great man's history, that sort of detail which originates in singular or various adventures. To know at once how to enlighten his cotemporaries and to be esteemed by them; to possess talents, and yet be respected by criticism; to be rich and possess family honours without exciting envy; to preserve his health and mental powers after long-continued and indefatigable labours; are a combination of advantages which so seldom occur in the life of man, that we cannot but feel interested in knowing the par ticulars of these advantages, and in studying the causes which produced them. Mr. Cavendish was born in London on the 10th of October, 1731. His father was Lord Charles Cavendish, likewise a Member of the Royal Society, and Trustee of the British Mu seum. llis family, which traces its descent from one of the companions of William the Conqueror, is amongst the most illustrious houses of Great Britain. It has, for more than two centuries, belonged to the peerage, and William III, in 1694, exalted its head to the title of Duke of Devonshire. It has been observed that in England there are more people of quality who se riously apply themselves to the sciences, or to letters, than in other countries. The fact is, that, from the nature of the government, neither birth nor fortune can confer distinction upon the possessors, unless these are accompanied by talents. Hence, it is necessary to prepare the young nobility for acquiring general knowledge, by a proper course of studies; and, amongst so many young men who have the advantages of a scientific education, some are always found who rather choose to employ their faculties in searching for imperishable facts, than in merely supporting the vacillating inte rests of the hour. The whole life of Mr. Cavendish is a proof that such a preference was implanted in his very nature: but domestic example was necessary to confirm, at an early period, this inclination. Lord Charles, his father, was also a lover of the sciences, and has left some good observations on natural philosophy. It is probable that he directed the early studies of his son; but we have no account of the method he adopted in bis elementary education, nor even of the first attempts of the young Henry in the road of science. He appeared in it suddenly, but nevertheless in such a manner as to indicate that he had been well instructed. At his very commencement in philosophy, he struck into a line before then unknown, and gave the signal for the arrival of an entirely new epoch. We allude to the Dissertation on Air, which he laid before the Royal Society in 1766: an article, the object of winch was nothing less than to establish the fact, till then never heard of; namely, that air is not an element; but that there are several kinds of air essentially different. From the time of VAN HELMONT, philosophers knew that various bodies exhale fluids, which resemble air by their permanent elasticity. BOYLE Soon found out that they cannot serve for respiration; HALES thought they might be measured; and conceived the means of effecting this point. BROWNRIGG and VENEL had shown that certain mineral waters derive from them their pungent taste: BLACK had discovered, that, by their presence, quick-lime is distinguished from lime-stone, as well as are the caustic from the common alkalis. MACBRIDE at length called the attention of physicians towards them, by employing them against putrefaction: but, amidst all these investigations, a sufficient distinction had not been made between the different sorts of airs: it was not generally believed that they were particular substances in their species; and more than one philosopher of renown persisted that they were only common air, altered by the emanations of the bodies which furnished it; though nobody could precisely point out of what these supposed emanations consisted. Mr. Cavendish, however, gave in his paper; and, in a few pages, he threw such light on the subject, that there was no longer but one opinion. He compared, for example, the elastie fluid extracted from lime and the alkalis, with that produced by fermentation and putrefaction, as well as with that which prevails at the bottom of wells, mines, and pits; and he showed that they all possess the same properties, and form only one and the same fluid, for which was afterwards reserved the name of fixed air. He ascertamed the specific gravity of this air, and found it to be always the same, or greater by one-third than that of common air; this fact explained why fixed air always fills low Phil. Trans. 1766. p. 141. ptacos, places, as well as the deleterious effects which it occasions. He discovered that this sort of air has the property of combining with water, and then dissolving lime-stone and iron; which ilJustrates the effects of petrifying waters, of stalactites, and of the presence of iron in mineral waters. In short, he convinced himself that it is precisely this same air which is given out on the combustion of charcoal, and which renders this kind of combustion so dangerous. His experiments on inflammable air were still more novel and interesting. Before the period in question, scarcely any one had given attention to the nature of this fluid, which was known only from the explosions which it sometimes caused in the mines. Mr. Cavendish, however, by treating it like fixed air, proved that inflammable air is identical, and possesses the same properties, whether it be obtained from the solution of iron, or from that of zinc or copper: and amongst these properties, he particularly proved it to possess that specific gravity, or rather rarity, which renders it nearly ten times lighter than common air; and of which peculiar quality our brother-member, M. CHARLES, has since made such a notable application, by rendering aërial travel. ling safe