Cavendish, Henry 1731-1810, natural philosopher, was the eldest son of Lord Charles Cavendish, third son of the second Duke of Devonshire by Lady Anne Grey, fourth daughter of Henry, duke of Kent. He was born on 10 Oct. 1731, not in England, as is sometimes stated, but, according to Lord Burlington, at Nice, where his mother had gone on account of ill-health. His mother died when he was about two years old. In 1742 he became a pupil of the Rev. Dr. Newcombe, who was master of the Hackney seminary. On 18 Dec. 1749 Cavendish went directly from school to Cambridge, and entered Peterhouse College. He commenced residence on 24 Nov., and resided very regularly until 23 Feb. 1753, when he left without taking his degree.
     After leaving college, Cavendish appears to have lived chiefly in London, though we find him, accompanied by his brother Frederick, visiting Paris. The obscurity which hangs over Cavendish's private history renders it impossible to determine what induced him to devote himself to the study of experimental science. Mathematics appear, from the numerous unpublished papers which are still in existence, to have been his favourite study. His first recorded scientific work was Experiments on Arsenic, which he carefully wrote out for the instruction of some friends, and which from a date on some memorandums appear to have been the subject of his investigations in 1764. In Cavendish's Note-book of Experiments we find notices of an extensive series of experiments on heat bearing the date of 5 Feb. 1765, which were never publicly referred to until 1783. These researches were remarkable from being made when the doctrine of phlogiston was generally adopted, and had they been published they would have given Cavendish chronological precedence to Black. Cavendish certainly investigated the evolution of heat which attends the solidification of liquids and the condensation of gases. He also constructed tables of the specific heats of various bodies, being at this time evidently ignorant of the labours of Black in that direction. In 1766 Cavendish made his first public contribution to science by sending to the Royal Society a paper on Factitious Airs. Three parts only of this memoir were published. In 1767 we find in the Philosophical Transactions a communication from Cavendish, being the Analysis of one of the London Pump-waters (that of Rathbone Place). In this he noticed the large quantity of calcareous earth which was deposited on boiling, which he proved was retained in solution by carbonic acid. Finding that other London pump-waters gave a precipitate of calcareous earth with lime water, and yielded a similar residue by evaporation, Cavendish thought it reasonable to conclude that the unneutralised earth in all waters is suspended merely by being united to more than its natural proportion of fixed air (ie. carbonic acid). Cavendish was prepared for this by the investigation of Dr. Brownrigg, who had found that a great deal of fixed air is contained in spa water. Dr. Black also, in his Inaugural Dissertation in 1754, explained to his students at the university of Glasgow the properties of carbonic acid, and exhibited some of its characteristic peculiarities. Cavendish, however, determined the specific gravity of this gas, and was the first to show that a small quantity of it was sufficient to deprive common air of the power of supporting flame or sustaining life. In January 1783 Cavendish read before the Royal Society An Account of a new Eudiometer. During this long interval Bergmann, Scheele, Lavoisier, and Priestley had been actively engaged in endeavouring to determine the composition of the atmosphere. The prevailing hypothesis of chemists at this time was that there existed an hypothetical principle, called phlogiston by Stahl, which accounted for the phenomena of combustion.
     It is evident that this hypothetical phlogiston, or matter of heat, was identical with hydrogen gas, and Priestley called this element inflammable air. Cavendish, in the first part of his paper on Factitious Airs, treats of hydrogen, and some writers have consequently regarded him as the discoverer of that gas. He certainly never claims this himself, and referring to the explosibility of a mixture of air and hydrogen, he says it has been observed by others. Boyle in the seventeenth century mentions this gas as being familiar to many, and Dr. T. Thomson informs us that the combustibility of hydrogen was known about the beginning of the eighteenth century, and was often exhibited as a curiosity, being especially mentioned in Cramer's Elementa Docimasia (1739). Cavendish, with his usual honesty, states that his experiments on the explosion of inflammable air with common and dephlogisticated air were made in the summer of 1781. The production of fixed air was at this time regarded as the invariable result of phlogistication, or, as we should call it, of the deoxidation of atmospheric air. Cavendish readily disproved the correctness of this view, and he began to inquire what was the product of the combustion of hydrogen in air and in oxygen. Dr. Priestley and Warltire, a lecturer on natural philosophy in Birmingham, were experimenting on the same subject with a detonating tube, and they observed a deposition of moisture to follow each explosion. Priestley does not appear to have paid any attention to this phenomenon, and Warltire referred it to the condensation of water which had existed in a state of vapour in the gases. The hypothesis that phlogiston was present in all combustibles led Priestley and La Place astray, and the appearance of nitric acid—the composition of which was quite unknown in 1784—in the condensed water tended to involve the problem. Cavendish, by most ingenious experiments, proved that the nitric acid was formed from the atmospheric nitrogen present in the detonating globe, and demonstrated that the only product of the combustion of pure hydrogen and oxygen was pure water. In his own words he came to the conclusion that water consists of dephlogisticated air (oxygen) united with phlogiston (hydrogen). He was thus the first who, by purely inductive experiments, converted oxygen and hydrogen into water, and who taught that water consisted of these gases. He must also be regarded as the discoverer of nitric acid. In the history of chemistry we do not find any discovery which has led to the same amount of angry discussion as that which followed the important announcement by Cavendish in his Experiments on Air, which were begun in 1777 or 1778, but which were not published until 1783.
