did much to secure this theory a place in the estimation of chemists. Here the author states, that he had observed, in various salts, the quantities of acid combined with the base in the neutral and in the superacid salts to be as one to two: and he says that, thinking it likely this law might obtain generally in such compounds, it was his design to have pursued this subject, with the hope of discovering the cause to which so regular a relation may be ascribed. But he adds, that this appears to be superfluous after the publication of Dalton's theory by Dr. Thomson, since all such facts are but special cases of the general law. We cannot but remark here, that the scrupulous timidity of Wollaston was probably the only impediment to his anticipating Dalton in the publication of the rule of multiple proportions; and the forwardness to generalize, which belongs to the character of the latter, justly secured him, in this instance, the name of the discoverer of this law. The rest of the English chemists soon followed Wollaston and Thomson, though Davy for some time resisted. They objected, indeed, to Dalton's assumption of atoms, and, to avoid this hypothetical step, Wollaston used the phrase chemical equivalents, and Davy the word proportions, for the numbers which expressed Dalton's atomic weights. We may, however, venture to say that the term "atom" is the most convenient, and it need not be understood as claiming our assent to the hypothesis of indivisible molecules. {289}

As Wollaston and Dalton were thus arriving independently at the same result in England, other chemists, in other countries, were, unknown to each other, travelling towards the same point.

In 1807, Berzelius,[50\14] intending to publish a system of chemistry, went through several works little read, and among others the treatises of Richter. He was astonished, he tells us, at the light which was there thrown upon composition and decomposition, and which had never been turned to profit. He was led to a long train of experimental research, and, when he received information of Dalton's ideas concerning multiple proportions, he found, in his own collection of analyses, a full confirmation of this theory.

[Note 50\14: Berz. Chem. B. iii. p. 27.]

Some of the Germans, indeed, appear discontented with the partition of reputation which has taken place with respect to the Theory of Definite Proportions. One[51\14] of them says, "Dalton has only done this;--he has wrapt up the good Richter (whom he knew; compare Schweigger, T, older series, vol. x., p. 381;) in a ragged suit, patched together of atoms; and now poor Richter comes back to his own country in such a garb, like Ulysses, and is not recognized." It is to be recollected, however, that Richter says nothing of multiple proportions.

[Note 51\14: Marx. Gesch. der Cryst. p. 202.]

The general doctrine of the atomic theory is now firmly established over the whole of the chemical world. There remain still several controverted points, as, for instance, whether the atomic weights of all elements are exact multiples of the atomic weight of hydrogen. Dr. Prout advanced several instances in which this appeared to be true, and Dr. Thomson has asserted the law to be of universal application. But, on the other hand, Berzelius and Dr. Turner declare that this hypothesis is at variance with the results of the best analyses. Such controverted points do not belong to our history, which treats only of the progress of scientific truths already recognized by all competent judges.

Though Dalton's discovery was soon generally employed, and universally spoken of with admiration, it did not bring to him anything but barren praise, and he continued in the humble employment of which we have spoken, when his fame had filled Europe, and his name become a household word in the laboratory. After some years he was appointed a corresponding member of the Institute of France; which may be considered as a European recognition of the importance {290} of what he had done; and, in 1826, two medals for the encouragement of science having been placed at the disposal of the Royal Society by the King of England, one of them was assigned to Dalton, "for his development of the atomic theory." In 1833, at the meeting of the British Association for the Advancement of Science, which was held in Cambridge, it was announced that the King had bestowed upon him a pension of 150_l._; at the preceding meeting at Oxford, that university had conferred upon him the degree of Doctor of Laws, a step the more remarkable, since he belonged to the sect of Quakers. At all the meetings of the British Association he has been present, and has always been surrounded by the reverence and admiration of all who feel any sympathy with the progress of science. May he long remain among us thus to remind us of the vast advance which Chemistry owes to him!

[2nd Ed.] [Soon after I wrote these expressions of hope, the period of Dalton's sojourn among us terminated. He died on the 27th of July, 1844, aged 78.

His fellow-townsmen, the inhabitants of Manchester, who had so long taken a pride in his residence among them, soon after his death came to a determination to perpetuate his memory by establishing in his honor a Professor of Chemistry at Manchester.]

Sect. 3.--The Theory of Volumes.--Gay-Lussac.

THE atomic theory, at the very epoch of its introduction into France, received a modification in virtue of a curious discovery then made. Soon after the publication of Dalton's system, Gay-Lussac and Humboldt found a rule for the combination of substances, which includes that of Dalton as far as it goes, but extends to combinations of gases only. This law is the theory of volumes; namely, that gases unite together by volume in very simple and definite proportions. Thus water is composed exactly of 100 measures of oxygen and 200 measures of hydrogen. And since these simple ratios 1 and 1, 1 and 2, 1 and 3, alone prevail in such combinations, it may easily be shown that laws like Dalton's law of multiple proportions, must obtain in such cases as he considered.

[2nd Ed.] [M. Schröder, of Mannheim, has endeavored to extend to solids a law in some degree resembling Gay-Lussac's law of the volumes of gases. According to him, the volumes of the chemical equivalents {291} of simple substances and their compounds are as whole numbers.[52\14] MM. Kopp, Playfair, and Joule have labored in the same field.]

[Note 52\14: Die molecular-volume der Chemischen Verbindungen in festen und flüssingen Zustande, 1843.]

I cannot now attempt to trace other bearings and developments of this remarkable discovery. I hasten on to the last generalization of chemistry; which presents to us chemical forces under a new aspect, and brings us back to the point from which we departed in commencing the history of this science.

IX. EPOCH OF DAVY AND FARADAY

Sect. 1.--Promulgation of the Electro-chemical Theory by Davy.

THE reader will recollect that the History of Chemistry, though highly important and instructive in itself, has been an interruption of the History of Electro-dynamic Research:--a necessary interruption, however; for till we became acquainted with Chemistry in general, we could not follow the course of Electro-chemistry: we could not estimate its vast yet philosophical theories, nor even express its simplest facts. We have now to endeavor to show what has thus been done, and by what steps;--to give a fitting view of the Epoch of Davy and Faraday.

This is, doubtless, a task of difficulty and delicacy. We cannot execute it at all, except we suppose that the great truths, of which the discovery marks this epoch, have already assumed their definite and permanent form. For we do not learn the just value and right place of imperfect attempts and partial advances in science, except by seeing to what they lead. We judge properly of our trials and guesses only when we have gained our point and guessed rightly. We might personify philosophical theories, and might represent them to ourselves as figures, all pressing eagerly onwards in the same {292} direction, whom we have to pursue: and it is only in proportion as we ourselves overtake those figures in the race, and pass beyond them, that we are enabled to look back upon their faces; to discern their real aspects, and to catch the true character of their countenances. Except, therefore, I were of opinion that the great truths which Davy brought into sight have been firmly established and clearly developed by Faraday, I could not pretend to give the history of this striking portion of science. But I trust, by the view I have to offer of these beautiful trains of research and their result, to justify the assumption on which I thus proceed.

I must, however, state, as a further appeal to the reader's indulgence, that, even if the great principles of electro-chemistry have now been brought out in their due form and extent, the discovery is but a very few years, I might rather say a few months, old, and that this novelty adds materially to the difficulty of estimating previous attempts from the point of view to which we are thus led. It is only slowly and by degrees that the mind becomes sufficiently imbued with those new truths, of which the office is, to change the face of a science. We have to consider familiar appearances under a new aspect; to refer old facts to new principles; and it is not till after some time, that the struggle and hesitation which this employment occasions, subsides into a tranquil equilibrium. In the newly acquired provinces of man's intellectual empire, the din and confusion of conquest pass only gradually into quiet and security. We have seen, in the history of all capital discoveries, how hardly they have made their way, even among the most intelligent and candid philosophers of the antecedent schools: we must, therefore, not expect that the metamorphosis of the theoretical views of chemistry which is now going on, will be effected without some trouble and delay.

I shall endeavor to diminish the difficulties of my undertaking, by presenting the earlier investigations in the department of which I have now to speak, as much as possible according to the most deliberate view taken of them by the great discoverers themselves, Davy and Faraday; since these philosophers are they who have taught us the true import of such investigations.

There is a further difficulty in my task, to which I might refer;--the difficulty of speaking, without error and without offence, of men now alive, or who were lately members of social circles which exist still around us. But the scientific history in which such persons play a part, is so important to my purpose, that I do not hesitate to incur {293} the responsibility which the narration involves; and I have endeavored earnestly, and I hope not in vain, to speak as if I were removed by centuries from the personages of my story.

The phenomena observed in the Voltaic apparatus were naturally the subject of many speculations as to their cause, and thus gave rise to "Theories of the Pile." Among these phenomena there was one class which led to most important results: it was discovered by Nicholson and Carlisle, in 1800, that water was decomposed by the pile of Volta; that is, it was found that when the wires of the pile were placed with their ends near each other in the fluid, a stream of bubbles of air arose from each wire, and these airs were found on examination to be oxygen and hydrogen: which, as we have had to narrate, had already been found to be the constituents of water. This was, as Davy says,[53\14] the true origin of all that has been done in electro-chemical science. It was found that other substances also suffered a like decomposition under the same circumstances. Certain metallic solutions were decomposed, and an alkali was separated on the negative plates of the apparatus. Cruickshank, in pursuing these experiments, added to them many important new results; such as the decomposition of muriates of magnesia, soda, and ammonia by the pile; and the general observation that the alkaline matter always appeared at the negative, and the acid at the positive, pole.

[Note 53\14: Phil. Trans. 1826, p. 386.]

Such was the state of the subject when one who was destined to do so much for its advance, first contributed his labors to it. Humphry Davy was a young man who had been apprenticed to a surgeon at Penzance, and having shown an ardent love and a strong aptitude for chemical research, was, in 1798, made the superintendent of a "Pneumatic Institution," established at Bristol by Dr. Beddoes, for the purpose of discovering medical powers of factitious airs.[54\14] But his main attention was soon drawn to galvanism; and when, in consequence of the reputation he had acquired, he was, in 1801, appointed lecturer at the Royal Institution in London (then recently established), he was soon put in possession of a galvanic apparatus of great power; and with this he was not long in obtaining the most striking results.

[Note 54\14: Paris, Life of Davy, i. 58.]

His first paper on the subject[55\14] is sent from Bristol, in September, 1800; and describes experiments, in which he had found that the decompositions observed by Nicholson and Carlisle go on, although the {294} water, or other substance in which the two wires are plunged, be separated into two portions, provided these portions are connected by muscular or other fibres. This use of muscular fibres was, probably, a remnant of the original disposition, or accident, by which galvanism had been connected with physiology, as much as with chemistry. Davy, however, soon went on towards the conclusion, that the phenomena were altogether chemical in their nature. He had already conjectured,[56\14] in 1802, that all decompositions might be polar; that is, that in all cases of chemical decomposition, the elements might be related to each other as electrically positive and negative; a thought which it was the peculiar glory of his school to confirm and place in a distinct light. At this period such a view was far from obvious; and it was contended by many, on the contrary, that the elements which the voltaic apparatus brought to view, were not liberated from combinations, but generated. In 1806, Davy attempted the solution of this question; he showed that the ingredients which had been supposed to be produced by electricity, were due to impurities in the water, or to the decomposition of the vessel; and thus removed all preliminary difficulties. And then he says,[57\14] "referring to my experiments of 1800, 1801, and 1802, and to a number of new facts, which showed that inflammable substances and oxygen, alkalies and acids, and oxidable and noble metals, were in electrical relations of positive and negative, I drew the conclusion, that the combinations and decompositions by electricity were referrible to the law of electrical attractions and repulsions," and advanced the hypothesis, "that chemical and electrical attractions were produced by the same cause, acting in the one case on particles, in the other on masses; . . . and that the same property, under different modifications, was the cause of all the phenomena exhibited by different voltaic combinations."

[Note 55\14: Nicholson's Journal, 4to. iv. 275.]

[Note 56\14: Phil. Trans. 1826.]

[Note 57\14: Ib. 1826, p. 389.]

Although this is the enunciation, in tolerably precise terms, of the great discovery of his epoch, it was, at the period of which we speak, conjectured rather than proved; and we shall find that neither Davy nor his followers, for a considerable period, apprehended it with that distinctness which makes a discovery complete. But in a very short time afterwards, Davy drew great additional notice to his researches by effecting, in pursuance, as it appeared, of his theoretical views, the decomposition of potassa into a metallic base and oxygen. This was, as he truly said, in the memorandum written in his journal at the {295} instant, "a capital experiment." This discovery was soon followed by that of the decomposition of soda; and shortly after, of other bodies of the same kind; and the interest and activity of the whole chemical world were turned to the subject in an intense degree.

At this period, there might be noticed three great branches of speculation on this subject; the theory of the pile, the theory of electrical decomposition, and **the theory of the identity of chemical and electrical forces; which last doctrine, however, was found to include the other two, as might have been anticipated from the time of its first suggestion.

It will not be necessary to say much on the theories of the voltaic pile, as separate from other parts of the subject. The contact-theory, which ascribed the action to the contact of different metals, was maintained by Volta himself; but gradually disappeared, as it was proved (by Wollaston[58\14] especially,) that the effect of the pile was inseparably connected with oxidation or other chemical changes. The theories of electro-chemical decomposition were numerous, and especially after the promulgation of Davy's Memoir in 1806; and, whatever might be the defects under which these speculations for a long time labored, the subject was powerfully urged on in the direction in which truth lay, by Davy's discoveries and views. That there remained something still to be done, in order to give full evidence and consistency to the theory, appears from this;--that some of the most important parts of Davy's results struck his followers as extraordinary paradoxes;--for instance, the fact that the decomposed elements are transferred from one part of the circuit to another, in a form which escapes the cognizance of our senses, through intervening substances for which they have a strong affinity. It was found afterwards that the circumstance which appeared to make the process so wonderful, was, in fact, the condition of its going on at all. Davy's expressions often seem to indicate the most exact notions: for instance, he says, "It is very natural to suppose that the repellent and attractive energies are communicated from one particle to another of the same kind, so as to establish a conducting chain in the fluid; and that the locomotion takes place in consequence;"[59\14] and yet at other times he speaks of the element as attracted and repelled by the metallic surfaces which form the poles;--a different, and, as it appeared afterwards, an untenable view. Mr. Faraday, who supplied what was wanting, justly notices this vagueness. {296} He says,[60\14] that though, in Davy's celebrated Memoir of 1806, the points established are of the utmost value, the mode of action by which the effects take place is stated very generally; so generally, indeed, that probably a dozen precise schemes of electro-chemical action might be drawn up, differing essentially from each other, yet all agreeing with the statement there given." And at a period a little later, being reproached by Davy's brother with injustice in this expression, he substantiated his assertion by an enumeration of twelve such schemes which had been published.

[Note 58\14: Phil. Trans. 1801, p. 427.]

[Note 59\14: Paris, i. 154.]

[Note 60\14: Researches, 482.]

But yet we cannot look upon this Memoir of 1806, otherwise than as a great event, perhaps the most important event of the epoch now under review. And as such it was recognized at once all over Europe. In particular, it received the distinguished honor of being crowned by the Institute of France, although that country and England were then engaged in fierce hostility. Buonaparte had proposed a prize of sixty thousand francs "to the person who by his experiments and discoveries should advance the knowledge of electricity and galvanism, as much as Franklin and Volta did;" and "of three thousand francs for the best experiment which should be made in the course of each year on the galvanic fluid;" the latter prize was, by the First Class of the Institute, awarded to Davy.

From this period he rose rapidly to honors and distinctions, and reached a height of scientific fame as great as has ever fallen to the lot of a discoverer in so short a time. I shall not, however, dwell on such circumstances, but confine myself to the progress of my subject.

Sect. 2.--Establishment of the Electro-chemical Theory by Faraday.

THE defects of Davy's theoretical views will be seen most clearly by explaining what Faraday added to them. Michael Faraday was in every way fitted and led to become Davy's successor in his great career of discovery. In 1812, being then a bookseller's apprentice, he attended the lectures of Davy, which at that period excited the highest admiration.[61\14] "My desire to escape from trade," Mr. Faraday says, "which I thought vicious and selfish, and to enter into the service of science, which I imagined made its pursuers amiable and liberal, induced me at last to take the bold and simple step of writing to Sir H. Davy." He was favorably received, and, in the next year, became {297} Davy's assistant at the Institution; and afterwards his successor. The Institution which produced such researches as those of these two men, may well be considered as a great school of exact and philosophical chemistry. Mr. Faraday, from the beginning of his course of inquiry, appears to have had the consciousness that he was engaged on a great connected work. His Experimental Researches, which appeared in a series of Memoirs in the Philosophical Transactions, are divided into short paragraphs, numbered into a continued order from 1 up to 1160, at the time at which I write;[62\14] and destined, probably, to extend much further. These paragraphs are connected by a very rigorous method of investigation and reasoning which runs through the whole body of them. Yet this unity of purpose was not at first obvious. His first two Memoirs were upon subjects which we have already treated of (B. xiii. c. 5 and c. 8), Voltaic Induction, and the evolution of Electricity from Magnetism. His "Third Series" has also been already referred to. Its object was, as a preparatory step towards further investigation, to show the identity of voltaic and animal electricity with that of the electrical machine; and as machine electricity differs from other kinds in being successively in a state of tension and explosion, instead of a continued current, Mr. Faraday succeeded in identifying it with them, by causing the electrical discharge to pass through a bad conductor into a discharging-train of vast extent; nothing less, indeed, than the whole fabric of the metallic gas-pipes and water-pipes of London. In this Memoir[63\14] it is easy to see already traces of the general theoretical views at which he had arrived; but these are not expressly stated till his "Fifth Series;" his intermediate Fourth Series being occupied by another subsidiary labor on the conditions of conduction. At length, however, in the Fifth Series, which was read to the Royal Society in June, 1833, he approaches the theory of electro-chemical decomposition. Most preceding theorists, and Davy amongst the number, had referred this result to attractive powers residing in the poles of the apparatus; and had even pretended to compare the intensity of this attraction at different distances from the poles. By a number of singularly beautiful and skilful experiments, Mr. Faraday shows that the phenomena can with no propriety be {298} ascribed to the attraction of the poles.[64\14] "As the substances evolved in cases of electro-chemical decomposition may be made to appear against air,[65\14] which, according to common language, is not a conductor, nor is decomposed; or against water,[66\14] which is a conductor, and can be decomposed; as well as against the metal poles, which are excellent conductors, but undecomposable; there appears but little reason to consider this phenomenon generally as due to the attraction or attractive powers of the latter, when used in the ordinary way, since similar attractions can hardly be imagined in the former instances."