and easy! In short, we may say, that, without the discovery of Mr. CAVENDISH, and the application of it by M. CHARLES, the attempt of M. de MONTGOLFIER Would scarcely have been practicable, so numerous are the dangers and embarrassments of the aeronaut, if he be obliged to keep the common air dilated by means of fire, as must be the case with all the Montgolfier balloons. The labours of Mr. Cavendish respect ing airs had, however, far greater consequences, the importance of which was speedily discovered. The fact, once ascertained, that there might exist several elastic fluids, invariable in their properties, and specifically different in their nature, led to the first investigations of PRIESTLEY, which made known two new kinds of fluids, phlogistic and nitrous air. Soon after this discovery, men began to find out in what way the different airs influenced the phenomena of nature, and to infer, that systems of philosophy and chemistry, established without due regard to such powerful and universal agents, could not be permanent. The minds of philosophers, agitated by impatience and doubts, which formed their pucipal resource, were in a sort of fer mentation, and each person endeavoured to give reasons for supporting those theories which were evidently going to ruin. The introduction of fixed air amongst the acids, by BERGMANN, though it simplified chemistry in a small degree, ap peared but a slight palliative to the ra dical vice which was now admitted. The science had remained in this state for the space of seven years, when LaVOISIER received the first light of his famous doctrine. Having obtained a quantity of fixed air, from the reduction of metals by carbon, he concluded, that the calcination of metallic substances was nothing more than their combination with fixed air. A year afterwards, BAYER reduced calces of mercury without carbon, in luted vessels, and thus sapped the principal foundation of the phlogistic theory. Lavoisier next examined the air produced by these experiments with out carbon, and found it respirable; and nearly about the same time, PRIESTLEY discovered, that this was precisely the part of the atmosphere necessary at once for respiration and combustion. LAVOISIER now made his next step. He asserted, that respiration, the calci nation of metals, and combustion, are similar operations, caused by the combi nations of respirable air; that fixed air is the peculiar product of the combustion of charcoal; but the phenomena of solu tions, and the inflammable air which ap pears on those occasions, were not yet explained. It required six more years to ascertain these points, and Mr. CAVEN DISH had the honour of the discovery. SCHEELE had observed that, on burning inflammable air, he obtained neither fixed air nor phlogisticated air; the whole seemed to disappear. MACQUER, endeavouring to retain the vapour from this combustion, observed, with astonishment, some moisture on the vessels he made use of; but he thought with Scheele, that the airs were lost. Mr. Cavendish, who had in some degree in troduced inflammable air into chemical experiments, was the first to point out the great part which it would act in the science. Acting, as he did, on his first discovery, with precision, on a sube ject vaguely understood before his time, he deflagrated inflammable air in closed vessels, by the electric spark, by supplying gradually as much respirable air as was necessary for the combustion: he then found, that the former of these Philos. Trans. 1784; Part I. P. 119. aus M airs absorbed a certain portion of the latter, and that the whole resolved into a quantity of water, equal to the weight of the two airs that had disappeared. This great phenomenon, which Mr. Cavendish spent three years in confirming, was announced to the Royal Society on the 14th of January, 1781. Our brother member, the Count de PELUSE, who had conceived the same idea, and made the same experiments as Mr. Cavendish, communicated the result about the same time to LAVOISIER and M. de LAPLACE, If the combination of the airs give out water, said M. de Laplace, this must be the result of its decomposition. Philosophers then employed themselves in decomposing water, in the same manner as they had composed it. Lavoisier per. formed the two operations, with great solemnity, before a committee of the Acadermy; and those experiments, having formed the basis of his new theory, threw much light on what had till then escaped notice. In fact, water being nothing but a combination of the two airs, wherever it is found, it will always furnish them by decomposition; and, wherever the airs exist, water can be produced from their combination. Hence, as inflammable air is obtained by metallic solutions, and by a series of other results, the composition of organised beings, and the most complicated changes of their principles are cffected. In short, from this period, the theory of chemistry was placed upon immutable bases. Thus, it may be said, that this new the. ory, which has effected so great a revolution in the sciences, is indebted for its origin to a discovery by Mr. CAVENDISH; and that a second discovery, by the same philosopher, rendered it complete. This gentleman, however, made a third discovery, which would have been sufficient to immortalise him, if the two others had not occurred: it was that of the composition of the nitrous acid, a substance so useful in the arts, and so abundant in nature; a substance about which, before the time of Mr. Cavendish, chemists entertained only vague and bypothetical ideas.* From his first experiments on the combustion of inflammable air, it occurred to him that there was a formation of nitrous acid, and that it would accrue in proportion to the quantity of the air employed, Phil. Trans. 