     On 15 Jan. 1784 the Experiments on Air, by Henry Cavendish, Esq., was read before the Royal Society. An interpolation by Dr. Blagden (who for some time acted as secretary to Cavendish), after the paper was read, states that all the experiments on the explosion of inflammable air with common and dephlogisticated airs were made in the summer of 1781. Cavendish himself commences his paper Experiments on Air by stating that his experiments were made with a view to find out the cause of the diminution which common air is well known to suffer, by all the various ways in which it is phlogisticated, and to discover what becomes of the air thus lost or consumed. To this he adds subsequently that his experimental results, beyond determining this fact, also throw light on the constitution and means of production of dephlogisticated air. This question excited much attention among the chemists of Europe in 1777. Priestley and Scheele about the same time discovered oxygen, and this gas was regarded by them as air perfectly respirable, and exhibiting its great power of supporting combustion, because it was deprived of phlogiston. It was, in accordance with this hypothesis, named by chemists dephlogisticated air. For some time the atmosphere was believed to consist of two parts of dephlogisticated air (our oxygen) and one part of phlogisticated air (our nitrogen). Cavendish resolved on ascertaining with precision the true constitution of the aerial fluid. With this object in view he burnt various bodies in measured quantities of air, confined over water at first, and then over mercury. As early as 1766 Cavendish had satisfied himself of the constant composition of the atmosphere. With his usual care he prosecuted this inquiry. Dr. Priestley and his friend Warltire repeated and modified Cavendish's experiments, and in 1781 Priestley refers to Warltire's observations on the moisture left by burning inflammable air. Warltire is said to have burned the gases in a close vessel by means of electricity, weighing the vessel before and after the explosion, observing the dewy deposit and finding only a very trifling loss of weight. Mr. James Patrick Muirhead, in his Correspondence of the late James Watt, volunteers the information that there appears no conclusion as to the real origin of water published (in 1781) by Mr. Cavendish, nor communicated to any individual, nor contained in the journal and notes of his experiments; nor alleged by himself, nor by any one else, to have been then drawn by him. In 1766 Cavendish employed hydrogen and air, and he then noticed a certain amount of liquid being found in the flask in which the gases were exploded, and he unhesitatingly concludes that almost all the inflammable air, and about one-fifth of the common air, lose their elasticity and are condensed into the dew which lines the glass. His full conclusion was that this dew is plain water, and consequently that almost all the inflammable air, and about one-fifth of the common air, are turned into pure water. Watt, Dr. Priestley, Dr. Black, Mr. de Luc, M. la Place, M. Lavoisier, and others were deeply interested in the phlogistic hypothesis, and all of them were in constant communication, meeting in scientific societies or corresponding with each other. Cavendish, it must be regretted, did not pursue his brilliant career with any activity. He led a strangely retired life, and consequently he frequently was left in ignorance of the progress of discovery. Cuvier, in his éloge on Cavendish, said of him, his demeanour and the modest tone of his writings procured him the uncommon distinction of never having his repose disturbed either by jealousy or by criticism.
     Arago, on the contrary, brought before the French Academy of Sciences a direct charge of deceit and plagiarism, affirming that Cavendish learned the composition of water by obtaining a sight of a letter from Watt to Priestley.
     The researches of Cavendish were communicated to Dr. Priestley before 24 June 1781; even Watt's son does not doubt this. On 26 March 1783 Watt mentions as new to him Priestley's experiment on exploding the gases by electricity. On 21 April in the same year Watt writes to Dr. Black, and on 26 April to Dr. Priestley, his conclusion that water is composed of dephlogisticated and inflammable air. Dr. Priestley received this letter in London, submitted it to Sir Joseph Banks, president of the Royal Society, and to Dr. Blagden, the intimate friend of Cavendish, and his secretary. This letter was to have been read before the Royal Society, but Watt requested that the public reading of it might be delayed until he should examine some new experiments, said by Dr. Priestley to contradict his theory.