[Note 61\14: Paris, ii. 3.]

[Note 62\14: December, 1835. (At present, when I am revising the second edition, September, 1846, Dr. Faraday has recently published the "Twenty-first Series" of his Researches ending with paragraph 2453.)]

[Note 63\14: Phil. Trans. 1833.]

[Note 64\14: Researches, Art. 497]

[Note 65\14: Researches, Arts. 465, 469.]

[Note 66\14: 495.]

Faraday's opinion, and, indeed, the only way of expressing the results of his experiments, was, that the chemical elements, in obedience to the direction of the voltaic currents established in the decomposing substance, were evolved, or, as he prefers to say, ejected at its extremities.[67\14] He afterwards states that the influence which is present in the electric current may be described[68\14] as an axis of power, having [at each point] contrary forces exactly equal in amount in contrary directions.

[Note 67\14: 493.]

[Note 68\14: 517.]

Having arrived at this point, Faraday rightly wished to reject the term poles, and other words which could hardly be used without suggesting doctrines now proved to be erroneous. He considered, in the case of bodies electrically decomposed, or, as he termed them, electrolytes, the elements as travelling in two opposite directions; which, with reference to the direction of terrestrial magnetism, might be considered as naturally east and west; and he conceived elements as, in this way, arriving at the doors or outlets at which they finally made their separate appearance. The doors he called electrodes, and, separately, the anode and the cathode;[69\14] and the elements which thus travel he termed the anïon and the catïon (or cathïon).[70\14] By means of this nomenclature he was able to express his general results with much more distinctness and facility.

[Note 69\14: 663.]

[Note 70\14: The analogy of the Greek derivation requires catïon; but to make the relation to cathode obvious to the English reader, and to avoid a violation of the habits of English pronunciation, I should prefer cathïon.]

But this general view of the electrolytical process required to be pursued further, in order to explain the nature of the action. The identity of electrical and chemical forces, which had been hazarded as {299} a conjecture by Davy, and adopted as the basis of chemistry by Berzelius, could only be established by exact measures and rigorous proofs. Faraday had, in his proof of the identity of voltaic and electric agency, attempted also to devise such a measure as should give him a comparison of their quantity; and in this way he proved that[71\14] a voltaic group of two small wires of platinum and zinc, placed near each other, and immersed in dilute acid for three seconds, yields as much electricity as the electrical battery, charged by ten turns of a large machine; and this was established both by its momentary electro-magnetic effect, and by the amount of its chemical action.[72\14]

[Note 71\14: Researches, Art. 371.]

[Note 72\14: 537.]

It was in his "Seventh Series," that he finally established a principle of definite measurement of the amount of electrolytical action, and described an instrument which he termed[73\14] a volta-electrometer. In this instrument the amount of action was measured by the quantity of water decomposed: and it was necessary, in order to give validity to the mensuration, to show (as Faraday did show) that neither the size of the electrodes, nor the intensity of the current, nor the strength of the acid solution which acted on the plates of the pile, disturbed the accuracy of this measure. He proved, by experiments upon a great variety of substances, of the most different kinds, that the electro-chemical action is definite in amount according to the measurement of the new instrument.[74\14] He had already, at an earlier period,[75\14] asserted, that the chemical power of a current of electricity is in direct proportion to the absolute quantity of electricity which passes; but the volta-electrometer enabled him to fix with more precision the meaning of this general proposition, as well as to place it beyond doubt.

[Note 73\14: 739.]

[Note 74\14: Arts. 758, 814.]

[Note 75\14: 377.]

The vast importance of this step in chemistry soon came into view. By the use of the volta-electrometer, Faraday obtained, for each elementary substance, a number which represented the relative amount of its decomposition, and which might properly[76\14] be called its "electro-chemical equivalent." And the question naturally occurs, whether these numbers bore any relation to any previously established chemical measures. The answer is remarkable. They were no other than the atomic weights of the Daltonian theory, which formed the climax of the previous ascent of chemistry; and thus here, as everywhere in {300} the progress of science, the generalizations of one generation are absorbed in the wider generalizations of the next.

[Note 76\14: 792.]

But in order to reach securely this wider generalization, Faraday combined the two branches of the subject which we have already noticed;--the theory of electrical decomposition with the theory of the pile. For his researches on the origin of activity of the voltaic circuit (his Eighth Series), led him to see more clearly than any one before him, what, as we have said, the most sagacious of preceding philosophers had maintained, that the current in the pile was due to the mutual chemical action of its elements. He was led to consider the processes which go on in the exciting-cell and in the decomposing place as of the same kind, but opposite in direction. The chemical composition of the fluid with the zinc, in the common apparatus, produces, when the circuit is completed, a current of electric influence in the wire; and this current, if it pass through an electrolyte, manifests itself by decomposition, overcoming the chemical affinity which there resists it. An electrolyte cannot conduct without being decomposed. The forces at the point of composition and the point of decomposition are of the same kind, and are opposed to each other by means of the conducting-wire; the wire may properly be spoken of[77\14] as conducting chemical affinity: it allows two forces of the same kind to oppose one another;[78\14] electricity is only another mode of the exertion of chemical forces;[79\14] and we might express all the circumstances of the voltaic pile without using any other term than chemical affinity, though that of electricity may be very convenient.[80\14] Bodies are held together by a definite power, which, when it ceases to discharge that office, may be thrown into the condition of an electric current.[81\14]

[Note 77\14: Researches Art. 918.]

[Note 78\14: 910.]

[Note 79\14: 915.]

[Note 80\14: 917.]

[Note 81\14: 855.]

Thus the great principle of the identity of electrical and chemical action was completely established. It was, as Faraday with great candor says,[82\14] a confirmation of the general views put forth by Davy, in 1806, and might be expressed in his terms, that "chemical and electrical attractions are produced by the same cause;" but it is easy to see that neither was the full import of these expressions understood nor were the quantities to which they refer conceived as measurable quantities, nor was the assertion anything but a sagacious conjecture, till Faraday gave the interpretation, measure, and proof, of which we have spoken. The evidence of the incompleteness of the views of his predecessor we have already adduced, in speaking of his vague and {301} inconsistent theoretical account of decomposition. The confirmation of Davy's discoveries by Faraday is of the nature of Newton's confirmation of the views of Borelli and Hooke respecting gravity, or like Young's confirmation of the undulatory theory of Huyghens.

[Note 82\14: 965.]

We must not omit to repeat here the moral which we wish to draw from all great discoveries, that they depend upon the combination of exact facts with clear ideas. The former of these conditions is easily illustrated in the case of Davy and Faraday, both admirable and delicate experimenters. Davy's rapidity and resource in experimenting were extraordinary,[83\14] and extreme elegance and ingenuity distinguish almost every process of Faraday. He had published, in 1829, a work on Chemical Manipulation, in which directions are given for performing in the neatest manner all chemical processes. Manipulation, as he there truly says, is to the chemist like the external senses to the mind;[84\14] and without the supply of fit materials which such senses only can give, the mind can acquire no real knowledge.

[Note 83\14: Paris, i. 145.]

[Note 84\14: Pref. p. ii.]

But still the operations of the mind as well as the information of the senses, ideas as well as facts, are requisite for the attainment of any knowledge; and all great steps in science require a peculiar distinctness and vividness of thought in the discoverer. This it is difficult to exemplify in any better way than by the discoveries themselves. Both Davy and Faraday possessed this vividness of mind; and it was a consequence of this endowment, that Davy's **lectures upon chemistry, and Faraday's upon almost any subject of physical philosophy, were of the most brilliant and captivating character. In discovering the nature of voltaic action, the essential intellectual requisite was to have a distinct conception of that which Faraday expressed by the remarkable phrase,[85\14] "an axis of power having equal and opposite forces;" and the distinctness of this idea in Faraday's mind shines forth in every part of his writings. Thus he says, the force which determines the decomposition of a body is in the body, not in the poles.[86\14] But for the most part he can of course only convey this fundamental idea by illustrations. Thus[87\14] he represents the voltaic circuit by a double circle, studded with the elements of the circuit, and shows how the anïons travel round it in one direction, and the cathïons in the opposite. He considers[88\14] the powers at the two places of action as balancing against each other through the medium of the conductors, in a manner {302} analogous to that in which mechanical forces are balanced against each other by the intervention of the lever. It is impossible to him[89\14] to resist the idea, that the voltaic current must be preceded by a state of tension in its interrupted condition, which is relieved when the circuit is completed. He appears to possess the idea of this kind of force with the same eminent distinctness with which Archimedes in the ancient, and Stevinus in the modern history of science, possessed the idea of pressure, and were thus able to found the science of mechanics.[90\14] And when he cannot obtain these distinct modes of conception, he is dissatisfied, and conscious of defect. Thus in the relation between magnetism and electricity,[91\14] "there appears to be a link in the chain of effects, a wheel in the physical mechanism of the action, as yet unrecognized." All this variety of expression shows how deeply seated is the thought. This conception of Chemical Affinity as a peculiar influence of force, which, acting in opposite directions, combines and resolves bodies;--which may be liberated and thrown into the form of a voltaic current, and thus be transferred to remote points, and applied in various ways; is essential to the understanding, as it was to the making, of these discoveries.

[Note 85\14: Art. 517.]

[Note 86\14: Art. 661.]

[Note 87\14: **963.]

[Note 88\14: 917.]

[Note 89\14: Art. 950.]

[Note 90\14: 990.]

[Note 91\14: 1114.]

By those to whom this conception has been conveyed, I venture to trust that I shall be held to have given a faithful account of this important event in the history of science. We may, before we quit the subject, notice one or two of the remarkable subordinate features of Faraday's discoveries.

Sect. 3.--Consequences of Faraday's Discoveries.

FARADAY'S volta-electrometer, in conjunction with the method he had already employed, as we have seen, for the comparison of voltaic and common electricity, enabled him to measure the actual quantity of electricity which is exhibited, in given cases, in the form of chemical affinity. His results appeared in numbers of that enormous amount which so often comes before us in the expression of natural laws. One grain of water[92\14] will require for its decomposition as much electricity as would make a powerful flash of lightning. By further calculation, he finds this quantity to be not less than 800,000 charges of his Leyden battery;[93\14] and this is, by his theory of the identity of the combining with the decomposing force, the quantity of electricity {303} which is naturally associated with the elements of the grain of water, endowing them with their mutual affinity.

[Note 92\14: **853.]

[Note 93\14: 861.]

Many of the subordinate facts and laws which were brought to light by these researches, clearly point to generalizations, not included in that which we have had to consider, and not yet discovered: such laws do not properly belong to our main plan, which is to make our way up to the generalizations. But there is one which so evidently promises to have an important bearing on future chemical theories, that I will briefly mention it. The class of bodies which are capable of electrical decomposition is limited by a very remarkable law: they are such binary compounds only as consist of single proportionals of their elementary principles. It does not belong to us here to speculate on the possible import of this curious law; which, if not fully established, Faraday has rendered, at least, highly probable:[94\14] but it is impossible not to see how closely it connects the Atomic with the Electro-chemical Theory; and in the connexion of these two great members of Chemistry, is involved the prospect of its reaching wider generalizations, and principles more profound than we have yet caught sight of.

[Note 94\14: Art. 697.]

As another example of this connexion, I will, finally, notice that Faraday has employed his discoveries in order to decide, in some doubtful cases, what is the true chemical equivalent;[95\14] "I have such conviction," he says, "that the power which governs electro-decomposition and ordinary chemical attractions is the same; and such confidence in the overruling influence of those natural laws which render the former definite, as to feel no hesitation in believing that the latter must submit to them too. Such being the case, I can have no doubt that, assuming hydrogen as 1, and dismissing small fractions for the simplicity of expression, the equivalent number or atomic weight of oxygen is 8, of chlorine 36, of bromine 78·4, of lead 103·5, of tin 59, &c.; notwithstanding that a very high authority doubles several of these numbers."

[Note 95\14: 851.]

Sect. 4.--Reception of the Electro-chemical Theory.

THE epoch of establishment of the electro-chemical theory, like other great scientific epochs, must have its sequel, the period of its reception and confirmation, application and extension. In that period we {304} are living, and it must be the task of future historians to trace its course.

We may, however, say a word on the reception which the theory met with, in the forms which it assumed, anterior to the labors of Faraday. Even before the great discovery of Davy, Grotthuss, in 1805, had written upon the theory of electro-chemical decomposition; but he and, as we have seen, Davy, and afterwards other writers, as Riffault and Chompré, in 1807, referred the effects to the poles.[96\14] But the most important attempt to appropriate and employ the generalization which these discoveries suggested, was that of Berzelius; who adopted at once the view of the identity, or at least the universal connexion, of electrical relations with chemical affinity. He considered,[97\14] that in all chemical combinations the elements may be considered as electro-positive and electro-negative; and made this opposition the basis of his chemical doctrines; in which he was followed by a large body of the chemists of Germany. He held too that the heat and light, evolved during cases of powerful combination, are the consequence of the electric discharge which is at that moment taking place: a conjecture which Faraday at first spoke of with praise.[98\14] But at a later period he more sagely says,[99\14] that the flame which is produced in such cases exhibits but a small portion of the electric power which really acts. "These therefore may not, cannot, be taken as evidences of the nature of the action; but are merely incidental results, incomparably small in relation to the forces concerned, and supplying no information of the way in which the particles are active on each other, or in which their forces are finally arranged." And comparing the evidence which he himself had given of the principle on which Berzelius's speculations rested, with the speculations themselves, Faraday justly conceived, that he had transferred the doctrine from the domain of what he calls doubtful knowledge, to that of inductive certainty.

[Note 96\14: Faraday (Researches, Art. 481, 492).]

[Note 97\14: Ann. Chim. lxxxvi. 146, for 1813.]

[Note 98\14: Researches, Art. 870]

[Note 99\14: 960.]

Now that we are arrived at the starting-place, from which this well-proved truth, the identity of electric and chemical forces, must make its future advances, it would be trifling to dwell longer on the details of the diffusion of that doubtful knowledge which preceded this more certain science. Our history of chemistry is, therefore, here at an end. I have, as far as I could, executed my task; which was, to mark all the {305} great steps of its advance, from the most unconnected facts and the most imperfect speculations, to the highest generalization at which chemical philosophers have yet arrived.

Yet it will appear to our purpose to say a few words on the connexion of this science with those of which we are next to treat; and that I now proceed to do.

X. TRANSITION FROM THE CHEMICAL TO THE CLASSIFICATORY SCIENCES

IT is the object and the boast of chemistry to acquire a knowledge of bodies which is more exact and constant than any knowledge borrowed from their sensible qualities can be; since it penetrates into their intimate constitution, and discloses to us the invariable laws of their composition. But yet it will be seen, on a little reflection, that such knowledge could not have any existence, if we were not also attentive to their sensible qualities.

The whole fabric of chemistry rests, even at the present day, upon the opposition of acids and bases: an acid was certainly at first known by its sensible qualities, and how otherwise, even now, do we perceive its quality? It was a great discovery of modern times that earths and alkalies have for their bases metals: but what are metals? or how, except from lustre, hardness, weight, and the like, do we recognize a body as a metal? And how, except by such characters, even before its analysis, was it known to be an earth or an alkali? We must suppose some classification established, before we can make any advance by experiment or observation.

It is easy to see that all attempts to avoid this difficulty by referring to processes and analogies, as well as to substances, bring us back to the same point in a circle of fallacies. If we say that an acid and alkali are known by combining with each other, we still must ask, What is the criterion that they have combined? If we say that the distinctive qualities of metals and earths are, that metals become earths by oxidation, we must still inquire how we recognize the process of oxidation? We have seen how important a part combustion plays in the history of chemical speculation; and we may usefully form such classes of {306} bodies as combustibles and supporters of combustion. But even combustion is not capable of being infallibly known, for it passes by insensible shades into oxidation. We can find no basis for our reasonings, which does not assume a classification of obvious facts and qualities.

But any classification of substances on such grounds, appears, at first sight, to involve us in vagueness, ambiguity, and contradiction. Do we really take the sensible qualities of an acid as the criterion of its being an acid?--for instance, its sourness? Prussic acid, arsenious acid, are not sour. "I remember," says Dr. Paris,[100\14] "a chemist having been exposed to much ridicule from speaking of a sweet acid,--why not?" When Davy had discovered potassium, it was disputed whether it was a metal; for though its lustre and texture are metallic, it is so light as to swim on water. And if potassium be allowed to be a metal, is silicium one, a body which wants the metallic lustre, and is a non-conductor of electricity? It is clear that, at least, the obvious application of a classification by physical characters, is attended with endless perplexity.

[Note 100\14: Life of Davy, i. 263.]

But since we cannot even begin our researches without assuming a classification, and since the forms of such a classification which first occur, end in apparent confusion, it is clear that we must look to our philosophy for a solution of this difficulty; and must avoid the embarrassments and contradictions of casual and unreflective classification, by obtaining a consistent and philosophical arrangement. We must employ external characters and analogies in a connected and systematic manner; we must have Classificatory Sciences, and these must have a bearing even on Chemistry.

