Cavendish,_Henry

Cavendish, Henry (1731-1810), English chemist and physicist, elder son of Lord Charles Cavendish, brother of the 3rd duke of Devonshire, and Lady Anne Grey, daughter of the duke of Kent, was born at Nice in October 1731. He was sent to school at Hackney in 1742, and in 1749 entered Peterhouse, Cambridge, which he left in 1753, without taking a degree. Until he was about forty he seems to have enjoyed a very moderate allowance from his father, but in the latter part of his life he was left a fortune which made him one of the richest men of his time. He lived principally at Clapham Common, but he had also a town-house in Bloomsbury, while his library was in a house in Dean Street, Soho; and there he used to attend on appointed days to lend the books to men who were properly vouched for. So methodical was he that he never took down a volume for his own use without entering it in the loan-book. He was a regular attendant at the meetings of the Royal Society, of which he became a fellow in 1760, and he dined every Thursday with the club composed of its members. Otherwise he had little intercourse with society; indeed, his chief object in life seems to have been to avoid the attention of his fellows. With his relatives he had little intercourse, and even Lord George Cavendish, whom he made his principal heir, he saw only for a few minutes once a year. His dinner was ordered daily by a note placed on the hall-table, and his women servants were instructed to keep out of his sight on pain of dismissal. In person he was tall and rather thin; his dress was old-fashioned and singularly uniform, and was inclined to be shabby about the times when the precisely arranged visits of his tailor were due. He had a slight hesitation in his speech, and his air of timidity and reserve was almost ludicrous. He was never married. He died at Clapham on the 24th of February 1810, leaving funded property worth £700,000, and a landed estate of £8000 a year, together with canal and other property, and £50,000 at his bankers.

Cavendish’s scientific work is distinguished for the wideness of its range and for its extraordinary exactness and accuracy. The papers he himself published form an incomplete record of his researches, for many of the results he obtained only became generally known years after his death; yet in spite of the absence of anything approaching self-advertisement he acquired a very high reputation within his own country and abroad, recognized by the Institute of France in 1803 when it chose him as one of its eight foreign associates. Arsenic formed the subject of his first recorded investigation, on which he was engaged at least as early as 1764, and in 1766 he began those communications to the Royal Society on the chemistry of gases, which are among his chief titles to fame. The first (Phil. Trans., 1766) consists of “Three papers containing experiments on Factitious Airs,” dealing mostly with “inflammable air” (hydrogen), which he was the first to recognize as a distinct substance, and “fixed air” (carbon dioxide). He determined the specific gravity of these gases with reference to common air, investigated the extent to which they are absorbed by various liquids, and noted that common air containing one part in nine by volume of fixed air is no longer able to support combustion, and that the air produced by fermentation and putrefaction has properties identical with those of fixed air obtained from marble. In the following year he published a paper on the analysis of one of the London pump-waters (from Rathbone Place, Oxford Street), which is closely connected with the memoirs just mentioned, since it shows that the calcareous matter in that water is held in solution by the “fixed air” present and can be precipitated by lime. Electrical studies seem next to have engaged his attention, and in 1771 and 1772 he read to the Royal Society his “Attempt to explain some of the principal phenomena of electricity by an elastic fluid,” which was followed in 1775 by an “Attempt to imitate the effects of the Torpedo (a fish allied to the ray)” (Phil. Trans., 1776). But these two memoirs contain only a part of the electrical researches he carried out between 1771 and 1781, and many more were found after his death in a number of sealed packets of papers. The contents of these for a long time remained unknown, but ultimately by permission of the duke of Devonshire, to whom they belonged, they were edited by James Clerk Maxwell and published in 1879 by the Cambridge University Press as the Electrical Researches of the Hon. Henry Cavendish. About 1777 or 1778 he resumed his pneumatic inquiries, though he published nothing on the subject till 1783. In that year he described a new eudiometer to the Royal Society and detailed observations he had made to determine whether or not the atmosphere is constant in composition; after testing the air on nearly 60 different days in 1781 he could find in the proportion of oxygen no difference of which he could be sure, nor could he detect any sensible variation at different places. Two papers on “Experiments with Airs,” printed in the Phil. Trans. for 1784 and 1785, contain his great discoveries of the compound nature of water and the composition of nitric acid. Starting from an experiment, narrated by Priestley, in which John Warltire fired a mixture of common air and hydrogen by electricity, with the result that there was a diminution of volume and a deposition of moisture, Cavendish burnt about two parts of hydrogen with five of common air, and noticed that almost all the hydrogen and about one-fifth of the common air lost their elasticity and were condensed into a dew which lined the inside of the vessel employed. This dew he judged to be pure water. In another experiment he fired, by the electric spark, a mixture of hydrogen and oxygen (dephlogisticated air), and found that the resulting water contained nitric acid, which he argued must be due to the nitrogen present as an impurity in the oxygen (“phlogisticated air with which it [the dephlogisticated air] is debased”). In the 1785 paper he proved the correctness of this supposition by showing that when electric sparks are passed through common air there is a shrinkage of volume owing to the nitrogen uniting with the oxygen to form nitric acid. Further, remarking that little was known of the phlogisticated part of our atmosphere, and thinking it might fairly be doubted “whether there are not in reality many different substances confounded together by us under the name of phlogisticated air,” he made an experiment to determine whether the whole of a given portion of nitrogen (phlogisticated air) of the atmosphere could be reduced to nitric acid. He found that a small fraction, not more than 1⁄120 th part, resisted the change, and in this residue he doubtless had a sample of the inert gas argon which was only recognized as a distinct entity more than a hundred years later. His last chemical paper, published in 1788, on the “Conversion of a mixture of dephlogisticated and phlogisticated air into nitrous acid by the electric spark,” describes measures he took to authenticate the truth of the experiment described in the 1785 paper, which had “since been tried by persons of distinguished ability in such pursuits without success.” It may be noted here that, while Cavendish adhered to the phlogistic doctrine, he did not hold it with anything like the tenacity that characterized Priestley; thus, in his 1784 paper on “Experiments on Air,” he remarks that not only the experiments he is describing, but also “most other phenomena of nature seem explicable as well, or nearly as well,” upon the Lavoisierian view as upon the commonly believed principle of phlogiston, and he goes on to give an explanation in terms of the antiphlogistic hypothesis.