1786. which was then called phlogiston, but which has since been termed azote. On examining afterwards the product from the detonation of nitre by charcoal, he found it to consist of this same phlogisticated air and fixed air. It was the carbon which had given out the latter. Consequently the former could only have been furnished by the acid of the nitre. Mr. Cavendish was soon enabled to prove, by direct experiments, the accuracy of his conjecture. On firing, by the electric spark, a mixture of atmospheric and phlogisticated airs, he con verted it into nitrous air; which, of itself, changes into an acid by a new addition of atmospheric air. Thus the elements of the nitrous 'acid were discovered to be the same as those of the atmosphere, only in different proportions; and from that time we had clear ideas of the universal, and till then incomprehensible, generation of that acid. One cannot peruse without a sort of enthusiasm, the history of this epoch, the most brilliant which ever occurred to chemistry. Discoveries seemed to press upon one another. Mr. Cavendish having communicated the experiment he had just made on the nitric acid to our colleague BERTHOLLET, he received from him, in return, post after post, accounts of the decomposition of ammonia, in ine flammable, as well as in phlogisticated air. For what men, and what an age, was such a correspondence reserved! At length, Mr. Cavendish examined the atmosphere itself; and it produced on living beings such various effects, that it was naturally supposed to be very va riable in the proportion of its elements. Priestley, who had discovered the pure and respirable air, had also discovered the means of ascertaining the quantity of such air in (or the respirability of) any air whatever. It was only necessary to measure the portion of pure air which was absorbed on mixing it with nitrous air; but his instruments were not at that time perfect; notwithstanding the improvements made in them by FONTANA. Mr. Cavendish, by a slight difference in the process of making them, gave them a much greater precision;* and, having employed them in comparing pure air in different places, and at various times, he ascertained a result which was little expected; namely, that the quantity of re * Philos. Trans. 1785, Part I. p. 105. spirable spirable air is every where the same; and that the smells which so sensibly affect our organs, and the miasmata which so dreadfully assail our system, cannot be destroyed by any chemical means; a fact, which, though on the first view it is very discouraging, nevertheless affords to the reflecting mind an immense scope, and exposes, at a vast distance, the sha. dows of sciences which exist not yet for us, but for which alone it is perhaps reserved to explain to us the hidden secrets of those which already prevail. M. DE HUMBOLDT has confirmed this fact in the most distant regions, by means of the eudiometer of inflammable air; and M. GAY LUSSAC, on ascending in a balloon, found it equally true at the greatest heights which man could reach, as it was in the inferior strata of the atmosphere. Thus these courageous philosophers always made use of an agent found out by Mr. Cavendish, to verify another of his discoveries. Such are the circumstances which have justly given Mr. Cavendish a place amongst chemists. They occupy, in de scription, but a very few pages of print; but they will outlive many a large volume: the labour, however, which they once cost, must not be estimated by the space which they now fill. To untie the concealed knot which unites so many complicated phenomena; to pursue the same principles, amidst so many alterations and metamorphoses, aud particularly to expose so clearly what had for so many centuries escaped the mest able of men, and to make these facts evident to all the world, could only be the effect of the most persevering and well-directed cogitations. Mr. Cavendish, indeed, was a living proof of the truth of the adage of one of his most il lustrious cotemporaries--that genius is only an additional incitement to patience; which is strictly true, when we allude to the patience of a man of intellect. Another qualification equally laudable, was this gentleman's rigid system of experiments. No sophistry, nothing of a doubtful nature, was suttered to pass unelucidated. His perseverance was so well known, that his cotemporaries took pleasure in submitting to him the results of their inquiries; being almost certain, that, if he approved of them, nobody else could amend them. He was, however, more severe with himself, in matters of science, than he was towards any other person; and it was this rigid plan which gave to his labours such a degree of per fection, that, even at the present day, nothing can be added to, or abstracted from them; although his first reports were. pablished more than forty years ago, and the science to which they relate has undergone, in the interval, a complete revolution; an advantage which perhaps no other man has possessed since writ ings on the sciences first became general. This rigorous spirit of investigation, introduced into chemistry through the influence of Mr. Cavendish, has rendered 23 eminent services to this science as his discoveries themselves; for it is to his system that we are indebted, in a great degree, for those discoveries which he did not make. About the middle of the eighteenth century chemistry seemed to be the only asylum for the systems and suppositions which Newton had driven from philoso phy. Cavendish and Bergmann expelled them from this last resort, and cleansed this Augean stable from the filth of the Hermetic philosophy. After them o body dared to operate otherwise than with determinate quantities, and by keeping an exact account of all kinds of products! It is this mode of proceeding which forms the distinguishing