Accordingly, the most philosophical chemists now proceed upon this principle. "The method which I have followed," says M. Thenard, in his Traité de Chimie, published in 1824, "is, to unite in one group all analogous bodies; and the advantage of this method, which is that employed by naturalists, is very great, especially in the study of the metals and their compounds."[101\14] In this, as in all good systems of chemistry, which have appeared since the establishment of the phlogistic theory, combustion, and the analogous processes, are one great element in the arrangement, while the difference of metallic and non-metallic, is another element. Thus Thenard, in the first place, speaks of Oxygen; in the next place, of the Non-metallic Combustibles, as Hydrogen, Carbon, Sulphur, Chlorine; and in the next place, of Metals. But the Metals are again divided into six Sections, with reference, {307} principally, to their facility of combination with oxygen. Thus, the First Section is the Metals of the Earths; the Second, the Metals of the Alkalies; the Third, the Easily Oxidable Metals, as Iron; the Fourth, Metals Less Oxidable, as Copper and Lead; the Fifth Section contains only Mercury and Osmium; and the Sixth, what were at an earlier period termed the Noble Metals, Gold, Silver, Platinum, and others.

[Note 101\14: Pref., p. viii.]

How such principles are to be applied, so as to produce a definite and consistent arrangement, will be explained in speaking of the philosophy of the Classificatory Sciences; but there are one or two peculiarities in the classes of bodies thus recognized by modern chemistry, which it may be useful to notice.

1. The distinction of Metallic and Non-metallic is still employed, as of fundamental importance. The discovery of new metals is so much connected with the inquiries concerning chemical elements, that we may notice the general progress of such discoveries. Gold, Silver, Iron, Copper, Quicksilver, Lead, Tin, were known from the earliest antiquity. In the beginning of the sixteenth century, mine-directors, like George Agricola, had advanced so far in practical metallurgy, that they had discovered the means of extracting three additional metals, Zinc, Bismuth, Antimony. After this, there was no new metal discovered for a century, and then such discoveries were made by the theoretical chemists, a race of men who had not existed before Beccher and Stahl. Thus Arsenic and Cobalt were made known by Brandt, in the middle of the eighteenth century, and we have a long list of similar discoveries belonging to the same period; Nickel, Manganese, and Tungsten, which were detected by Cronstedt, Gahn, and Scheele, and Delhuyart, respectively; metals of a very different kind, Tellurium and Molybdenum, which were brought to light by Müller, Scheele, Bergman, and Hielm; Platinum, which was known as early as 1741, but with the ore of which, in 1802 and 1803, the English chemists, Wollaston and Tennant, found that no less than four other new metals (Palladium, Rhodium, Iridium and Osmium) were associated. Finally, (omitting some other new metals,) we have another period of discovery, opened in 1807, by Davy's discovery of Potassium, and including the resolution of all, or almost all, the alkalies and earths into metallic bases.

[2nd Ed.] [The next few years made some, at least some conjectural, additions to the list of simple substances, detected by a more minute scrutiny of known substances. Thorium was discovered by Berzelius in 1828; and Vanadium by Professor Sefström in 1830. A {308} metal named Cerium, was discovered in 1803, by Hisinger and Berzelius, in a rare Swedish mineral known by the name of Cerit. Mosander more recently has found combined with Cerium, other new metals which he has called Lanthanium, Didymium, Erbium, and Terbium: M. Klaus has found a new metal, Ruthenium, in the ore of Platinum; and Rose has discovered in Tantalite two other new metals, which he has announced under the names of Pelopium and Niobium. Svanberg is said to have discovered a new earth in Eudialyt, which is supposed to have, like the rest, a new radical. If these last discoveries be confirmed, the number of simple substances will be raised to sixty-two.]

2. Attempts have been made to indicate the classification of chemical substances by some peculiarity in the Name; and the Metals, for example, have been designated generally by names in um, like the Latin names of the ancient metals, aurum, ferrum. This artifice is a convenient nomenclature for the purpose of marking a recognized difference; and it would be worth the while of chemists to agree to make it universal, by writing molybden_um_ and platin_um_; which is sometimes done, but not always.

3. I am not now to attempt to determine how far this class,--Metals,--extends; but where the analogies of the class cease to hold there the nomenclature must also change. Thus, some chemists, as Dr. Thomson, have conceived that the base of Silica is more analogous to Carbon and Boron, which form acids with oxygen, than it is to the metals: and he has accordingly associated this base with these substances, and has given it the same termination, Silicon. But on the validity of this analogy chemists appear not to be generally agreed.

4. There is another class of bodies which have attracted much notice among modern chemists, and which have also been assimilated to each other in the form of their names; the English writers calling them Chlorine, Fluorine, Iodine, Bromine, while the French use the terms Chlore, Phtore, Iode, Brome. We have already noticed the establishment of the doctrine--that muriatic acid is formed of a base, chlorine, and of hydrogen,--as a great reform in the oxygen theory; with regard to which rival claims were advanced by Davy, and by MM. Gay-Lussac and Thenard in 1800. Iodine, a remarkable body which, from a dark powder, is converted into a violet-colored gas by the application of heat, was also, in 1813, the subject of a similar rivalry between the same English and French chemists. Bromine {309} was only discovered as late as 1826; and Fluorine, or Phtore, as, from its destructive nature, it has been proposed to term it, has not been obtained as a separate substance, and is inferred to exist by analogy only. The analogies of these bodies (Chlore, Phtore, &c.) are very peculiar; for instance, by combination with metals they form salts; by combination with hydrogen they form very strong acids; and all, at the common temperature of the atmosphere, operate on other bodies in the most energetic manner. Berzelius[102\14] proposes to call them halogenous bodies, or halogenes.

[Note 102\14: Chem. i. 262.]

5. The number of Elementary Substances which are at present presented in our treatises of chemistry[103\14] is fifty-three, [or rather, as we have said above, sixty-two.] It is naturally often asked what evidence we have, that all these are elementary, and what evidence that they are all the elementary bodies;--how we know that new elements may not hereafter be discovered, or these supposed simple bodies resolved into simpler still? To these questions we can only answer, by referring to the history of chemistry;--by pointing out what chemists have understood by analysis, according to the preceding narrative. They have considered, as the analysis of a substance, that elementary constitution of it which gives the only intelligible explanation of the results of chemical manipulation, and which is proved to be complete as to quantity, by the balance, since the whole can only be equal to all its parts. It is impossible to maintain that new substances may not hereafter be discovered; for they may lurk, even in familiar substances, in doses so minute that they have not yet been missed amid the inevitable slight inaccuracies of all analysis; in the way in which iodine and bromine remained so long undetected in sea-water; and new minerals, or old ones not yet sufficiently examined, can hardly fail to add something to our list. As to the possibility of a further analysis of our supposed simple bodies, we may venture to say that, in regard to such supposed simple bodies as compose a numerous and well-characterized class, no such step can be made, except through some great change in chemical theory, which gives us a new view of all the general relations which chemistry has yet discovered. The proper evidence of the reality of any supposed new analysis is, that it is more consistent with the known analogies of chemistry, to suppose the process analytical than synthetical. Thus, as has already been said, chemists admit the existence of fluorine, from the analogy of chlorine; and Davy, when it was found {310} that ammonia formed an amalgam with mercury, was tempted to assign to it a metallic basis. But then he again hesitates,[104\14] and doubts whether the analogies of our knowledge are not better preserved by supposing that ammonia, as a compound of hydrogen and another principle, is "a type of the composition of the metals."

[Note 103\14: Turner, p. 971.]

[Note 104\14: Elem. Chem. Phil. 1812, p. 481.]

Our history, which is the history of what we know, has little to do with such conjectures. There are, however, some not unimportant principles which bear upon them, and which, as they are usually employed, belong to the science which next comes under our review, Mineralogy.

{{311}} BOOK XV.

THE ANALYTICO-CLASSIFICATORY SCIENCE.

HISTORY OF MINERALOGY.

Κρύσταλλον φαέθοντα διαυγέα λάζεο χερσὶ, Λᾶαν ἀπόῤῥοιαν περιφεγγέος ἀμβρότου αἴγλης, Αἰθέρι δ' ἀθανάτων μέγα τέρπεται ἄφθιτον ἦτορ. Τόν κ' εἴπερ μετὰ χειρὰς ἔχων, περὶ νηὸν ἵκηαι, Οὔτις τοι μακάρων ἀρνήσεται εὐχωλῆσι. ORPHEUS. Lithica.

Now, if the bold but pious thought be thine, To reach our spacious temple's inner shrine, Take in thy reverent hands the crystal stone, Where heavenly light in earthy shroud is shown:-- Where, moulded into measured form, with rays Complex yet clear, the eternal Ether plays; This if thou firmly hold and rightly use, Not long the gods thy ardent wish refuse.

{{313}} INTRODUCTION.

Sect. 1.--Of the Classificatory Sciences.

THE horizon of the sciences spreads wider and wider before us, as we advance in our task of taking a survey of the vast domain. We have seen that the existence of Chemistry as a science which declares the ingredients and essential constitution of all kinds of bodies, implies the existence of another corresponding science, which shall divide bodies into kinds, and point out steadily and precisely what bodies they are which we have analysed. But a science thus dividing and defining bodies, is but one member of an order of sciences, different from those which we have hitherto described; namely, of the classificatory sciences. Such sciences there must be, not only having reference to the bodies with which chemistry deals, but also to all things respecting which we aspire to obtain any general knowledge, as, for instance, plants and animals. Indeed it will be found, that it is with regard to these latter objects, to organized beings, that the process of scientific classification has been most successfully exercised; while with regard to inorganic substances, the formation of a satisfactory system of arrangement has been found extremely difficult; nor has the necessity of such a system been recognised by chemists so distinctly and constantly as it ought to be. The best exemplification of these branches of knowledge, of which we now have to speak, will, therefore, be found in the organic world, in Botany and Zoology; but we will, in the first place, take a brief view of the science which classifies inorganic bodies, and of which Mineralogy is hitherto the very imperfect representative.

The principles and rules of the Classificatory Sciences, as well as of those of the other orders of sciences, must be fully explained when we come to treat of the Philosophy of the Sciences; and cannot be introduced here, where we have to do with history only. But I may observe very briefly, that with the process of classing, is joined the process of naming;--that names imply classification;--and that even the rudest and earliest application of language presupposes a distribution of objects according to their kinds;--but that such a spontaneous {314} and unsystematic distribution cannot, in the cases we now have to consider, answer the purposes of exact and general knowledge. Our classification of objects must be made consistent and systematic, in order to be scientific; we must discover marks and characters, properties and conditions, which are constant in their occurrence and relations; we must form our classes, we must impose our names, according to such marks. We can thus, and thus alone, arrive at that precise, certain, and systematic knowledge, which we seek; that is, at science. The object, then, of the classificatory sciences is to obtain FIXED CHARACTERS of the kinds of things; and the criterion of the fitness of names is, that THEY MAKE GENERAL PROPOSITIONS POSSIBLE.

I proceed to review the progress of certain sciences on these principles, and first, though briefly, the science of Mineralogy.

Sect. 2.--Mineralogy as the Analytico-classificatory Science.

MINERALOGY, as it has hitherto been cultivated, is, as I have already said, an imperfect representative of the department of human knowledge to which it belongs. The attempts at the science have generally been made by collecting various kinds of information respecting mineral bodies; but the science which we require is a complete and consistent classified system of all inorganic bodies. For chemistry proceeds upon the principle that the constitution of a body invariably determines its properties; and, consequently, its kind: but we cannot apply this principle, except we can speak with precision of the kind of a body, as well as of its composition. We cannot attach any sense to the assertion, that "soda or baryta has a metal for its base," except we know what a metal is, or at least what properties it implies. It may not be, indeed it is not, possible, to define the kinds of bodies by words only; but the classification must proceed by some constant and generally applicable process; and the knowledge which has reference to the classification will be precise as far as this process is precise, and vague as far as this is vague.

There must be, then, as a necessary supplement to Chemistry, a Science of those properties of bodies by which we divide them into kinds. Mineralogy is the branch of knowledge which has discharged the office of such a science, so far as it has been discharged; and, indeed, Mineralogy has been gradually approaching to a clear consciousness of her real place, and of her whole task; I shall give the history of some of the advances which have thus been made. They are, principally, {315} the establishment and use of External Characters, especially of Crystalline Form, as a fixed character of definite substances; and the attempts to bring into view the connexion of Chemical Constitution and External Properties, made in the shape of mineralogical Systems; both those in which chemical methods of arrangement are adopted, and those which profess to classify by the natural-history method.

{{316}} CRYSTALLOGRAPHY.

I. PRELUDE TO THE EPOCH OF DE LISLE AND HAÜY

OF all the physical properties of bodies, there is none so fixed, and in every way so remarkable, as this;--that the same chemical compound always assumes, with the utmost precision, the same geometrical form. This identity, however, is not immediately obvious; it is often obscured by various mixtures and imperfections in the substance; and even when it is complete, it is not immediately recognized by a common eye, since it consists, not in the equality of the sides or faces of the figures, but in the equality of their angles. Hence it is not surprising that the constancy of form was not detected by the early observers. Pliny says,[1\15] "Why crystal is generated in a hexagonal form, it is difficult to assign a reason; and the more so, since, while its faces are smoother than any art can make them, the pyramidal points are not all of the same kind." The quartz crystals of the Alps, to which he refers, are, in some specimens, very regular, while in others, one side of the pyramid becomes much the largest; yet the angles remain constantly the same. But when the whole shape varied so much, the angles also seemed to vary. Thus Conrad Gessner, a very learned naturalist, who, in 1564, published at Zurich his work, De rerum Fossilium, Lapidum et Gemmarum maxime, Figuris, says,[2\15] "One crystal differs from another in its angles, and consequently in its figure." And Cæsalpinus, who, as we shall find, did so much in establishing fixed characters in botany, was led by some of his general views to disbelieve the fixity of the form of crystals. In his work De Metallicis, published at Nuremberg in 1602, he says,[3\15] "To ascribe to inanimate bodies a definite form, does not appear consentaneous to reason; for it is the office of organization to produce a definite form;" {317} an opinion very natural in one who had been immersed in the study of the general analogies of the forms of plants. But though this is excusable in Cæsalpinus, the rejection of this definiteness of form a hundred years later, when its existence had been proved, and its laws developed by numerous observers, cannot be ascribed to anything but strong prejudice; yet this was the course taken by no less a person than Buffon. "The form of crystallization," says he,[4\15] "is not a constant character, but is more equivocal and more variable than any other of the characters by which minerals are to be distinguished." And accordingly, he makes no use of this most important feature in his history of minerals. This strange perverseness may perhaps be ascribed to the dislike which Buffon is said to have entertained for Linnæus, who had made crystalline form a leading character of minerals.

[Note 1\15: Nat. Hist. xxvii. 2.]

[Note 2\15: p. 25.]

[Note 3\15: p. 97.]

[Note 4\15: Hist. des Min. p. 343.]

It is not necessary to mark all the minute steps by which mineralogists were gradually led to see clearly the nature and laws of the fixity of crystalline forms. These forms were at first noticed in that substance which is peculiarly called rock-crystal or quartz; and afterwards in various stones and gems, in salts obtained from various solutions, and in snow. But those who observed the remarkable regular figures which these substances assume, were at first impelled onwards in their speculations by the natural tendency of the human mind to generalize and guess, rather than to examine and measure. They attempted to snatch at once the general laws of geometrical regularity of these occurrences, or to connect them with some doctrine concerning formative causes. Thus Kepler,[5\15] in his Harmonics of the World, asserts a "formatrix facultas, which has its seat in the entrails of the earth, and, after the manner of a pregnant woman, expresses the five regular geometrical solids in the forms of gems." But Philosophers, in the course of time, came to build more upon observation, and less upon abstract reasonings. Nicolas Steno, a Dane, published, in 1669, a dissertation De Solido intra Solidum Naturaliter contento, in which he says,[6\15] that though the sides of the hexagonal crystal may vary, the angles are not changed. And Dominic Gulielmini, in a Dissertation on Salts, published in 1707, says,[7\15] in a true inductive spirit, "Nature does not employ all figures, but only certain ones of those which are possible; and of these, the determination is not to be fetched from the brain, or proved à priori, but obtained by experiments and observations." And {318} he speaks[8\15] with entire decision on this subject: "Nevertheless since there is here a principle of crystallization, the inclination of the planes and of the angles is always constant." He even anticipates, very nearly, the views of later crystallographers as to the mode in which crystals are formed from elementary molecules. From this time, many persons labored and speculated on this subject; as Cappeller, whose Prodromus Crystallographiæ appeared at Lucern in 1723; Bourguet, who published Lettres Philosophiques sur la Formation de Sels et de Cristaux, at Amsterdam, in 1792; and Henckel, the "Physicus" of the Elector of Saxony, whose Pyritologia came forth in 1725. In this last work we have an example of the description of the various forms of special classes of minerals, (iron pyrites, copper pyrites, and arsenic pyrites;) and an example of the enthusiasm which this apparently dry and laborious study can excite: "Neither tongue nor stone," he exclaims,[9\15] "can express the satisfaction which I received on setting eyes upon this sinter covered with galena; and thus it constantly happens, that one must have more pleasure in what seems worthless rubbish, than in the purest and most precious ores, if we know aught of minerals."

[Note 5\15: Linz. 1619, p. 161.]

[Note 6\15: p. 69.]

[Note 7\15: p. 19.]

[Note 8\15: p. 83.]

[Note 9\15: p. 343.]

Still, however, Henckel[10\15] disclaims the intention of arranging minerals according to their mathematical forms; and this, which may be considered as the first decided step in the formation of crystallographic mineralogy, appears to have been first attempted by Linnæus. In this attempt, however, he was by no means happy; nor does he himself appear to have been satisfied. He begins his preface by saying, "Lithology is not what I plume myself upon." (Lithologia mihi cristas non eriget.) Though his sagacity, as a natural historian, led him to see that crystalline form was one of the most definite, and therefore most important, characters of minerals, he failed in profiting by this thought, because, in applying it, he did not employ the light of geometry, but was regulated by what appeared to him resemblances, arbitrarily selected, and often delusive.[11\15] Thus he derived the form of pyrites from that of vitriol;[12\15] and brought together alum and diamond on account of their common octohedral form. But he had the great merit of animating to this study one to whom, more perhaps than to any other person, it owes its subsequent progress; I mean Romé de Lisle. "Instructed," this writer says, in his preface to his Essais de Crystallographie, "by the works of the celebrated Von Linnée, how {319} greatly the study of the angular form of crystals might become interesting, and fitted to extend the sphere of our mineralogical knowledge, I have followed them in all their metamorphoses with the most scrupulous attention." The views of Linnæus, as to the importance of this character, had indeed been adopted by several others; as John Hill, the King's gardener at Kew, who, in 1777, published his Spathogenesia; and Grignon, who, in 1775, says, "These crystallizations may give the means of finding a new theory of the generation of crystalline gems."