     Cavendish's memoir having been read 15 Jan. 1784, Watt's first letter was, according to his own request, read at the Royal Society on 22 April, his second letter being read on 29 April. In these communications Watt writes, referring to Dr. Priestley: If my deductions have any merit, it is to be attributed principally to the perspicuity, attention, and industry with which you have pursued the experiments which gave birth to them, and to the candour with which you receive the communications of your friends. From this it is evident that Watt himself admits his obligations to Dr. Priestley, and we have seen that Cavendish and Priestley were friendly correspondents; consequently it may safely be concluded that the speculations on the composition of water were the common subjects of talk in the scientific societies of London and Birmingham.
     J. A. De Luc [q.v.], the Genevese philosopher, was a fellow of the Royal Society at this time, and it was from him that Watt first heard of Cavendish's paper. Weld, the assistant secretary, in his ‘History of the Royal Society,’ says that ‘in July of the same year his paper was printed in the “Transactions,” bearing the erroneous date of 1784 instead of 1783, which stands upon the manuscript.’ Many were deceived, and among them Cuvier, by this error. As soon as it was discovered, Cavendish wrote to the editor of one of the principal foreign journals to correct it. The discussion which prevailed for some time in France and England as to the priority of Cavendish or Watt as discoverers was unpleasantly aggravated by the errors of the dates printed, and yet more so by two interpolations, made after the reading of Cavendish's paper, by Dr. Blagden, who was appointed secretary to the Royal Society on 5 May 1784, and to whom was entrusted the superintendence of the printing of both Watt's letters, and who made the interpolations in Cavendish's contribution.
     The only conclusion to which we can arrive is, that both Cavendish and Watt made about the same time experiments on air and water; that they framed hypotheses which were of an analogous character, differing mainly in respect to elementary heat, which Watt regarded as a material entity, but which Cavendish rejected as insufficient to account for the observed phenomena. They both worked honestly, in ignorance of each other's studies, and they both arrived at similar conclusions.
     If Cavendish had been more communicative, there is no doubt he would have avoided the annoyance of the claims made by Watt and other investigators to a discovery the merit of which was justly his own. It is satisfactory to record that in 1785 Watt became a fellow of the Royal Society; he then formed the acquaintance of Cavendish, and they terminated their scientific rivalries in the most amicable manner.
     It is necessary to mention a ‘Mémoire où l'on prouve par la décomposition de l'eau, que ce fluide n'est point une substance simple,’ &c., by MM. Meusnier et Lavoisier, printed in 1784; a second paper on the same subject by Lavoisier alone; and a ‘Mémoire sur le résultat de l'inflammation du gaz inflammable et de l'air déphlogistiqué dans des vaisseaux clos,’ par M. Monge, printed in 1786. There is, however, satisfactory evidence to prove that the French chemists had been previously informed of the discoveries of Cavendish and Watt.
     The use of light in promoting the growth of plants was most carefully investigated by Cavendish, but the conclusions which he drew from his experiments were vitiated by the theory of phlogiston, which had not yet been entirely abandoned.
     The views entertained by Cavendish on specific and latent heat greatly advanced our views, and, associated with the fine investigations made by Dr. Black, paved the way to the more philosophical deductions of the present day.
     After 1785, Cavendish made no new discoveries. His papers on heat, the original records of which prove that this investigation was commenced in 1764, were written out for the use of a friend, but he published no part of them until nineteen years after most of the experiments had been completed, and then a trifling portion only appears incidentally in a paper on the ‘Freezing of Mercury,’ read at the Royal Society in 1783.
     It has been suggested that the reason why those researches on heat were never published was that Cavendish had considerable reluctance to enter into even the appearance of rivalry with Dr. Black.
     In 1772 and in 1776 Cavendish was engaged in investigating the principal phenomena of electricity, and two papers on the subject appear in the ‘Philosophical Transactions.’ These papers contain the first distinct statement of the difference between animal and common electricity, and twenty-seven propositions upon the action of the electric fluid, treated mathematically. Besides those two papers Cavendish left behind him some twenty packets of manuscript essays on mathematical and experimental electricity. Of these Sir William Snow Harris states that ‘Cavendish had really anticipated all those great facts in common electricity which were subsequently made known to the scientific world through the investigations of Coulomb and other philosophers, and had also obtained the more immediate results of experiments of a more refined kind instituted in our own day.’