Early in his career Cavendish took up the study of heat, and had he promptly published his results he might have anticipated Joseph Black as the discoverer of latent heat and of specific heat. But he made no reference to his work till 1783, when he presented to the Royal Society some “Observations on Mr Hutchins’s experiments for determining the degree of cold at which quicksilver freezes.” This paper, with others published in 1786 and 1788, is concerned with the phenomena attending the freezing of various substances, and is noteworthy because in it he expresses doubt of the supposition that “the heat of bodies is owing to their containing more or less of a substance called the matter of heat,” and inclines to Newton’s opinion that it “consists in the internal motion of the particles of bodies.” His “Account of the Meteorological Apparatus used at the Royal Society’s House” (Phil. Trans., 1776) contains remarks on the precautions necessary in making and using thermometers, a subject which is continued in the following year in a report signed by him and six others.

Cavendish’s last great achievement was his famous series of experiments to determine the density of the earth (Phil. Trans., 1798). The apparatus he employed was devised by the Rev. John Michell, though he had the most important parts reconstructed to his own designs; it depended on measuring the attraction exercised on a horizontal bar, suspended by a vertical wire and bearing a small lead ball at each end, by two large masses of lead. (See Gravitation.) The figure he gives for the specific gravity of the earth is 5.48, water being 1, but in fact the mean of the 29 results he records works out at 5.448. Other publications of his later years dealt with the height of an aurora seen in 1784 (Phil. Trans., 1790), the civil year of the Hindus (Id., 1792), and an improved method of graduating astronomical instruments (Id., 1809). Cavendish also had a taste for geology, and made several tours in England for the purpose of gratifying it.

A life by George Wilson (1818-1859), printed for the Cavendish Society in 1851, contains an account of his writings, both published and unpublished, together with a critical inquiry into the claims of all the alleged discoverers of the composition of water. Some of his instruments are preserved in the Royal Institution, London, and his name is commemorated in the Cavendish Physical Laboratory at Cambridge, which was built by his kinsman the 7th duke of Devonshire.

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