[Note 10\15: p. 167.]

[Note 11\15: Marx. Gesch. p. 97.]

[Note 12\15: Syst. Nat. vi. p. 220.]

The circumstance which threw so much difficulty in the way of those who tried to follow out his thought was, that in consequence of the apparent irregularity of crystals, arising from the extension or contraction of particular sides of the figure, each kind of substance may really appear under many different forms, connected with each other by certain geometrical relations. These may be conceived by considering a certain fundamental form to be cut into new forms in particular ways. Thus if we take a cube, and cut off all the eight corners, till the original faces disappear, we make it an octohedron; and if we stop short of this, we have a figure of fourteen faces, which has been called a cubo-octohedron. The first person who appears distinctly to have conceived this truncation of angles and edges, and to have introduced the word, is Démeste;[13\15] although Wallerius[14\15] had already said, in speaking of the various crystalline forms of calcspar, "I conceive it would be better not to attend to all differences, lest we be overwhelmed by the number." And Werner, in his celebrated work On the External Characters of Minerals,[15\15] had formally spoken of truncation, acuation, and acumination, or replacement by a plane, an edge, a point respectively, (abstumpfung, zuschärfung, zuspitzung,) as ways in which the forms of crystals are modified and often disguised. He applied this process in particular to show the connexion of the various forms which are related to the cube. But still the extension of the process to the whole range of minerals and other crystalline bodies, was due to Romé de Lisle. {320}

[Note 13\15: Lettres, 1779, i. 48.]

[Note 14\15: Systema Mineralogicum, 1772-5, i. 143.]

[Note 15\15: Leipzig, 1774.]

Chapter II

EPOCH OF ROMÉ DE LISLE AND HAÜY.--ESTABLISHMENT OF THE FIXITY OF CRYSTALLINE ANGLES, AND THE SIMPLICITY OF THE LAWS OF DERIVATION.

WE have already seen that, before 1780, several mineralogists had recognized the constancy of the angles of crystals, and had seen (as Démeste and Werner,) that the forms were subject to modifications of a definite kind. But neither of these two thoughts was so apprehended and so developed, as to supersede the occasion for a discoverer who should put forward these principles as what they really were, the materials of a new and complete science. The merit of this step belongs jointly to Romé de Lisle and to Haüy. The former of these two men had already, in 1772, published an Essai de Crystallographie, in which he had described a number of crystals. But in this work his views are still rude and vague; he does not establish any connected sequence of transitions in each kind of substance, and lays little or no stress on the angles. But in 1783, his ideas[16\15] had reached a maturity which, by comparison, excites our admiration. In this he asserts, in the most distinct manner, the invariability of the angles of crystals of each kind, under all the changes of relative dimension which the faces may undergo;[17\15] and he points out that this invariability applies only to the primitive forms, from each of which many secondary forms are derived by various changes.[18\15] Thus we cannot deny him the merit of having taken steady hold on both the handles of this discovery, though something still remained for another to do. Romé pursues his general ideas into detail with great labor and skill. He gives drawings of more than five hundred regular forms (in his first work he had inserted only one hundred and ten; Linnæus only knew forty); and assigns them to their proper substances; for instance, thirty to calcspar, and sixteen to felspar. He also invented and used a goniometer. We cannot doubt that he would have been {321} looked upon as a great discoverer, if his fame had not been dimmed by the more brilliant success of his contemporary Haüy.

[Note 16\15: Cristallographie, ou Description de Formes propres à tous les Corps du Règne Minéral. 3 vols. and 1 vol. of plates.]

[Note 17\15: p. 68.]

[Note 18\15: p. 73.]

Réné-Just Haüy is rightly looked upon as the founder of the modern school of crystallography; for all those who have, since him, pursued the study with success, have taken his views for their basis. Besides publishing a system of crystallography and of mineralogy, far more complete than any which had yet appeared, the peculiar steps in the advance which belong to him are, the discovery of the importance of cleavage, and the consequent expression of the laws of derivation of secondary from primary forms, by means of the decrements of the successive layers of integrant molecules.

The latter of these discoveries had already been, in some measure, anticipated by Bergman, who had, in 1773, conceived a hexagonal prism to be built up by the juxtaposition of solid rhombs on the planes of a rhombic nucleus.[19\15] It is not clear[20\15] whether Haüy was acquainted with Bergman's Memoir, at the time when the cleavage of a hexagonal prism of calcspar, accidentally obtained, led him to the same conception of its structure. But however this might be, he had the indisputable credit of following out this conception with all the vigor of originality, and with the most laborious and persevering earnestness; indeed he made it the business of his life. The hypothesis of a solid, built up of small solids, had this peculiar advantage in reference to crystallography; it rendered a reason of this curious fact;--that a certain series of forms occur in crystals of the same kind, while other forms, apparently intermediate between those which actually occur, are rigorously excluded. The doctrine of decrements explained this; for by placing a number of regularly-decreasing rows of equal solids, as, for instance, of bricks, upon one another, we might form a regular equal-sided triangle, as the gable of a house; and if the breadth of the gable were one hundred bricks, the height of the triangle might be one hundred, or fifty, or twenty-five; but it would be found that if the height were an intermediate number, as fifty-seven, or forty-three, the edge of the wall would become irregular; and such irregularity is assumed to be inadmissible in the regular structure of crystals. Thus this mode of conceiving crystals allows of certain definite secondary forms, and no others.

[Note 19\15: De Formis Crystallorum. Nov. Act. Reg. Soc. Sc. Ups. 1773.]

[Note 20\15: Traité de Minér. 1822, i. 15.]

The mathematical deduction of the dimensions and proportions {322} of these secondary forms;--the invention of a notation to express them;--the examination of the whole mineral kingdom in accordance with these views;--the production of a work[21\15] in which they are explained with singular clearness and vivacity;--are services by which Haüy richly earned the admiration which has been bestowed upon him. The wonderful copiousness and variety of the forms and laws to which he was led, thoroughly exercised and nourished the spirit of deduction and calculation which his discoveries excited in him. The reader may form some conception of the extent of his labors, by being told--that the mere geometrical propositions which he found it necessary to premise to his special descriptions, occupy a volume and a half of his work;--that his diagrams are nearly a thousand in number;--that in one single substance (calcspar) he has described forty-seven varieties of form;--and that he has described one kind of crystal (called by him fer sulfuré parallélique) which has one hundred and thirty-four faces.

[Note 21\15: Traité de Minéralogie, 1801, 5 vols.]

In the course of a long life, he examined, with considerable care, all the forms he could procure of all kinds of mineral; and the interpretation which he gave of the laws of those forms was, in many cases, fixed, by means of a name applied to the mineral in which the form occurred; thus, he introduced such names as équiaxe, métastatique, unibinaire, perihexahèdre, bisalterne, and others. It is not now desirable to apply separate names to the different forms of the same mineral species, but these terms answered the purpose, at the time, of making the subjects of study more definite. A symbolical notation is the more convenient mode of designating such forms, and such a notation Haüy invented; but the symbols devised by him had many inconveniences, and have since been superseded by the systems of other crystallographers.

Another of Haüy's leading merits was, as we have already intimated, to have shown, more clearly than his predecessors had done, that the crystalline angles of substances are a criterion of the substances; and that this is peculiarly true of the angles of cleavage;--that is, the angles of those edges which are obtained by cleaving a crystal in two different directions;--a mode of division which the structure of many kinds of crystals allowed him to execute in the most complete manner. As an instance of the employment of this criterion, I may mention his separation of the sulphates of baryta and strontia, which had {323} previously been confounded. Among crystals which in the collections were ranked together as "heavy spar," and which were so perfect as to admit of accurate measurement, he found that those which were brought from Sicily, and those of Derbyshire, differed in their cleavage angle by three degrees and a half. "I could not suppose," he says,[22\15] "that this difference was the effect of any law of decrement; for it would have been necessary to suppose so rapid and complex a law, that such an hypothesis might have been justly regarded as an abuse of the theory." He was, therefore, in great perplexity. But a little while previous to this, Klaproth had discovered that there is an earth which, though in many respects it resembles baryta, is different from it in other respects; and this earth, from the place where it was found (in Scotland), had been named Strontia. The French chemists had ascertained that the two earths had, in some cases, been mixed or confounded; and Vauquelin, on examining the Sicilian crystals, found that their base was strontia, and not, as in the Derbyshire ones, baryta. The riddle was now read; all the crystals with the larger angle belong to the one, all those with the smaller, to the other, of these two sulphates; and crystallometry was clearly recognized as an authorized test of the difference of substances which nearly resemble each other.

[Note 22\15: Traité, ii. 320.]

Enough has been said, probably, to enable the reader to judge how much each of the two persons, now under review, contributed to crystallography. It would be unwise to compare such contributions to science with the great discoveries of astronomy and chemistry; and we have seen how nearly the predecessors of Romé and Haüy had reached the point of knowledge on which these two crystallographers took their stand. But yet it is impossible not to allow, that in these discoveries, which thus gave form and substance to the science of crystallography, we have a manifestation of no common sagacity and skill. Here, as in other discoveries, were required ideas and facts;--clearness of geometrical conception which could deal with most complex relations of form; a minute and extensive acquaintance with actual crystals; and the talent and habit of referring these facts to the general ideas. Haüy, in particular, was happily endowed for his task. Without being a great mathematician, he was sufficiently a geometer to solve all the problems which his undertaking demanded; and though the mathematical reasoning might have been made more compendious {324} by one who was more at home in mathematical generalization, probably this could hardly have been done without making the subject less accessible and less attractive to persons moderately disciplined in mathematics. In all his reasonings upon particular cases, Haüy is acute and clear; while his general views appear to be suggested rather by a lively fancy than by a sage inductive spirit: and though he thus misses the character of a great philosopher, the vivacity of style, and felicity and happiness of illustration, which grace his book, and which agree well with the character of an Abbé of the old French monarchy, had a great and useful influence on the progress of the subject.

Unfortunately Romé de Lisle and Haüy were not only rivals, but in some measure enemies. The former might naturally feel some vexation at finding himself, in his later years (he died in 1790), thrown into shade by his more brilliant successor. In reference to Haüy's use of cleavage, he speaks[23\15] of "innovators in crystallography, who may properly be called crystalloclasts." Yet he adopted, in great measure, the same views of the formation of crystals by laminæ,[24\15] which Haüy illustrated by the destructive process at which he thus sneers. His sensitiveness was kept alive by the conduct of the Academy of Sciences, which took no notice of him and his labors;[25\15] probably because it was led by Buffon, who disliked Linnæus, and might dislike Romé as his follower; and who, as we have seen, despised crystallography. Haüy revenged himself by rarely mentioning Romé in his works, though it was manifest that his obligations to him were immense; and by recording his errors while he corrected them. More fortunate than his rival, Haüy was, from the first, received with favor and applause. His lectures at Paris were eagerly listened to by persons from all quarters of the world. His views were, in this manner, speedily diffused; and the subject was soon pursued, in various ways, by mathematicians and mineralogists in every country of Europe.

[Note 23\15: Pref. p. xxvii.]

[Note 24\15: T. ii. p. 21.]

[Note 25\15: Marx. Gesch. d. Cryst. 130.]

III. RECEPTION AND CORRECTIONS OF THE HAUÏAN CRYSTALLOGRAPHY

I HAVE not hitherto noticed the imperfections of the crystallographic views and methods of Haüy, because my business in the last section {325} was to mark the permanent additions he made to the science. His system did, however, require completion and rectification in various points; and in speaking of the crystallographers of the subsequent time, who may all be considered as the cultivators of the Hauïan doctrines, we must also consider what they did in correcting them.

The three main points in which this improvement was needed were;--a better determination of the crystalline forms of the special substances;--a more general and less arbitrary method of considering crystalline forms according to their symmetry; and a detection of more general conditions by which the crystalline angle is regulated. The first of these processes may be considered as the natural sequel of the Hauïan epoch: the other two must be treated as separate steps of discovery.

When it appeared that the angle of natural or of cleavage faces could be used to determine the differences of minerals, it became important to measure this angle with accuracy. Haüy's measurements were found very inaccurate by many succeeding crystallographers: Mohs says[26\15] that they are so generally inaccurate, that no confidence can be placed in them. This was said, of course, according to the more rigorous notions of accuracy to which the establishment of Haüy's system led. Among the persons who principally labored in ascertaining, with precision, the crystalline angles of minerals, were several Englishmen, especially Wollaston, Phillips, and Brooke. Wollaston, by the invention of his Reflecting Goniometer, placed an entirely new degree of accuracy within the reach of the crystallographer; the angle of two faces being, in this instrument, measured by means of the reflected images of bright objects seen in them, so that the measure is the more accurate the more minute the faces are. In the use of this instrument, no one was more laborious and successful than William Phillips, whose power of apprehending the most complex forms with steadiness and clearness, led Wollaston to say that he had "a geometrical sense." Phillips published a Treatise on Mineralogy, containing a great collection of such determinations; and Mr. Brooke, a crystallographer of the same exact and careful school, has also published several works of the same kind. The precise measurement of crystalline angles must be the familiar employment of all who study crystallography; and, therefore, any further enumeration of those {326} who have added in this way to the stock of knowledge, would be superfluous.

[Note 26\15: Marx. p. 153.]

Nor need I dwell long on those who added to the knowledge which Haüy left, of derived forms. The most remarkable work of this kind was that of Count Bournon, who published a work on a single mineral (calcspar) in three quarto volumes.[27\15] He has here given representations of seven hundred forms of crystals, of which, however, only fifty-six are essentially different. From this example the reader may judge what a length of time, and what a number of observers and calculators, were requisite to exhaust the subject.

[Note 27\15: Traité complet de la Chaux Carbonatée et d'Aragonite, par M. le Comte de Bournon. London, 1808.]

If the calculations, thus occasioned, had been conducted upon the basis of Haüy's system, without any further generalization, they would have belonged to that process, the natural sequel of inductive discoveries, which we call deduction; and would have needed only a very brief notice here. But some additional steps were made in the upward road to scientific truth, and of these we must now give an account.

Chapter IV

ESTABLISHMENT OF THE DISTINCTION OF SYSTEMS OF CRYSTALLIZATION.--WEISS AND MOHS.

IN Haüy's views, as generally happens in new systems, however true, there was involved something that was arbitrary, something that was false or doubtful, something that was unnecessarily limited. The principal points of this kind were;--his having made the laws of crystalline derivation depend so much upon cleavage;--his having assumed an atomic constitution of bodies as an essential part of his system; and his having taken a set of primary forms, which, being selected by no general view, were partly superfluous, and partly defective.

How far evidence, such as has been referred to by various philosophers, has proved, or can prove, that bodies are constituted of indivisible atoms, will be more fully examined in the work which treats of the Philosophy of this subject. There can be little doubt that the {327} portion of Haüy's doctrine which most riveted popular attention and applause, was his dissection of crystals, in a manner which was supposed to lead actually to their ultimate material elements. Yet it is clear, that since the solids given by cleavage are, in many cases, such as cannot make up a solid space, the primary conception of a necessary geometrical identity between the results of division and the elements of composition, which is the sole foundation of the supposition that crystallography points out the actual elements, disappears on being scrutinized: and when Haüy, pressed by this difficulty, as in the case of fluor-spar, put his integrant octohedral molecules together, touching by the edges only, his method became an empty geometrical diagram, with no physical meaning.

The real fact, divested of the hypothesis which was contained in the fiction of decrements, was, that when the relation of the derivative to the primary faces is expressed by means of numerical indices, these numbers are integers, and generally very small ones; and this was the form which the law gradually assumed, as the method of derivation was made more general and simple by Weiss and others.

"When, in 1809, I published my Dissertation," says Weiss,[28\15] "I shared the common opinion as to the necessity of the assumption and the reality of the existence of a primitive form, at least in a sense not very different from the usual sense of the expression. While I sought," he adds, referring to certain doctrines of general philosophy which he and others entertained, "a dynamical ground for this, instead of the untenable atomistic view, I found that, out of my primitive forms, there was gradually unfolded to my hands, that which really governs them, and is not affected by their casual fluctuations, the fundamental relations of those Dimensions according to which a multiplicity of internal oppositions, necessarily and mutually interdependent, are developed in the mass, each having its own polarity; so that the crystalline character is co-extensive with these polarities."

[Note 28\15: Mem. Acad. Berl. 1816, p. 307.]

The "Dimensions" of which Weiss here speaks, are the Axes of Symmetry of the crystal; that is, those lines in reference to which, every face is accompanied by other faces, having like positions and properties. Thus a rhomb, or more properly a rhombohedron,[29\15] of {328} calcspar may be placed with one of its obtuse corners uppermost, so that all the three faces which meet there are equally inclined to the vertical line. In this position, every derivative face, which is obtained by any modification of the faces or edges of the rhombohedron, implies either three or six such derivative faces; for no one of the three upper faces of the rhombohedron has any character or property different from the other two; and, therefore, there is no reason for the existence of a derivative from one of these primitive faces, which does not equally hold for the other primitive faces. Hence the derivative forms will, in all cases, contain none but faces connected by this kind of correspondence. The axis thus made vertical will be an Axis of Symmetry, and the crystal will consist of three divisions, ranged round this axis, and exactly resembling each other. According to Weiss's nomenclature, such a crystal is "three-and-three-membered."