     On 21 June 1798 a paper by Cavendish was read before the Royal Society entitled ‘Experiments to determine the Density of the Earth.’ The Rev. John Michell had suggested a method for doing this, and had constructed the apparatus which was in the main adopted by Cavendish, with several improvements. It occurred to him that this force could be measured by accurately observing the action of bodies suddenly presented in the neighbourhood of a horizontal lever, 40 inches long, nicely balanced, and loaded with leaden balls of equal size, about 2 inches diameter, at its two ends, and protected from any current of air. Two heavy spherical masses of metal were then brought near to the balls, so that their attractions conspired in drawing the lever aside. From the known weight of the mass of metal, the distance of the centres of the mass and of the ball, and the ascertained attraction, it was not difficult to determine the attraction of an equal spherical mass of water upon a particle as heavy as the ball placed on its surface, and from this can be found the attraction of a sphere of water of the same diameter as the earth, upon the ball placed on its surface. The experiments made were few; seventeen only are recorded. From these Cavendish deduced twenty-three results, from the mean of which he computed the density of the earth to be equal to 5×45.
     The accuracy of Cavendish's observations is shown by the fact that Reich, professor of natural philosophy at Freiberg in Saxony, after fifty-seven experiments came to the conclusion that the density of the earth was 5×44. Francis Baily [q.v.] repeated Cavendish's experiments with similar apparatus, somewhat modified. The final result obtained by Baily was 5×660. Sir George Airy in May 1826 carried out a series of pendulum experiments in Harton Colliery, and determined the mean density of the earth as 6×566.
     A paper on the civil year of the Hindus should be mentioned in order to show the varied character of Cavendish's investigations. The mass of manuscripts which he left behind him proves that nearly every subject which in his time engaged the attention of the chemist or of the natural philosopher had been closely studied by him. The ‘Catalogue of Scientific Papers of the Royal Society’ credits Cavendish with sixteen memoirs. Watt assigns him eighteen. The personal history of this great philosopher is told in his works. He was a man of reserved disposition, a shy habit, and many singularities of manner. Added to these a difficulty of speech, and a thin, shrill voice, increased his dislike of society, and his avoidance of conversation.
     Cavendish lived on Clapham Common, his large library being some distance from his house. He allowed friends the free use of his books, but he himself never took a book from it without leaving a receipt behind. His large income was allowed to accumulate, and his habits were of the most inexpensive kind. He received no stranger at his residence, he ordered his dinner daily by a note left on the hall table, and from his morbid shyness he objected to any communication with his female domestics. He scarcely ever went into society. Lord Brougham says he had met him at the meetings of the Royal Society and at Sir Joseph Banks's weekly conversations, ‘and recollects the shrill cry he uttered as he shuffled quickly from room to room, seeming to be annoyed if looked at, but sometimes approaching to hear what was passing among others. His walk was quick and uneasy. He probably uttered fewer words in the course of his life than any man who ever lived to fourscore years, not at all excepting the monks of La Trappe.’      On all points which had not some scientific bearing Cavendish was coldly indifferent. When the discovery of a new truth was told to him, a glow of interest came over him. He was never known to express himself warmly on any question of religion or politics; indeed he appeared to reject all human sympathy.
     He died on 10 March 1810, after probably the only illness from which he ever suffered. Having ordered his servant not to come near him till night, he was all day alone. His servant found him apparently in a dying state, and immediately sent for Sir Everard Home. Cavendish told Sir Everard ‘that any prolongation of life would only prolong its miseries.’ He was buried in All Saints' Church, Derby. He left a fortune of 1,175,000l. His residuary legatee was his cousin, Lord George Cavendish, whose grandson was seventh Duke of Devonshire [see Supplement].

Sources:
     Philosophical Transactions, lxxiv. 119, 329, 354;
     Royal Soc. Cat. of Scientific Papers, and Supplement;
     Watt's Bibl. Brit.;
     Wilson's Life of Cavendish (Cavendish Society's Works), vol. i. 1846;
     Muirhead's Correspondence of Watt; Brougham's Lives of Philosophers of the time of George III, 1846; Weld's History of the Royal Society, vol. ii. 1848; Mémoires de l'Académie des Sciences, 1781, pp. 151, 171, 269; Arago's Éloge Historique de James Watt, 1839; British Association Reports, 1839, President's address.
Contributor: R. H-t. [Robert Hunt]

Published:     1886