characte ristic of modern chemistry, much more so than its theories, which, however fine they may appear to us, would not per haps be invulnerable if we were at some future time to succeed in obtaining substances which at present are unknown to us. The persevering or rigid spirit of Mr. Cavendish was owing to a profound study of geometry, of which he likewise made direct applications, and sometimes with as much success as his researches in chemistry. Such, in particular, is his determination of the mon density, or, what is the same thing, of the total weight of the globe; an idea which has at first something in it that is terrific, but which is nevertheless reduced to a simple mechanical problem. Archimedes only wanted a point of support to enable him to move the carth, but this was not necessary to enable Mr. Cavendish to weigh it! Mr. MITCHELL, another Member of the Royal Society, who died some time ago, had conceived the means of performing this experiment, and had constructed an apparatus, which was nearly the same as * Phil, Trans, 1798. Part II. p. 469. Our our late colleague, M. COULOMB, had already employed, for measuring the power of electricity and that of the load-stone. A lever six feet long, and having at its extremities a little leaden ball, was suspended horizontally by the middle to a vertical thread. When the lever had attained an equilibrium, and become stationary, there was brought towards each of its ends a great mass of lead, of a given weight and diameter: the attraction of the masses on the balls put the lever in motion, the thread then twisted, in order to yield to this action, and stretching, to return to its former state, it inade the lever describe little horizontal ares, as the ordinary weight: that is to say, the traction of the earth causes vertical aroo be described by the pendulum; and, on comparing the extent and duration of these oscillations with those of the pendulum, we obtain the produce of their causes, that is, of the attractive power of the masses of lead, and of that of the whole terrestrial globe. But we can only give a rough sketch of the apparatus, and of the cautions and calculations which the experiment required. The moveable power of the lever was such, that the least difference of heat be tween the two balls, or only between the different parts of the air, occasioned a current that was sufficient to make it vibrate. It was even necessary to find the degree of attraction of the sides of the wooden box in which it was contained and the care in measuring the extent of to observe the vibrations, and even them without altering them by approach All ing too near, was inconceivable. these difficulties did not occur till the performance of the experiments, and the delicate means which were used to overcome them, the necessity of which had not been foreseen, even by Mr. Mitchell, belong entirely to Mr. Cavendish. The result was singular. The mean density of the globe must be almost five times and a half greater than that of water. From this discovery it results, that not only the globe has no vacuum, but that the substances in its interior must be heavier than those on its surface; for the stones of which common rocks consist are not more than about three, or seldom four, times heavier than water; and no known stone is five times as heavy. We may therefore believe that metals abound most towards the centre of the globe. Thus has this simple experiment given entirely new ideas respecting the theory of the earth. 1 At first this discovery appeared to contradict that of MASKELYNE, in which the deviation produced by the vicinity of a mountain, on the plumb line of his instruments, had made him conclude, that the mean density of the globe was only four times and a half greater than that of water. But it is asserted that, these experiments having been since made with more accuracy, their result comes much nearer to that of Mr. Cavendish. This gentleman was also one of the first who applied calculation to the theory of electricity. He performed this task before the appearance of the work of pinus, but the account of it was not printed till afterwards. It is founded on the same hypothesis; that is to say, on one single electric substance, the particles of which mutually repelled each other, and would be attracted by other bodies. But Mr. Cavendish went further than pinus, by supposing that, if this action is exerted in a less degree than the inverse of the cube from the distance, we n ay prove, by means of the theorem of Newton, on the attraction of a sphere, that all the electric matter of a body of this form must be on its surface.* It is known that our colleague, the late M. Coulomb, has since shown, by direct experiments, that the action of electricity is exerted in the inverse ratio of the square of the distance; and he has proved in a much more general manner, the necessity of this distribution on the surface of bodies, whatever may be their figure. He When WALSH announced the analogy between the shock given by the torpedo, and that of the Leyden phial, it was objected that this first did not produce sparks. Mr. Cavendish, however, set about explaining the difference. constructed, on the principles of his explanation, a kind of artificial torpedo, which presented the same phenomena on being electrified. The real cause of animal electricity, nevertheless, did not occur to him; and it remained for Volta to discover an apparatus for continually producing this wonderful fluid, and in cessantly to electrify of its own accord; an apparatus, very probably, sunilar, in its essential points, to those with which nature has supplied electric fish. It is also known that the same Me Walsh observed sparks emitted from, the electric cel of South America; a fish which possesses this property in a much |