[Note 29\15: I use this name for the solid figure, since rhomb has always been used for a plane figure.]

But this is only one of the kinds of symmetry which crystalline forms may exhibit. They may have three axes of complete and equal symmetry at right angles to each other, as the cube and the regular octohedron;--or, two axes of equal symmetry, perpendicular to each other and to a third axis, which is not affected with the same symmetry with which they are; such a figure is a square pyramid;--or they may have three rectangular axes, all of unequal symmetry, the modifications referring to each axis separately from the other two.

These are essential and necessary distinctions of crystalline form; and the introduction of a classification of forms founded on such relations, or, as they were called, Systems of Crystallization, was a great improvement upon the divisions of the earlier crystallographers, for those divisions were separated according to certain arbitrarily-assumed primary forms. Thus Romé de Lisle's fundamental forms were, the tetrahedron, the cube, the octohedron, the rhombic prism, the rhombic octohedron, the dodecahedron with triangular faces: Haüy's primary forms are the cube, the rhombohedron, the oblique rhombic prism, the right rhombic prism, the rhombic dodecahedron, the regular octohedron, tetrahedron, and six-sided prism, and the bipyramidal dodecahedron. This division, as I have already said, errs both by excess and defect, for some of these primary forms might be made derivatives from others; and no solid reason could be assigned why they were not. Thus the cube may be derived from the tetrahedron, by truncating the edges; and the rhombic dodecahedron again from the cube, by truncating its edges; while the square pyramid could not be legitimately identified with the derivative of any of these forms; for if we were to {329} derive it from the rhombic prism, why should the acute angles always suffer decrements corresponding in a certain way to those of the obtuse angles, as they must do in order to give rise to a square pyramid?

The introduction of the method of reference to Systems of Crystallization has been a subject of controversy, some ascribing this valuable step to Weiss, and some to Mohs.[30\15] It appears, I think, on the whole, that Weiss first published works in which the method is employed; but that Mohs, by applying it to all the known species of minerals, has had the merit of making it the basis of real crystallography. Weiss, in 1809, published a Dissertation On the mode of investigating the principal geometrical character of crystalline forms, in which he says,[31\15] "No part, line, or quantity, is so important as the axis; no consideration is more essential or of a higher order than the relation of a crystalline plane to the axis;" and again, "An axis is any line governing the figure, about which all parts are similarly disposed, and with reference to which they correspond mutually." This he soon followed out by examination of some difficult cases, as Felspar and Epidote. In the Memoirs of the Berlin Academy,[32\15] for 1814-15, he published An Exhibition of the natural Divisions of Systems of Crystallization. In this Memoir, his divisions are as follows:--The regular system, the four-membered, the two-and-two-membered, the three-and-three-membered, and some others of inferior degrees of symmetry. These divisions are by Mohs (Outlines of Mineralogy, 1822), termed the tessular, pyramidal, prismatic, and rhombohedral systems respectively. Hausmann, in his Investigations concerning the Forms of Inanimate Nature,[33\15] makes a nearly corresponding arrangement;--the isometric, monodimetric, trimetric, and monotrimetic; and one or other of these sets of terms have been adopted by most succeeding writers.

[Note 30\15: Edin. Phil. Trans. 1823, vols. xv. and xvi.]

[Note 31\15: pp. 16, 42.]

[Note 32\15: Ibid.]

[Note 33\15: Göttingen, 1821.]

In order to make the distinctions more apparent, I have purposely omitted to speak of the systems which arise when the prismatic system loses some part of its symmetry;--when it has only half or a quarter its complete number of faces;--or, according to Mohs's phraseology, when it is hemihedral or tetartohedral. Such systems are represented by the singly-oblique or doubly-oblique prism; they are termed by Weiss two-and-one-membered, and one-and-one-membered; by other writers, Monoklinometric, and Triklinometric Systems. There are also other {330} peculiarities of Symmetry, such, for instance, as that of the plagihedral faces of quartz, and other minerals.

The introduction of an arrangement of crystalline forms into systems, according to their degree of symmetry, was a step which was rather founded on a distinct and comprehensive perception of mathematical relations, than on an acquaintance with experimental facts, beyond what earlier mineralogists had possessed. This arrangement was, however, remarkably confirmed by some of the properties of minerals which attracted notice about the time now spoken of, as we shall see in the next chapter.

Chapter V

RECEPTION AND CONFIRMATION OF THE DISTINCTION OF SYSTEMS OF CRYSTALLIZATION.

DIFFUSION OF THE DISTINCTION OF SYSTEMS.--The distinction of systems of crystallization was so far founded on obviously true views, that it was speedily adopted by most mineralogists. I need not dwell on the steps by which this took place. Mr. Haidinger's translation of Mohs was a principal occasion of its introduction in England. As an indication of dates, bearing on this subject, perhaps I may be allowed to notice, that there appeared in the Philosophical Transactions for 1825, A General Method of Calculating the **Angles of Crystals, which I had written, and in which I referred only to Haüy's views; but that in 1826,[34\15] I published a Memoir On the Classification of Crystalline Combinations, founded on the methods of Weiss and Mohs, especially the latter; with which I had in the mean time become acquainted, and which appeared to me to contain their own evidence and recommendation. General methods, such as was attempted in the Memoir just quoted, are part of that process in the history of sciences, by which, when the principles are once established, the mathematical operation of deducing their consequences is made more and more general and symmetrical: which we have seen already exemplified in the history of celestial mechanics after the time of Newton. It does not enter into our plan, to dwell upon the various steps in this way {331} made by Levy, Naumann, Grassmann, Kupffer, Hessel, and by Professor Miller among ourselves. I may notice that one great improvement was, the method introduced by Monteiro and Levy, of determining the laws of derivation of forces by means of the parallelisms of edges; which was afterwards extended so that faces were considered as belonging to zones. Nor need I attempt to enumerate (what indeed it would be difficult to describe in words) the various methods of notation by which it has been proposed to represent the faces of crystals, and to facilitate the calculations which have reference to them.

[Note 34\15: Camb. Trans. vol. ii. p. 391.]

[2nd Ed.] [My Memoir of 1825 depended on the views of Haüy in so far as that I started from his "primitive forms;" but being a general method of expressing all forms by co-ordinates, it was very little governed by these views. The mode of representing crystalline forms which I proposed seemed to contain its own evidence of being more true to nature than Haüy's theory of decrements, inasmuch as my method expressed the faces at much lower numbers. I determine a face by means of the dimensions of the primary form divided by certain numbers; Haüy had expressed the face virtually by the same dimensions multiplied by numbers. In cases where my notation gives such numbers as (3, 4, 1), (1, 3, 7), (5, 1, 19), his method involves the higher numbers (4, 3, 12), (21, 7, 3), (19, 95, 5). My method however has, I believe, little value as a method of "calculating the angles of crystals."

M. Neumann, of Königsberg, introduced a very convenient and elegant mode of representing the position of faces of crystals by corresponding points on the surface of a circumscribing sphere. He gave (in 1823) the laws of the derivation of crystalline faces, expressed geometrically by the intersection of zones, (Beiträge zur Krystallonomie.) The same method of indicating the position of faces of crystals was afterwards, together with the notation, re-invented by M. Grassmann, (Zur Krystallonomie und Geometrischen Combinationslehre, 1829.) Aiding himself by the suggestions of these writers, and partly adopting my method, Prof. Miller has produced a work on Crystallography remarkable for mathematical elegance and symmetry; and has given expressions really useful for calculating the angles of crystalline faces, (A Treatise on Crystallography. Cambridge, 1839.)]

Confirmation of the Distinction of Systems by the Optical Properties of Minerals.--Brewster.--I must not omit to notice the striking confirmation which the distinction of systems of crystallization received from optical discoveries, especially those of Sir D. Brewster. Of the {332} history of this very rich and beautiful department of science, we have already given some account, in speaking of Optics. The first facts which were noticed, those relating to double refraction, belonged exclusively to crystals of the rhombohedral system. The splendid phenomena of the rings and lemniscates produced by dipolarizing crystals, were afterwards discovered; and these were, in 1817, classified by Sir David Brewster, according to the crystalline forms to which they belong. This classification, on comparison with the distinction of Systems of Crystallization, resolved itself into a necessary relation of mathematical symmetry: all crystals of the pyramidal and rhombohedral systems, which from their geometrical character have a single axis of symmetry, are also optically uniaxal, and produce by dipolarization circular rings; while the prismatic system, which has no such single axis, but three unequal axes of symmetry, is optically biaxal, gives lemniscates by dipolarized light, and according to Fresnel's theory, has three rectangular axes of unequal elasticity.

[2nd Ed.] [I have placed Sir David Brewster's arrangement of crystalline forms in this chapter, as an event belonging to the confirmation of the distinctions of forms introduced by Weiss and Mohs; because that arrangement was established, not on crystallographical, but on optical grounds. But Sir David Brewster's optical discovery was a much greater step in science than the systems of the two German crystallographers; and even in respect to the crystallographical principle, Sir D. Brewster had an independent share in the discovery. He divided crystalline forms into three classes, enumerating the Hauïan "primitive forms" which belonged to each; and as he found some exceptions to this classification, (such as idocrase, &c.,) he ventured to pronounce that in those substances the received primitive forms were probably erroneous; a judgment which was soon confirmed by a closer crystallographical scrutiny. He also showed his perception of the mineralogical importance of his discovery by publishing it, not only in the Phil. Trans. (1818), but also in the Transactions of the Wernerian Society of Natural History. In a second paper inserted in this later series, read in 1820, he further notices Mohs's System of Crystallography, which had then recently appeared, and points out its agreement with his own.

Another reason why I do not make his great optical discovery a cardinal point in the history of crystallography is, that as a crystallographical system it is incomplete. Although we are thus led to distinguish the tessular and the prismatic systems (using Mohs's terms) {333} from the rhombohedral and the square prismatic, we are not led to distinguish the latter two from each other; inasmuch as they have no optical difference of character. But this distinction is quite essential in crystallography; for these two systems have faces formed by laws as different as those of the other two systems.

Moreover, Weiss and Mohs not only divided crystalline forms into certain classes, but showed that by doing this, the derivation of all the existing forms from the fundamental ones assumed a new aspect of simplicity and generality; and this was the essential part of what they did.

On the other hand, I do not think it is too much to say as I have elsewhere said[35\15] that "Sir D. Brewster's optical experiments must have led to a classification of crystals into the above systems, or something nearly equivalent, even if crystals had not been so arranged by attention to their forms."]

[Note 35\15: Philosophy of the Inductive Sciences, B. viii. C. iii. Art. 3.]

Many other most curious trains of research have confirmed the general truth, that the degree and kind of geometrical symmetry corresponds exactly with the symmetry of the optical properties. As an instance of this, eminently striking for its singularity, we may notice the discovery of Sir John Herschel, that the plagihedral crystallization of quartz, by which it exhibits faces twisted to the right or the left, is accompanied by right-handed or left-handed circular polarization respectively. No one acquainted with the subject can now doubt, that the correspondence of geometrical and optical symmetry is of the most complete and fundamental kind.

[2nd Ed.] [Our knowledge with respect to the positions of the optical axes of the oblique prismatic crystals is still imperfect. It appears to be ascertained that, in singly oblique crystals, one of the axes of optical elasticity coincides with the rectangular crystallographic axis. In doubly oblique crystals, one of the axes of optical elasticity is, in many cases, coincident with the axis of a principal zone. I believe no more determinate laws have been discovered.]

Thus the highest generalization at which mathematical crystallographers have yet arrived, may be considered as fully established; and the science of Crystallography, in the condition in which these place it, is fit to be employed as one of the members of Mineralogy, and thus to fill its appropriate place and office. {334}

Chapter VI

CORRECTION OF THE LAW OF THE SAME ANGLE FOR THE SAME SUBSTANCE.

DISCOVERY OF ISOMORPHISM. MITSCHERLICH.--The discovery of which we now have to speak may appear at first sight too large to be included in the history of crystallography, and may seem to belong rather to chemistry. But it is to be recollected that crystallography, from the time of its first assuming importance in the hands of Haüy, founded its claim to notice entirely upon its connexion with chemistry; crystalline forms were properties of something; but what that something was, and how it might be modified without becoming something else, no crystallographer could venture to decide, without the aid of chemical analysis. Haüy had assumed, as the general result of his researches, that the same chemical elements, combined in the same proportions, would always exhibit the same crystalline form; and reciprocally, that the same form and angles (except in the obvious case of the tessular system, in which the angles are determined by its being the tessular system,) implied the same chemical constitution. But this dogma could only be considered as an approximate conjecture; for there were many glaring and unexplained exceptions to it. The explanation of several of these was beautifully described by the discovery that there are various elements which are isomorphous to each other; that is, such that one may take the place of another without altering the crystalline form; and thus the chemical composition may be much changed, while the crystallographic character is undisturbed.

This truth had been caught sight of, probably as a guess only, by Fuchs as early as 1815. In speaking of a mineral which had been called Gehlenite, he says, "I hold the oxide of iron, not for an essential component part of this genus, but only as a vicarious element, replacing so much lime. We shall find it necessary to consider the results of several analyses of mineral bodies in this point of view, if we wish, on the one hand, to bring them into agreement with the doctrine of chemical proportions, and on the other, to avoid unnecessarily splitting up genera." In a lecture On the Mutual Influence of {335} Chemistry and Mineralogy,[36\15] he again draws attention to his term vicarious (vicarirende), which undoubtedly expresses the nature of the general law afterwards established by Mitscherlich in 1822.

[Note 36\15: Munich, 1820.]

But Fuchs's conjectural expression was only a prelude to Mitscherlich's experimental discovery of isomorphism. Till many careful analyses had given substance and signification to this conception of vicarious elements, it was of small value. Perhaps no one was more capable than Berzelius of turning to the best advantage any ideas which were current in the chemical world; yet we find him,[37\15] in 1820, dwelling upon a certain vague view of these cases,--that "oxides which contain equal doses of oxygen must have their general properties common;" without tracing it to any definite conclusions. But his scholar, Mitscherlich, gave this proposition a real crystallographical import. Thus he found that the carbonates of lime (calcspar,) of magnesia, of protoxide of iron, and of protoxide of manganese, agree in many respects of form, while the homologous angles vary through one or two degrees only; so again the carbonates of baryta, strontia, lead, and lime (arragonite), agree nearly; the different kinds of felspar vary only by the substitution of one alkali for another; the phosphates are almost identical with the arseniates of several bases. These, and similar results, were expressed by saying that, in such cases, the bases, lime, protoxide of iron, and the rest, are isomorphous; or in the latter instance, that the arsenic and phosphoric acids are isomorphous.

[Note 37\15: Essay on the Theory of Chemical Proportions, p. 122.]

Since, in some of these cases, the substitution of one element of the isomorphous group for another does alter the angle, though slightly, it has since been proposed to call such groups plesiomorphous.

This discovery of isomorphism was of great importance, and excited much attention among the chemists of Europe. The history of its reception, however, belongs, in part, to the classification of minerals; for its effect was immediately to metamorphose the existing chemical systems of arrangement. But even those crystallographers and chemists who cared little for general systems of classification, received a powerful impulse by the expectation, which was now excited, of discovering definite laws connecting chemical constitution with crystalline form. Such investigations were soon carried on with great activity. Thus, at a recent period, Abich analysed a number of tessular minerals, spinelle, pleonaste, gahnite, franklinite, and chromic iron oxide; and {336} seems to have had some success in **giving a common type to their chemical formulæ, as there is a common type in their crystallization.

[2nd Ed.] [It will be seen by the above account that Prof. Mitscherlich's merit in the great discovery of Isomorphism is not at all narrowed by the previous conjectures of M. Fuchs. I am informed, moreover, that M. Fuchs afterwards (in Schweigger's Journal) retracted the opinions he had put forward on this subject.]

Dimorphism.--My business is, to point out the connected truths which have been obtained by philosophers, rather than insulated difficulties which still stand out to perplex them. I need not, therefore, dwell on the curious cases of dimorphism; cases in which the same definite chemical compound of the same elements appears to have two different forms; thus the carbonate of lime has two forms, calcspar and arragonite, which belong to different systems of crystallization. Such facts may puzzle us; but they hardly interfere with any received general truths, because we have as yet no truths of very high order respecting the connexion of chemical constitution and crystalline form. Dimorphism does not interfere with isomorphism; the two classes of facts stand at the same stage of inductive generalization, and we wait for some higher truth which shall include both, and rise above them.

[2nd Ed.] [For additions to our knowledge of the Dimorphism of Bodies, see Professor Johnstone's valuable Report on that subject in the Reports of the British Association for 1837. Substances have also been found which are trimorphous. We owe to Professor Mitscherlich the discovery of dimorphism, as well as of isomorphism: and to him also we owe the greater part of the knowledge to which these discoveries have led.]

Chapter VII

ATTEMPTS TO ESTABLISH THE FIXITY OF OTHER PHYSICAL PROPERTIES.--WERNER.

THE reflections from which it appeared, (at the end of the last Book,) that in order to obtain general knowledge respecting bodies, we must give scientific fixity to our appreciation of their properties, applies to their other properties as well as to their crystalline {337} form. And though none of the other properties have yet been referred to standards so definite as that which geometry supplies for crystals, a system has been introduced which makes their measures far more constant and precise than they are to a common undisciplined sense.

The author of this system was Abraham Gottlob Werner, who had been educated in the institutions which the Elector of Saxony had established at the mines of Freiberg. Of an exact and methodical intellect, and of great acuteness of the senses, Werner was well fitted for the task of giving fixity to the appreciation of outward impressions; and this he attempted in his Dissertation on the external Characters of Fossils, which was published at Leipzig in 1774. Of the precision of his estimation of such characters, we may judge from the following story, told by his biographer Frisch.[38\15] One of his companions had received a quantity of pieces of amber, and was relating to Werner, then very young, that he had found in the lot one piece from which he could extract no signs of electricity. Werner requested to be allowed to put his hand in the bag which contained these pieces, and immediately drew out the unelectrical piece. It was yellow chalcedony, which is distinguishable from amber by its weight and coldness.

