Page:Dictionary of National Biography volume 09.djvu/355

 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 Mathematics appear, from the numerous unpublished papers which are still in existence, to have been his favourite study.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’ (i.e. 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