[Note 38\15: Werner's Leben, p. 26.]

The principal external characters which were subjected by Werner to a systematic examination were color, lustre, hardness, and specific gravity. His subdivisions of the first character (Color), were very numerous; yet it cannot be doubted that if we recollect them by the eye, and not by their names, they are definite and valuable characters, and especially the metallic colors. Breithaupt, merely by the aid of this character, distinguished two new compounds among the small grains found along with the grains of platinum, and usually confounded with them. The kinds of Lustre, namely, glassy, fatty, adamantine, metallic, are, when used in the same manner, equally valuable. Specific Gravity obviously admits of a numerical measure; and the Hardness of a mineral was pretty exactly defined by the substances which it would scratch, and by which it was capable of being scratched.

Werner soon acquired a reputation as a mineralogist, which drew persons from every part of Europe to Freiberg in order to hear his lectures; and thus diffused very widely his mode of employing external characters. It was, indeed, impossible to attend so closely to {338} these characters as the Wernerian method required, without finding that they were more distinctive than might at first sight be imagined; and the analogy which this mode of studying Mineralogy established between that and other branches of Natural History, recommended the method to those in whom a general inclination to such studies was excited. Thus Professor Jameson of Edinburgh, who had been one of the pupils of Werner at Freiberg, not only published works in which he promulgated the mineralogical doctrines of his master, but established in Edinburgh a "Wernerian Society," having for its object the general cultivation of Natural History.

Werner's standards and nomenclature of external characters were somewhat modified by Mohs, who, with the same kinds of talents and views, succeeded him at Freiberg. Mohs reduced hardness to numerical measure by selecting ten known minerals, each harder than the other in order, from talc to corundum and diamond, and by making the place which these minerals occupy in the list, the numerical measure of the hardness of those which are compared with them. The result of the application of this fixed measurement and nomenclature of external characters will appear in the History of Classification, to which we now proceed.

{{339}} SYSTEMATIC MINERALOGY.

VIII. ATTEMPTS AT THE CLASSIFICATION OF MINERALS

Sect. 1.--Proper object of Classification.

THE fixity of the crystalline and other physical properties of minerals is turned to account by being made the means of classifying such objects. To use the language of Aristotle,[39\15] Classification is the architectonic science, to which Crystallography and the Doctrine of External Characters are subordinate and ministerial, as the art of the bricklayer and carpenter are to that of the architect. But classification itself is useful only as subservient to an ulterior science, which shall furnish us with knowledge concerning things so classified. To classify is to divide and to name; and the value of the Divisions which we thus make, and of the names which we give them, is this;--that they render exact knowledge and general propositions possible. Now the knowledge which we principally seek concerning minerals is a knowledge of their chemical composition; the general propositions to which we hope to be led are such as assert relations between their intimate constitution and their external attributes. Thus our Mineralogical Classification must always have an eye turned towards Chemistry. We cannot get rid of the fundamental conviction, that the elementary composition of bodies, since it fixes their essence, must determine their properties. Hence all mineralogical arrangements, whether they profess it or not, must be, in effect, chemical; they must have it for their object to bring into view a set of relations, which, whatever else they may be, are at least chemical relations. We may begin with the outside, but it is only in order to reach the inner {340} structure. We may classify without reference to chemistry; but if we do so, it is only that we may assert chemical propositions with reference to our classification.

[Note 39\15: Eth. Nicom. i. 2.]

But, as we have already attempted to show, we not only may, but we must classify, by other than chemical characters, in order to be able to make our classification the basis of chemical knowledge. In order to assert chemical truths concerning bodies, we must have the bodies known by some tests not chemical. The chemist cannot assert that Arragonite does or does not contain Strontia, except the mineralogist can tell him whether any given specimen is or is not Arragonite. If chemistry be called upon to supply the definitions as well as the doctrines of mineralogy, the science can only consist of identical propositions.

Yet chemistry has been much employed in mineralogical classifications, and, it is generally believed, with advantage to the science: How is this consistent with what has been said?

To this the answer is, that when this has been done with advantage, the authority of external characters, as well as of chemical constitution, has really been brought into play. We have two sets of properties to compare, chemical and physical; to exhibit the connexion of these is the object of scientific mineralogy. And though this connexion would be most distinctly asserted, if we could keep the two sets of properties distinct, yet it may be brought into view in a great degree, by classifications in which both are referred to as guides. Since the governing principle of the attempts at classification is the conviction that the chemical constitution and the physical properties have a definite relation to each other, we appear entitled to use both kinds of evidence, in proportion as we can best obtain each; and then the general consistency and convenience of our system will be the security for its containing substantial knowledge, though this be not presented in a rigorously logical or systematic form.

Such mixed systems of classification, resting partly on chemical and partly on physical characters, naturally appeared as the earliest attempts in this way, before the two members of the subject had been clearly separated in men's minds; and these systems, therefore, we must first give an account of.

Sect. 2.--Mixed Systems of Classification.

Early Systems.--The first attempts at classifying minerals went upon the ground of those differences of general aspect which had been {341} recognized in the formation of common language; as earths, stones, metals. But such arrangements were manifestly vague and confused; and when chemistry had advanced to power and honor, her aid was naturally called in to introduce a better order. "Hiarne and Bromell were, as far as I know," says[40\15] Cronstedt, "the first who founded any mineral system upon chemical principles; to them we owe the three known divisions of the most simple mineral bodies; viz., the calcarei, vitrescentes, and apyri." But Cronstedt's own Essay towards a System of Mineralogy, published in Swedish in 1758, had perhaps more influence than any other, upon succeeding systems. In this, the distinction of earths and stones, and also of vitrescent and non-vitrescent earths (apyri), is rejected. The earths are classed as calcareous, siliceous, argillaceous, and the like. Again, calcareous earth is pure (calc spar), or united with acid of vitriol (gypsum), or united with the muriatic add (sal ammoniac), and the like. It is easy to see that this is the method, which, in its general principle, has been continued to our own time. In such methods, it is supposed that we can recognize the substance by its general appearance, and on this assumption, its place in the system conveys to us chemical knowledge concerning it.

[Note 40\15: Mineralogy, Pref. p. viii.]

But as the other branches of Natural History, and especially Botany, assumed a systematic form, many mineralogists became dissatisfied with this casual and superficial mode of taking account of external characters; they became convinced, that in Mineralogy as in other sciences, classification must have its system and its rules. The views which Werner ascribes to his teacher, Pabst van Ohain,[41\15] show the rise of those opinions which led through Werner to Mohs: "He was of opinion that a natural mineral system must be constructed by chemical determinations, and external characters at the same time (methodus mixta); but that along with this, mineralogists ought also to construct and employ what he called an artificial system, which might serve us as a guide (loco indicis) how to introduce newly-discovered fossils into the system, and how to find easily and quickly those already known and introduced." Such an artificial system, containing not the grounds of classification, but marks for recognition, was afterwards attempted by Mohs, and termed by him the Characteristic of his system.

[Note 41\15: Frisch. Werner's Leben, p. 15.]

Werner's System.--But, in the mean time, Werner's classification had an extensive reign, and this was still a mixed system. Werner himself, indeed, never published a system of mineralogy. "We might {342} almost imagine," Cuvier says,[42\15] "that when he had produced his nomenclature of external characters, he was affrighted with his own creation; and that the reason of his writing so little after his first essay, was to avoid the shackles which he had imposed upon others." His system was, indeed, made known both in and out of Germany, by his pupils; but in consequence of Werner's unwillingness to give it on his own authority, it assumed, in its published forms, the appearance of an extorted secret imperfectly told. A Notice of the Mineralogical Cabinet of Mine-Director Pabst von Ohain, was, in 1792, published by Karsten and Hoffman, under Werner's direction; and conveyed by example, his views of mineralogical arrangement; and[43\15] in 1816 his Doctrine of Classification was surreptitiously copied from his manuscript, and published in a German Journal, termed The Hesperus. But it was only in 1817, after his death, that there appeared Werner's Last Mineral System, edited from his papers by Breithaupt and Köhler: and by this time, as we shall soon see, other systems were coming forwards on the stage.

[Note 42\15: Cuv. El. ii. 314.]

[Note 43\15: Frisch. p. 52.]

A very slight notice of Werner's arrangement will suffice to show that it was, as we have termed it, a Mixed System. He makes four great Classes of fossils, Earthy, Saline, Combustible, Metallic: the earthy fossils are in eight Genera--Diamond, Zircon, Silica, Alumina, Talc, Lime, Baryta, Hallites. It is clear that these genera are in the main chemical, for chemistry alone can definitely distinguish the different Earths which characterize them. Yet the Wernerian arrangement supposed the distinctions to be practically made by reference to those external characters which the teacher himself could employ with such surpassing skill. And though it cannot be doubted, that the chemical views which prevailed around him had a latent influence on his classification in some cases, he resolutely refused to bend his system to the authority of chemistry. Thus,[44\15] when he was blamed for having, in opposition to the chemists, placed diamond among the earthy fossils, he persisted in declaring that, mineralogically considered, it was a stone, and could not be treated as anything else.

[Note 44\15: Frisch. p. 62.]

This was an indication to that tendency, which, under his successor, led to a complete separation of the two grounds of classification. But before we proceed to this, we must notice what was doing at this period in other parts of Europe.

Haüy's System.--Though Werner, on his own principles, ought to {343} have been the first person to see the immense value of the most marked of external characters, crystalline form, he did not, in fact, attach much importance to it. Perhaps he was in some measure fascinated by a fondness for those characters which he had himself systematized, and the study of which did not direct him to look for geometrical relations. However this may be, the glory of giving to Crystallography its just importance in Mineralogy is due to France: and the Treatise of Haüy, published in 1801, is the basis of the best succeeding works of mineralogy. In this work, the arrangement is professedly chemical; and the classification thus established is employed as the means of enunciating crystallographic and other properties. "The principal object of this Treatise," says the author,[45\15] "is the exposition and development of a method founded on certain principles, which may serve as a frame-work for all the knowledge which Mineralogy can supply, aided by the different sciences which can join hands with her and march on the same line.**" It is worthy of notice, as characteristic of this period of Mixed Systems, that the classification of Haüy, though founded on principles so different from the Wernerian ones, deviates little from it in the general character of the divisions. Thus, the first Order of the first Class of Haüy is Acidiferous Earthy Substances; the first genus is Lime; the species are, Carbonate of Lime, Phosphate of Lime, Fluate of Lime, Sulphate of Lime, and so on.

[Note 45\15: Disc. Prél. p. xvii.]

Other Systems.--Such mixed methods were introduced also into this country, and have prevailed, we may say, up to the present time. The Mineralogy of William Phillips, which was published in 1824, and which was an extraordinary treasure of crystallographic facts, was arranged by such a mixed system; that is, by a system professedly chemical; but, inasmuch as a rigid chemical system is impossible, and the assumption of such a one leads into glaring absurdities, the system was, in this and other attempts of the same kind, corrected by the most arbitrary and lax application of other considerations.

It is a curious example of the difference of national intellectual character, that the manifest inconsistencies of the prevalent systems, which led in Germany, as we shall see, to bold and sweeping attempts at reform, produced in England a sort of contemptuous despair with regard to systems in general;--a belief that no system could be consistent or useful;--and a persuasion that the only valuable knowledge is the accumulation of particular facts. This is not the place to {344} explain how erroneous and unphilosophical such an opinion is. But we may notice that while such a temper prevails among us, our place in this science can never be found in advance of that position which we are now considering as exemplified in the period of Werner and Haüy. So long as we entertain such views respecting the objects of Mineralogy, we can have no share in the fortunes of the succeeding period of its history, to which I now proceed.

Chapter IX

ATTEMPTS AT THE REFORM OF MINERALOGICAL SYSTEMS.--SEPARATION OF THE CHEMICAL AND NATURAL HISTORY METHODS.

Sect. 1.--Natural History System of Mohs.

THE chemical principle of classification, if pursued at random, as in the cases just spoken of leads to results at which a philosophical spirit revolts; it separates widely substances which are not distinguishable; joins together bodies the most dissimilar; and in hardly any instance does it bring any truth into view. The vices of classifications like that of Haüy could not long be concealed; but even before time had exposed the weakness of his system, Haüy himself had pointed out, clearly and without reserve,[46\15] that a chemical system is only one side of the subject, and supposes, as its counterpart, a science of external characters. In the mean time, the Wernerians were becoming more and more in love with the form which they had given to such a science. Indeed, the expertness which Werner and his scholars acquired in the use of external characters, justified some partiality for them. It is related of him,[47\15] that, by looking at a piece of iron-ore, and poising it in his hand, he was able to tell, almost precisely, the proportion of pure metal which it contained. And in the last year of his life,[48\15] he had marked out, as the employment of the ensuing winter, the study of the system of Berzelius, with a view to find out the laws of combination as disclosed by external characters. In the same spirit, his pupil {345} Breithaupt[49\15] attempted to discover the ingredients of minerals by their peculiarities of crystallization. The persuasion that there must be some connexion between composition and properties, transformed itself, in their minds, into a belief that they could seize the nature of the connexion by a sort of instinct.

[Note 46\15: See his Disc. Prél.]

[Note 47\15: Frisch. Werner's Leben, p. 78.]

[Note 48\15: Frisch. 3.]

[Note 49\15: Dresdn. Auswahl, vol. ii. p. 97.]

This opinion of the independency of the science of external characters, and of its sufficiency for its own object, at last assumed its complete form in the bold attempt to construct a system which should borrow nothing from chemistry. This attempt was made by Frederick Mohs, who had been the pupil of Werner, and was afterwards his successor in the school of Freiberg; and who, by the acute and methodical character of his intellect, and by his intimate knowledge of minerals, was worthy of his predecessor. Rejecting altogether all divisions of which the import was chemical, Mohs turned for guidance, or at least for the light of analogy, to botany. His object was to construct a Natural System of mineralogy. What the conditions and advantages of a natural system of any province of nature are, we must delay to explain till we have before us, in botany, a more luminous example of such a scheme. But further; in mineralogy, as in botany, besides the Natural System, by which we form our classes, it is necessary to have an Artificial System by which we recognize them;--a principle which, we have seen, had already taken root in the school of Freiberg. Such an artificial system Mohs produced in his Characteristic of the Mineral Kingdom, which was published at Dresden in 1820; and which, though extending only to a few pages, excited a strong interest in Germany, where men's minds were prepared to interpret the full import of such a work. Some of the traits of such a "Characteristic" had, indeed, been previously drawn by others; as for example, by Haüy, who notices that each of his Classes has peculiar characters. For instance, his First Class (acidiferous substances,) alone possesses these combinations of properties; "division into a regular octohedron, without being able to scratch glass; specific gravity above 3·5, without being able to scratch glass." The extension of such characters into a scheme which should exhaust the whole mineral kingdom, was the undertaking of Mohs.

Such a collection of marks of classes, implied a classification previously established, and accordingly, Mohs had created his own mineral system. His aim was to construct it, as we shall hereafter see that other natural systems are constructed, by taking into account all the {346} resemblances and differences of the objects classified. It is obvious that to execute such a work, implied a most intimate and universal acquaintance with minerals;--a power of combining in one vivid survey the whole mineral kingdom. To illustrate the spirit in which Professor Mohs performed his task, I hope I may be allowed to refer to my own intercourse with him. At an early period of my mineralogical studies, when the very conception of a Natural System was new to me, he, with great kindliness of temper, allowed me habitually to propose to him the scruples which arose in my mind, before I could admit principles which appeared to me then so vague and indefinite; and answered my objections with great patience and most instructive clearness. Among other difficulties, I one day propounded to him this;--"You have published a Treatise on Mineralogy, in which you have described all the important properties of all known minerals. On your principles, then, it ought to be possible, merely by knowing the descriptions in your book, and without seeing any minerals, to construct a natural system; and this natural system ought to turn out identical with that which you have produced, by so careful an examination of the minerals themselves." He pondered a moment, and then he answered, "It is true; but what an enormous imagination (einbildungskraft, power of inward imagining), a man must have for such a work!" Vividness of conception of sensible properties, and the steady intuition (anschauung) of objects, were deemed by him, and by the Wernerian school in general, to be the most essential conditions of complete knowledge.

It is not necessary to describe Mohs's system in detail; it may sufficiently indicate its form to state that the following substances, such as I before gave as examples of other arrangements, calcspar, gypsum, fluor spar, apatite, heavy spar, are by Mohs termed respectively, Rhombohedral Lime Haloide, Gyps Haloide, Octohedral Fluor Haloide, Rhombohedral Fluor Haloide, Prismatic Hal Baryte. These substances are thus referred to the Orders Haloide, and Baryte; to Genera Lime Haloide, Fluor Haloide, Hal Baryte; and the Species is an additional particularization.

Mohs not only aimed at framing such a system, but was also ambitious of giving to all minerals Names which should accord with the system. This design was too bold to succeed. It is true, that a new nomenclature was much needed in mineralogy: it is true, too, that it was reasonable to expect, from an improved classification, an improved nomenclature, such as had been so happily obtained in botany by the {347} reform of Linnæus. But besides the defects of Mohs's system, he had not prepared his verbal novelties with the temperance and skill of the great botanical reformer. He called upon mineralogists to change the name of almost every mineral with which they were acquainted; and the proposed appellations were mostly of a cumbrous form, as the above example may serve to show. Such names could have obtained general currency, only after a general and complete acceptance of the system; and the system did not possess, in a sufficient degree, that evidence which alone could gain it a home in the belief of philosophers,--the coincidence of its results with those of Chemistry. But before I speak finally of the fortunes of the Natural-history System, I will say something of the other attempt which was made about the same time to introduce a Reform into Mineralogy from the opposite extremity of the science.

Sect. 2.--Chemical System of Berzelius and others.

IF the students of external characters were satisfied of the independence of their method, the chemical analysts were naturally no less confident of the legitimate supremacy of their principles: and when the beginning of the present century had been distinguished by the establishment of the theory of definite proportions, and by discoveries which pointed to the electro-chemical theory, it could not appear presumption to suppose, that the classification of bodies, so far as it depended on chemistry, might be presented in a form more complete and scientific than at any previous time.

The attempt to do this was made by the great Swedish chemist Jacob Berzelius. In 1816, he published his Essay to establish a purely Scientific System of Mineralogy, by means of the Application of the Electro-chemical Theory and the Chemical Doctrine of Definite Proportions. It is manifest that, for minerals which are constituted by the law of Definite Proportions, this constitution must be a most essential part of their character. The electro-chemical theory was called in aid, in addition to the composition, because, distinguishing the elements of all compounds as electro-positive and electro-negative, and giving to every element a place in a series, and a place defined by the degree of these relations, it seemed to afford a rigorous and complete principle of arrangement. Accordingly, Berzelius, in his First System, arranged minerals according to their electro-positive element, and the elements according to their electro-positive rank; {348} and supposed that he had thus removed all that was arbitrary and vague in the previous chemical systems of mineralogy.

Though the attempt appeared so well justified by the state of chemical science, and was so plausible in its principle, it was not long before events showed that there was some fallacy in these specious appearances. In 1820, Mitscherlich discovered Isomorphism: by that discovery it appeared that bodies containing very different electro-positive elements could not be distinguished from each other; it was impossible, therefore, to put them in distant portions of the classification;--and thus the first system of Berzelius crumbled to pieces.

But Berzelius did not so easily resign his project. With the most unhesitating confession of his first failure, but with undaunted courage, he again girded himself to the task of rebuilding his edifice. Defeated at the electro-positive position, he now resolved to make a stand at the electro-negative element. In 1824, he published in the Transactions of the Swedish Academy, a Memoir On the Alterations in the Chemical Mineral System, which necessarily follow from the Property exhibited by Isomorphous Bodies, of replacing each other in given Proportions. The alteration was, in fact, an inversion of the system, with an attempt still to preserve the electro-chemical principle of arrangement. Thus, instead of arranging metallic minerals according to the metal, under iron, copper, &c., all the sulphurets were classed together, all the oxides together, all the sulphates together, and so in other respects. That such an order was a great improvement on the preceding one, cannot be doubted; but we shall see, I think, that as a strict scientific system it was not successful. The discovery of isomorphism, however, naturally led to such attempts. Thus Gmelin also, in 1825, published a mineral system,[50\15] which, like that of Berzelius, founded its leading distinctions on the electro-negative, or, as it was sometimes termed, the formative element of bodies; and, besides this, took account of the numbers of atoms or proportions which appear in the composition of the body; distinguishing, for instance, Silicates, as simple silicates, double silicates, and so on, to quintuple silicate (Pechstein) and sextuple silicate (Perlstein). In like manner, Nordenskiöld devised a system resting on the same bases, taking into account also the crystalline form. In 1824, Beudant published his Traité Elémentaire de Minéralogie, in which he professes to found his arrangement on the electro-negative element, and on Ampère's circular {349} arrangement of elementary substances. Such schemes exhibit rather a play of the mere logical faculty, exercising itself on assumed principles, than any attempt at the real interpretation of nature. Other such pure chemical systems may have been published, but it is not necessary to accumulate instances. I proceed to consider their result.

[Note 50\15: Zeitsch. der Min. 1825, p. 435.]

Sect. 3.--Failure of the Attempts at Systematic Reform.

IT may appear presumptuous to speak of the failure of those whom, like Berzelius and Mohs, we acknowledge as our masters, at a period when, probably, they and some of their admirers still hold them to have succeeded in their attempt to construct a consistent system. But I conceive that my office as an historian requires me to exhibit the fortunes of this science in the most distinct form of which they admit, and that I cannot evade the duty of attempting to seize the true aspect of recent occurrences in the world of science. Hence I venture to speak of the failure of both the attempts at framing a pure scientific system of mineralogy,--that founded on the chemical, and that founded on the natural-history principle; because it is clear that they have not obtained that which alone we could, according to the views here presented, consider as success,--a coincidence of each with the other. A Chemical System of arrangement, which should bring together, in all cases, the substances which come nearest each other in external properties;--a Natural-history System, which should be found to arrange bodies in complete accordance with their chemical constitution:--if such systems existed, they might, with justice, claim to have succeeded. Their agreement would be their verification. The interior and exterior system are the type and the antitype, and their entire correspondence would establish the mode of interpretation beyond doubt. But nothing less than this will satisfy the requisitions of science. And when, therefore, the chemical and the natural-history system, though evidently, as I conceive, tending towards each other, are still far from coming together, it is impossible to allow that either method has been successful in regard to its proper object.

But we may, I think, point out the fallacy of the principles, as well as the imperfection of the results, of both of those methods. With regard to that of Berzelius, indeed, the history of the subject obviously betrays its unsoundness. The electro-positive principle was, in a very short time after its adoption, proved and acknowledged to be utterly untenable: what security have we that the electro-negative element is {350} more trustworthy? Was not the necessity of an entire change of system, a proof that the ground, whatever that was, on which the electro-chemical principle was adopted, was an unfounded assumption? And, in fact, do we not find that the same argument which was allowed to be fatal to the First System of Berzelius, applies in exactly the same manner against the Second? If the electro-positive elements be often isomorphous, are not the electro-negative elements sometimes isomorphous also? for instance, the arsenic and phosphoric acids. But to go further, what is the ground on which the electro-chemical arrangement is adopted? Granted that the electrical relations of bodies are important; but how do we come to know that these relations have anything to do with mineralogy? How does it appear that on them, principally, depend those external properties which mineralogy must study? How does it appear that because sulphur is the electro-negative part of one body, and an acid the electro-negative part of another, these two elements similarly affect the compounds? How does it appear that there is any analogy whatever in their functions? We allow that the composition must, in some way, determine the classified place of the mineral,--but why in this way?

I do not dwell on the remark which Berzelius himself[51\15] makes on Nordenskiöld's system;--that it assumes a perfect knowledge of the composition in every case; although, considering the usual discrepancies of analyses of minerals, this objection must make all pure chemical systems useless. But I may observe, that mineralogists have not yet determined what characters are sufficiently affixed to determine a species of minerals. We have seen that the ancient notion of the composition of a species, has been unsettled by the discovery of isomorphism. The tenet of the constancy of the angle is rendered doubtful by cases of plesiomorphism. The optical properties, which are so closely connected with the crystalline, are still so imperfectly known, that they are subject to changes which appear capricious and arbitrary. Both the chemical and the optical mineralogists have constantly, of late, found occasion to separate species which had been united, and to bring together those which had been divided. Everything shows that, in this science, we have our classification still to begin. The detection of that fixity of characters, on which a right establishment of species must rest, is not yet complete, great as the progress is which we have made, by acquiring a knowledge of the laws of crystallization and of {351} definite chemical constitution. Our ignorance may surprise us; but it may diminish our surprise to recollect, that the knowledge which we seek is that of the laws of the physical constitution of all bodies whatever; for to us, as mineralogists, all chemical compounds are minerals.

[Note 51\15: Jahres Bericht. viii. 188.]

The defect of the principle of the natural-history classifiers may be thus stated:--in studying the external characters of bodies, they take for granted that they can, without any other light, discover the relative value and importance of those characters. The grouping of Species into a Genus, of Genera into an Order, according to the method of this school, proceeds by no definite rules, but by a latent talent of appreciation,--a sort of classifying instinct. But this course cannot reasonably be expected to lead to scientific truth; for it can hardly be hoped, by any one who looks at the general course of science, that we shall discover the relation between external characters and chemical composition, otherwise than by tracing their association in cases where both are known. It is urged that in other classificatory sciences, in botany, for example, we obtain a natural classification from external characters without having recourse to any other source of knowledge. But this is not true in the sense here meant. In framing a natural system of botany, we have constantly before our eyes the principles of physiology; and we estimate the value of the characters of a plant by their bearing on its functions,--by their place in its organization. In an unorganic body, the chemical constitution is the law of its being; and we shall never succeed in framing a science of such bodies but by studiously directing our efforts to the interpretation of that law.

On these grounds, then, I conceive, that the bold attempts of Mohs and of Berzelius to give new forms to mineralogy, cannot be deemed successful in the manner in which their authors aspired to succeed. Neither of them can be marked as a permanent reformation of the science. I shall not inquire how far they have been accepted by men of science, for I conceive that their greatest effect has been to point out improvements which might be made in mineralogy without going the whole length either of the pure chemical, or of the pure natural-history system.

Sect. 4.--Return to Mixed Systems with Improvements.

IN spite of the efforts of the purists, mineralogists returned to mixed systems of classification; but these systems are much better than they were before such efforts were made. {352}

The Second System of Berzelius, though not tenable in its rigorous form, approaches far nearer than any previous system to a complete character, bringing together like substances in a large portion of its extent. The System of Mohs also, whether or not unconsciously swayed by chemical doctrines, forms orders which have a community of chemical character; thus, the minerals of the order Haloide are salts of oxides, and those of the order Pyrites are sulphurets of metals. Thus the two methods appear to be converging to a common centre; and though we are unable to follow either of them to this point of union, we may learn from both in what direction we are to look for it. If we regard the best of the pure systems hitherto devised as indications of the nature of that system, perfect both as a chemical and as a natural-history system, to which a more complete condition of mineralogical knowledge may lead us, we may obtain, even at present, a tolerably good approximation to a complete classification; and such a one, if we recollect that it must be imperfect, and is to be held as provisional only, may be of no small value and use to us.

The best of the mixed systems produced by this compromise again comes from Freiberg, and was published by Professor Naumann in 1828. Most of his orders have both a chemical character and great external resemblances. Thus his Haloides, divided into Unmetallic and Metallic, and these again into Hydrous and Anhydrous, give good natural groups. The most difficult minerals to arrange in all systems are the siliceous ones. These M. Naumann calls Silicides, and subdivides them into Metallic, Unmetallic, and Amphoteric or mixed; and again, into Hydrous and Anhydrous. Such a system is at least a good basis for future researches; and this is, as we have said, all that we can at present hope for. And when we recollect that the natural-history principle of classification has begun, as we have already seen, to make its appearance in our treatises of chemistry, we cannot doubt that some progress is making towards the object which I have pointed out. But we know not yet how far we are from the end. The combination of chemical, crystallographical, physical and optical properties into some lofty generalization, is probably a triumph reserved for future and distant years.

Conclusion.--The history of Mineralogy, both in its successes and by its failures, teaches us this lesson;--that in the sciences of classification, the establishment of the fixity of characters, and the discovery of such characters as are fixed, are steps of the first importance in the progress of these sciences. The recollection of this maxim may aid us in {353} shaping our course through the history of other sciences of this kind; in which, from the extent of the subject, and the mass of literature belonging to it, we might at first almost despair of casting the history into distinct epochs and periods. To the most prominent of such sciences, Botany, I now proceed.

{{355}} BOOK XVI.

CLASSIFICATORY SCIENCES.

HISTORY OF SYSTEMATIC BOTANY AND ZOOLOGY.

. . . . . Vatem aspicies quæ rupe sub altâ Fata canit, foliisque notas et nomina mandat. Quæcunque in foliis descripsit carmina virgo Digerit in numerum atque antro seclusa relinquit Illa manent immorta locis neque ab ordine cedunt. VIRGIL. Æn. iii. 443.

Behold the Sibyl!--Her who weaves a long, A tangled, full, yet sweetly flowing song. Wondrous her skill; for leaf on leaf she frames Unerring symbols and enduring names; And as her nicely measured line she binds, For leaf on leaf a fitting place she finds; Their place once found, no more the leaves depart, But fixed rest:--such is her magic art.

{{357}} INTRODUCTION.

WE now arrive at that study which offers the most copious and complete example of the sciences of classification, I mean Botany. And in this case, we have before us a branch of knowledge of which we may say, more properly than of any of the sciences which we have reviewed since Astronomy, that it has been constantly advancing, more or less rapidly, from the infancy of the human race to the present day. One of the reasons of this resemblance in the fortunes of two studies so widely dissimilar, is to be found in a simplicity of principle which they have in common; the ideas of Likeness and Difference, on which the knowledge of plants depends, are, like the ideas of Space and Time, which are the foundation of astronomy, readily apprehended with clearness and precision, even without any peculiar culture of the intellect. But another reason why, in the history of Botany, as in that of Astronomy, the progress of knowledge forms an unbroken line from the earliest times, is precisely the great difference of the kind of knowledge which has been attained in the two cases. In Astronomy, the discovery of general truths began at an early period of civilization; in Botany, it has hardly yet begun; and thus, in each of these departments of study, the lore of the ancient is homogeneous with that of the modern times, though in the one case it is science, in the other, the absence of science, which pervades all ages. The resemblance of the form of their history arises from the diversity of their materials.

I shall not here dwell further upon this subject, but proceed to trace rapidly the progress of Systematic Botany, as the classificatory science is usually denominated, when it is requisite to distinguish between that and Physiological Botany. My own imperfect acquaintance with this study admonishes me not to venture into its details, further than my purpose absolutely requires. I trust that, by taking my views principally from writers who are generally allowed to possess the best insight into the science, I may be able to draw the larger features of its history with tolerable correctness; and if I succeed in this, I shall attain an object of great importance in my general scheme. {358}

I. IMAGINARY KNOWLEDGE OF PLANTS

THE apprehension of such differences and resemblances as those by which we group together and discriminate the various kinds of plants and animals, and the appropriation of words to mark and convey the resulting notions, must be presupposed, as essential to the very beginning of human knowledge. In whatever manner we imagine man to be placed on the earth by his Creator, these processes must be conceived to be, as our Scriptures represent them, contemporaneous with the first exertion of reason, and the first use of speech. If we were to indulge ourselves in framing a hypothetical account of the origin of language, we should probably assume as the first-formed words, those which depend on the visible likeness or unlikeness of objects; and should arrange as of subsequent formation, those terms which imply, in the mind, acts of wider combination and higher abstraction. At any rate, it is certain that the names of the kinds of vegetables and animals are very abundant even in the most uncivilized stages of man's career. Thus we are informed[1\16] that the inhabitants of New Zealand have a distinct name of every tree and plant in their island, of which there are six or seven hundred or more different kinds. In the accounts of the rudest tribes, in the earliest legends, poetry, and literature of nations, pines and oaks, roses and violets, the olive and the vine, and the thousand other productions of the earth, have a place, and are spoken of in a manner which assumes, that in such kinds of natural objects, permanent and infallible distinctions had been observed and universally recognized.

[Note 1\16: Yate's New Zealand, p. 238.]

For a long period, it was not suspected that any ambiguity or confusion could arise from the use of such terms; and when such inconveniences did occur, (as even in early times they did,) men were far from divining that the proper remedy was the construction of a science of classification. The loose and insecure terms of the language of common life retained their place in botany, long after their {359} defects were severely felt: for instance, the vague and unscientific distinction of vegetables into trees, shrubs, and herbs, kept its ground till the time of Linnæus.

While it was thus imagined that the identification of a plant, by means of its name, might properly be trusted to the common uncultured faculties of the mind, and to what we may call the instinct of language, all the attention and study which were bestowed on such objects, were naturally employed in learning and thinking upon such circumstances respecting them as were supplied by any of the common channels through which knowledge and opinion flow into men's minds.

The reader need hardly be reminded that in the earlier periods of man's mental culture, he acquires those opinions on which he loves to dwell, not by the exercise of observation subordinate to reason; but, far more, by his fancy and his emotions, his love of the marvellous, his hopes and fears. It cannot surprise us, therefore, that the earliest lore concerning plants which we discover in the records of the past, consists of mythological legends, marvellous relations, and extraordinary medicinal qualities. To the lively fancy of the Greeks, the Narcissus, which bends its head over the stream, was originally a youth who in such an attitude became enamored of his own beauty: the hyacinth,[2\16] on whose petals the notes of grief were traced (A I, A I), recorded the sorrow of Apollo for the death of his favorite Hyacinthus: the beautiful lotus of India,[3\16] which floats with its splendid flower on the surface of the water, is the chosen seat of the goddess Lackshmi, the daughter of Ocean.[4\16] In Egypt, too,[5\16] Osiris swam on a lotus-leaf and Harpocrates was cradled in one. The lotus-eaters of Homer lost immediately their love of home. Every one knows how easy it would be to accumulate such tales of wonder or religion.

[Note 2\16: Lilium martagon. Ipse suos gemitus foliis inscribit et A I, A I, Flos habet inscriptum funestaque litera ducta est.--OVID.]

[Note 3\16: Nelumbium speciosum.]

[Note 4\16: Sprengel, Geschichte der Botanik, i. 27.]

[Note 5\16: Ib. i. 28.]

Those who attended to the effects of plants, might discover in them some medicinal properties, and might easily imagine more; and when the love of the marvellous was added to the hope of health, it is easy to believe that men would be very credulous. We need not dwell upon the examples of this. In Pliny's Introduction to that book of his {360} Natural History which treats of the medicinal virtues of plants, he says,[6\16] "Antiquity was so much struck with the properties of herbs, that it affirmed things incredible. Xanthus, the historian, says, that a man killed by a dragon, will be restored to life by an herb which he calls balin; and that Thylo, when killed by a dragon, was recovered by the same plant. Democritus asserted, and Theophrastus believed, that there was an herb, at the touch of which, the wedge which the woodman had driven into a tree would leap out again. Though we cannot credit these stories, most persons believe that almost anything might be effected by means of herbs, if their virtues were fully known." How far from a reasonable estimate of the reality of such virtues were the persons who entertained this belief we may judge from the many superstitious observances which they associated with the gathering and using of medicinal plants. Theophrastus speaks of these;[7\16] "The drug-sellers and the rhizotomists (root-cutters) tell us," he says, "some things which may be true, but other things which are merely solemn quackery;[8\16] thus they direct us to gather some plants, standing from the wind, and with our bodies anointed; some by night, some by day, some before the sun falls on them. So far there may be something in their rules. But others are too fantastical and far fetched. It is, perhaps, not absurd to use a prayer in plucking a plant; but they go further than this. We are to draw a sword three times round the mandragora, and to cut it looking to the west: again, to dance round it, and to use obscene language, as they say those who sow cumin should utter blasphemies. Again, we are to draw a line round the black hellebore, standing to the east and praying; and to avoid an eagle either on the right or on the left; for, say they, 'if an eagle be near, the cutter will die in a year.'"

[Note 6\16: Lib. xxv. 5.]

[Note 7\16: De Plantis, ix. 9.]

[Note 8\16: Ἐπιτραγῳδοῦντες.]

This extract may serve to show the extent to which these imaginations were prevalent, and the manner in which they were looked upon by Theophrastus, our first great botanical author. And we may now consider that we have given sufficient attention to these fables and superstitions, which have no place in the history of the progress of real knowledge, except to show the strange chaos of wild fancies and legends out of which it had to emerge. We proceed to trace the history of the knowledge of plants. {361}

II. UNSYSTEMATIC KNOWLEDGE OF PLANTS

A STEP was made towards the formation of the Science of Plants, although undoubtedly a slight one, as soon as men began to collect information concerning them and their properties, from a love and reverence for knowledge, independent of the passion for the marvellous and the impulse of practical utility. This step was very early made. The "wisdom" of Solomon, and the admiration which was bestowed upon it, prove, even at that period, such a working of the speculative faculty: and we are told, that among other evidences of his being "wiser than all men," "he spake of trees, from the cedar-tree that is in Lebanon even unto the hyssop that springeth out of the wall."[9\16] The father of history, Herodotus, shows us that a taste for natural history had, in his time, found a place in the minds of the Greeks. In speaking of the luxuriant vegetation of the Babylonian plain,[10\16] he is so far from desiring to astonish merely, that he says, "the blades of wheat and barley are full four fingers wide; but as to the size of the trees which grow from millet and sesame, though I could mention it, I will not; knowing well that those who have not been in that country will hardly believe what I have said already." He then proceeds to describe some remarkable circumstances respecting the fertilization of the date-palms in Assyria.

[Note 9\16: 1 Kings iv. 33.]

[Note 10\16: Herod. i. 193.]

This curious and active spirit of the Greeks led rapidly, as we have seen in other instances, to attempts at collecting and systematizing knowledge on almost every subject: and in this, as in almost every other department, Aristotle may be fixed upon, as the representative of the highest stage of knowledge and system which they ever attained. The vegetable kingdom, like every other province of nature, was one of the fields of the labors of this universal philosopher. But though his other works on natural history have come down to us, and are a most valuable monument of the state of such knowledge in his time, his Treatise on Plants is lost. The book De Plantis {362} which appears with his name, is an imposture of the middle ages, full of errors and absurdities.[11\16]

[Note 11\16: Mirbel, Botanique, ii. 505.]

His disciple, friend, and successor, Theophrastus of Eresos, is, as we have said already, the first great writer on botany whose works we possess; and, as may be said in most cases of the first great writer, he offers to us a richer store of genuine knowledge and good sense than all his successors. But we find in him that the Greeks of his time, who aspired, as we have said, to collect and systematize a body of information on every subject, failed in one half of their object, as far as related to the vegetable world. Their attempts at a systematic distribution of plants were altogether futile. Although Aristotle's divisions of the animal kingdom are, even at this day, looked upon with admiration by the best naturalists, the arrangements and comparisons of plants which were contrived by Theophrastus and his successors, have not left the slightest trace in the modern form of the science; and, therefore, according to our plan, are of no importance in our history. And thus we can treat all the miscellaneous information concerning vegetables which was accumulated by the whole of this school of writers, in no other way than as something antecedent to the first progress towards systematic knowledge.

The information thus collected by the unsystematic writers is of various kinds; and relates to the economical and medicinal uses of plants, their habits, mode of cultivation, and many other circumstances: it frequently includes some description; but this is always extremely imperfect, because the essential conditions of description had not been discovered. Of works composed of materials so heterogeneous, it can be of little use to produce specimens; but I may quote a few words from Theophrastus, which may serve to connect him with the future history of the science, as bearing upon one of the many problems respecting the identification of ancient and modern plants. It has been made a question whether the following description does not refer to the potato.[12\16] He is speaking of the differences of roots: "Some roots," he says, "are still different from those which have been described; as that of the arachidna[13\16] plant: for this bears fruit underground as well as above: the fleshy part sends one thick root deep into the ground, but the others, which bear the fruit, are more slender {363} and higher up, and ramified. It loves a sandy soil, and has no leaf whatever."

[Note 12\16: Theoph. i. 11.]

[Note 13\16: Most probably the Arachnis hypogæa, or ground-nut.]

The books of Aristotle and Theophrastus soon took the place of the Book of Nature in the attention of the degenerate philosophers who succeeded them. A story is told by Strabo[14\16] concerning the fate of the works of these great naturalists. In the case of the wars and changes which occurred among the successors of Alexander, the heirs of Theophrastus tried to secure to themselves his books, and those of his master, by burying them in the ground. There the manuscripts suffered much from damp and worms; till Apollonicon, a book-collector of those days, purchased them, and attempted, in his own way, to supply what time had obliterated. When Sylla marched the Roman troops into Athens, he took possession of the library of Apollonicon; and the works which it contained were soon circulated among the learned of Rome and Alexandria, who were thus enabled to Aristotelize[15\16] on botany as on other subjects.

[Note 14\16: Strabo, lib. xiii. c. i. § 54.]

[Note 15\16: Ἀριστοτλίζειν.]

The library collected by the Attalic kings of Pergamus, and the Alexandrian Museum, founded and supported by the Ptolemies of Egypt, rather fostered the commentatorial spirit than promoted the increase of any real knowledge of nature. The Romans, in this as in other subjects, were practical, not speculative. They had, in the times of their national vigor, several writers on agriculture, who were highly esteemed; but no author, till we come to Pliny, who dwells on the mere knowledge of plants. And even in Pliny, it is easy to perceive that we have before us a writer who extracted his information principally from books. This remarkable man,[16\16] in the middle of a public and active life, of campaigns and voyages, contrived to accumulate, by reading and study, an extraordinary store of knowledge of all kinds. So unwilling was he to have his reading and note-making interrupted, that, even before day-break in winter, and from his litter as he travelled, he was wont to dictate to his amanuensis, who was obliged to preserve his hand from the numbness which the cold occasioned, by the use of gloves.[17\16]

[Note 16\16: Sprengel, i. 163.]

[Note 17\16: Plin. Jun. Epist. 3, 5.]

It has been ingeniously observed, that we may find traces in the botanical part of his Natural History, of the errors which this hurried and broken habit of study produced; and that he appears frequently to have had books read to him and to have heard them amiss.[18\16] Thus, {364} among several other instances, Theophrastus having said that the plane-tree is in Italy rare,[19\16] Pliny, misled by the similarity of the Greek word (spanian, rare), says that the tree occurs in Italy and Spain.[20\16] His work has, with great propriety, been called the Encyclopædia of Antiquity; and, in truth, there are few portions of the learning of the times to which it does not refer. Of the thirty-seven Books of which it consists, no less than sixteen (from the twelfth to the twenty-seventh) relate to plants. The information which is collected in these books, is of the most miscellaneous kind; and the author admits, with little distinction, truth and error, useful knowledge and absurd fables. The declamatory style, and the comprehensive and lofty tone of thought which we have already spoken of as characteristic of the Roman writers, are peculiarly observable in him. The manner of his death is well known: it was occasioned by the eruption of Vesuvius, A.D. 79, to which, in his curiosity, he ventured so near as to be suffocated.

[Note 18\16: Sprengel, i. 163.]

[Note 19\16: Theoph. iv. 7. Ἔν μὲν γὰρ τῷ Ἀδρίᾳ πλάτανον οὐ φασὶν εἶναι πλῆν περὶ το Διομήδους ἱερόν, σπανίαν δὲ καὶ ἐν Ἰταλίᾳ πάσῃ]

[Note 20\16: Plin. Nat. Hist. xii. 3. Et alias (platanos) fuisse in Italia, ac nominatim Hispania, apud auctores invenitur.]

Pliny's work acquired an almost unlimited authority, as one of the standards of botanical knowledge, in the middle ages; but even more than his, that of his contemporary, Pedanius Dioscorides, of Anazarbus in Cilicia. This work, written in Greek, is held by the best judges[21\16] to offer no evidence that the author observed for himself. Yet he says expressly in his Preface, that his love of natural history, and his military life, have led him into many countries, in which he has had opportunity to become acquainted with the nature of herbs and trees.[22\16] He speaks of six hundred plants, but often indicates only their names and properties, giving no description by which they can be identified. The main cause of his great reputation in subsequent times was, that he says much of the medicinal virtues of vegetables.

[Note 21\16: Mirbel, 510.]

[Note 22\16: Sprengel, i. 136.]

We come now to the ages of darkness and lethargy, when the habit of original thought seems to die away, as the talent of original observation had done before. Commentators and mystics succeed to the philosophical naturalists of better times. And though a new race, altogether distinct in blood and character from the Greek, appropriates to itself the stores of Grecian learning, this movement does not, as might be expected, break the chains of literary slavery. The Arabs {365} bring, to the cultivation of the science of the Greeks, their own oriental habit of submission, their oriental love of wonder; and thus, while they swell the herd of commentators and mystics, they produce no philosopher.

Yet the Arabs discharged an important function in the history of human knowledge,[23\16] by preserving, and transmitting to more enlightened times, the intellectual treasures of antiquity. The unhappy dissensions which took place in the Christian church had scattered these treasures over the East, at a period much antecedent to the rise of the Saracen power. In the fifth century, the adherents of Nestorius, bishop of Constantinople, were declared heretical by the Council of Ephesus (A.D. 431), and driven into exile. In this manner, many of the most learned and ingenious men of the Christian world were removed to the Euphrates, where they formed the Chaldean church, erected the celebrated Nestorian school of Edessa, and gave rise to many offsets from this in various regions. Already, in the fifth century, Hibas, Cumas, and Probus, translated the writings of Aristotle into Syriac. But the learned Nestorians paid an especial attention to the art of medicine, and were the most zealous students of the works of the Greek physicians. At Djondisabor, in Khusistan, they became an ostensible medical school, who distributed academical honors as the result of public disputations. The califs of Bagdad heard of the fame and the wisdom of the doctors of Djondisabor, summoned some of them to Bagdad, and took measures for the foundation of a school of learning in that city. The value of the skill, the learning, and the virtues of the Nestorians, was so strongly felt, that they were allowed by the Mohammedans the free exercise of the Christian religion, and intrusted with the conduct of the studies of those of the Moslemin, whose education was most cared for. The affinity of the Syriac and Arabic languages made the task of instruction more easy. The Nestorians translated the works of the ancients out of the former into the latter language: hence there are still found Arabic manuscripts of Dioscorides, with Syriac words in the margin. Pliny and Aristotle likewise assumed an Arabic dress; and were, as well as Dioscorides, the foundation of instruction in all the Arabian academies; of which a great number were established throughout the Saracen empire, from Bokhara in the remotest east, to Marocco and Cordova in the west. After some time, the Mohammedans themselves began to translate and {366} extract from their Syriac sources; and at length to write works of their own. And thus arose vast libraries, such as that of Cordova, which contained 250,000 volumes.

[Note 23\16: Sprengel, i. 203.]

The Nestorians are stated[24\16] to have first established among the Arabs those collections of medicinal substances (Apothecæ), from which our term Apothecary is taken; and to have written books (Dispensatoria) containing systematic instructions for the employment of these medicaments; a word which long continued to be implied in the same sense, and which we also retain, though in a modified application (Dispensary).

[Note 24\16: Sprengel, i. 205.]

The directors of these collections were supposed to be intimately acquainted with plants; and yet, in truth, the knowledge of plants owed but little to them; for the Arabic Dioscorides was the source and standard of their knowledge. The flourishing commerce of the Arabians, their numerous and distant journeys, made them, no doubt, practically acquainted with the productions of lands unknown to the Greeks and Romans. Their Nestorian teachers had established Christianity even as far as China and Malabar; and their travellers mention[25\16] the camphor of Sumatra, the aloe-wood of Socotra near Java, the tea of China. But they never learned the art of converting their practical into speculative knowledge. They treat of plants only in so far as their use in medicine is concerned,[26\16] and followed Dioscorides in the description, and even in the order of the plants, except when they arrange them according to the Arabic alphabet. With little clearness of view, they often mistake what they read:[27\16] thus when Dioscorides says that ligusticon grows on the Apennine, a mountain not far from the Alps; Avicenna, misled by a resemblance of the Arabic letters, quotes him as saying that the plant grows on Akabis, a mountain near Egypt.

[Note 25\16: Sprengel, i. 206.]

[Note 26\16: Ib. i. 207.]

[Note 27\16: Ib. i. 211.]

It is of little use to enumerate such writers. One of the most noted of them was Mesuë, physician of the Calif of Kahirah. His work, which was translated into Latin at a later period, was entitled, On Simple Medicines; a title which was common to many medical treatises, from the time of Galen in the second century. Indeed, of this opposition of simple and compound medicines, we still have traces in our language: {367} He would ope his leathern scrip, And show me simples of a thousand names, Telling their strange and vigorous faculties. MILTON, Comus.

Where the subject of our history is so entirely at a stand, it is unprofitable to dwell on a list of names. The Arabians, small as their science was, were able to instruct the Christians. Their writings were translated by learned Europeans, for instance Michael Scot, and Constantine of Africa, a Carthaginian who had lived forty years among the Saracens[28\16] and who died A.D. 1087. Among his works, is a Treatise, De Gradibus, which contains the Arabian medicinal lore. In the thirteenth century occur Encyclopædias, as that of Albertus Magnus, and of Vincent of Beauvais; but these contain no natural history except traditions and fables. Even the ancient writers were altogether perverted and disfigured. The Dioscorides of the middle ages varied materially from ours.[29\16] Monks, merchants, and adventurers travelled far, but knowledge was little increased. Simon of Genoa,[30\16] a writer on plants in the fourteenth century, boasts that he perambulated the East in order to collect plants. "Yet in his Clavis Sanationis," says a modern botanical writer,[31\16] "we discover no trace of an acquaintance with nature. He merely compares the Greek, Arabic, and Latin names of plants, and gives their medicinal effect after his predecessors:"--so little true is it, that the use of the senses alone necessarily leads to real knowledge.

[Note 28\16: Sprengel, i. 230.]

[Note 29\16: Ib. i. 239.]

[Note 30\16: Ib. i. 241.]

[Note 31\16: Ib. ib.]

Though the growing activity of thought in Europe, and the revived acquaintance with the authors of Greece in their genuine form, were gradually dispelling the intellectual clouds of the middle ages, yet during the fifteenth century, botany makes no approach to a scientific form. The greater part of the literature of this subject consisted of Herbals, all of which were formed on the same plan, and appeared under titles such as Hortus, or Ortus Sanitatis. There are, for example, three[32\16] such German Herbals, with woodcuts, which date about 1490. But an important peculiarity in these works is that they contain some indigenous species placed side by side with the old ones. In 1516, The Grete Herbal was published in England, also with woodcuts. It contains an account of more than four hundred vegetables, and their {368} products; of which one hundred and fifty are English, and are no way distinguished from the exotics by the mode in which they are inserted in the work.

[Note 32\16: Augsburg, 1488. Mainz, 1491. Lubec, 1492.]

We shall see, in the next chapter, that when the intellect of Europe began really to apply itself to the observation of nature, the progress towards genuine science soon began to be visible, in this as in other subjects; but before this tendency could operate freely, the history of botany was destined to show, in another instance, how much more grateful to man, even when roused to intelligence and activity, is the study of tradition than the study of nature. When the scholars of Europe had become acquainted with the genuine works of the ancients in the original languages, the pleasure and admiration which they felt, led them to the most zealous endeavors to illustrate and apply what they read. They fell into the error of supposing that the plants described by Theophrastus, Dioscorides, Pliny, must be those which grew in their own fields. And thus Ruellius,[33\16] a French physician, who only travelled in the environs of Paris and Picardy, imagined that he found there the plants of Italy and Greece. The originators of genuine botany in Germany, Brunfels and Tragus (Bock), committed the same mistake; and hence arose the misapplication of classical names to many genera. The labors of many other learned men took the same direction, of treating the ancient writers as if they alone were the sources of knowledge and truth.

[Note 33\16: De Natura Stirpium, 1536.]

But the philosophical spirit of Europe was already too vigorous to allow this superstitious erudition to exercise a lasting sway. Leonicenus, who taught at Ferrara till he was almost a hundred years old, and died in 1524,[34\16] disputed, with great freedom, the authority of the Arabian writers, and even of Pliny. He saw, and showed by many examples, how little Pliny himself knew of nature, and how many errors he had made or transmitted. The same independence of thought with regard to other ancient writers, was manifested by other scholars. Yet the power of ancient authority melted away but gradually. Thus Antonius Brassavola, who established on the banks of the Po the first botanical garden of modern times, published in 1536, his Examen omnium Simplicium Medicamentorum; and, as Cuvier says,[35\16] though he studied plants in nature, his book (written in the {369} Platonic form of dialogue), has still the character of a commentary on the ancients.

[Note 34\16: Sprengel, i. 252.]

[Note 35\16: Hist. des Sc. Nat. partie ii. 169.]

The Germans appear to have been the first to liberate themselves from this thraldom, and to publish works founded mainly on actual observation. The first of the botanists who had this great merit is Otho Brunfels of Mentz, whose work, Herbarum Vivæ Icones, appeared in 1530. It consists of two volumes in folio, with wood-cuts; and in 1532, a German edition was published. The plants which it contains are given without any arrangement, and thus he belongs to the period of unsystematic knowledge. Yet the progress towards the formation of a system manifested itself so immediately in the series of German botanists to which he belongs, that we might with almost equal propriety transfer him to the history of that progress; to which we now proceed.