For some considerable time after this, Cavendish appears to have laid aside Chemistry for other departments of physics. In 1771 he published an elaborate paper on the theory of the principal phenomena of electricity; and in 1776 appeared the curious and interesting account of his attempts to imitate the effects of the torpedo, by an apparatus constructed in imitation of the living fish, and placed in connection with a frictional electrical machine and a Leyden battery. In this imitation he succeeded so well, that all doubts were removed as to the identity of the torpedinal benumbing power with common electricity. In 1776 Cavendish was selected by the Royal Society, in whose 'Transactions' all his previous papers had been published, to describe the various meteorological instruments which were made use of in their apartments; and the succeeding year to this marks the period when he commenced his most important chemical researches, entitled 'Experiments on Air,' which were carried on with frequent and sometimes long interruptions until 1788, no part of them, however, having been published before the year 1783. They led to the discovery of the constant quantitative composition of the atmosphere, the compound nature of water, and the composition of nitric acid. To solve the important problems, whether the atmosphere is constant in its composition, and if so, what is its composition? Cavendish experimented in 1781 for some sixty successive days, making many hundred analyses of air. The honour of the discovery of the compound nature of water, by which perhaps his name has become most famous, is also claimed by James Watt. Cavendish, however, seems at all events entitled to the honour of having first supplied the data on which that discovery was founded, whilst Watt appears to have supplied the conclusion.
Between the years 1783 and 1788, Cavendish published his papers on 'Heat,' and his 'Experiments on Air;' the former are three in number, and relate chiefly to the phenomena of congelation, and embody some of the results of experiments made as early as the year 1764. The first of these papers refer to quicksilver, demonstrating the true freezing-point of this metal to be 39° or 40° below zero, while the second and third refer to the freezing of the mineral acids and of alcohol.
His experiments on air, which led to the important results already referred to, supplied materials for four papers, besides leading to the observation of many phenomena which were never made public. With the last of these papers published in 1788, Cavendish closed his chemical researches, his remaining publications referring to meteorology and astronomy.
In 1798 appeared the celebrated enquiry into the density of the earth, communicated by Cavendish, in a paper to the Royal Society, in which he determined, by means of an apparatus contrived by the Rev. John Mitchell, the density of our globe to be 5·4,—or, in other words, nearly five-and-a half times heavier than the same bulk of water would be. The experiments made with this apparatus consisted in observing, with many precautions, the movements of a long lever delicately suspended by the centre, so as to hang horizontally, and furnished at either extremity with small leaden balls. When two much larger and heavier balls of the same metal were brought near the smaller ones, the latter were attracted towards them with a certain force, the measurement of which supplied one essential datum for the determination of the mean density of the earth. No greater compliment to the accuracy of the 'Cavendish Experiment' (as the researches taken as a whole are generally called) can be afforded, than the slight difference which appeared when the experiment was repeated at a later period by Francis Baily, who, with extraordinary precautions to ensure a correct result, and with all the improvements which forty fertile years had added to mechanical contrivances, determined the density to be 5·6, or a little more than five-and-a-half times that of water.
The last paper which Cavendish published, on an improvement in the manner of dividing astronomical instruments, appeared in 1809,—a year before his death. His published papers give, however, but an imperfect notion of the great extent of ground over which he travelled in the course of his investigations, and of the success with which he explored it. He was an excellent mathematician, electrician, astronomer, meteorologist, and geologist, and a chemist equally learned and original. He lived retired from the world among his books and instruments; he never meddled with the affairs of active life, but passed his whole time in storing his mind with the knowledge imparted by former inquirers, and in extending its bounds. His dress was of the oldest fashion; his walk was quick and uneasy; he never appeared in London unless lying back in the corner of his carriage; and he probably uttered fewer words in the course of his life than any man who ever lived to fourscore years. His private character has been thus described by Dr. George Wilson, from whose comprehensive life of Cavendish the present memoir has been chiefly taken:—
"Morally it was a blank, and can only be described by a series of negations. He did not love, he did not hate, he did not hope, he did not fear, he did not worship as others do. He separated himself from his fellow men, and apparently from God. There was nothing earnest, enthusiastic, heroic or chivalrous in his nature; and as little was there anything mean, grovelling or ignoble. He was almost passionless. An intellectual head thinking, a pair of wonderfully acute eyes observing, and a pair of very skilful hands experimenting or recording, are all that I recognize in his memorials. His brain seems to have been but a calculating engine; his eyes inlets of vision, not fountains of tears; his hands instruments of manipulation, which never trembled with emotion, or were clasped together in adoration, thanksgiving or despair; his heart only an anatomical organ necessary for the circulation of the blood. A sense of isolation from his brethren made him shrink from their society and avoid their presence; but he did so as one conscious of an infirmity, not boasting of an excellence. He was like a deaf mute, sitting apart from a circle whose looks and gestures show that they are uttering and listening to music and eloquence, in producing or welcoming which he can be no sharer. Wisely therefore he dwelt apart. He was one of the unthanked benefactors of his race, who was patiently teaching and serving mankind, whilst they were shrinking from his coldness or mocking his peculiarities. He could not sing for them a sweet song, or create a 'thing of beauty,' which would be 'a joy for ever,' or touch their hearts, or fire their spirits, or deepen their reverence or their fervour. He was not a poet, a priest, or a prophet, but only a cold clear intelligence, raying down pure white light, which brightened everything on which it fell, but warmed nothing—a star of at least the second, if not of the first magnitude in the intellectual firmament."
As Cavendish had lived, so he died—alone. He died after a short illness, probably the first as well as the last under which he ever suffered. His habit of curious observation continued to the end; he was desirous of marking the progress of disease and the gradual extinction of the vital powers. With this view, that he might not be disturbed, he desired to be left alone. His servant returning sooner than he had wished was ordered again to leave the chamber of death, and when he came back a second time he found his master had expired. Although in many respects of a highly liberal character, so great was the frugality of his ordinary mode of living in comparison to his income, that at his death Cavendish left the enormous sum of 1,200,000l. to be divided among his relations.—Life of the Hon. Henry Cavendish, by George Wilson, M.D., F.R.S.E. London, 1851.—Brougham's Lives of Philosophers. London and Glasgow, 1855.
WILLIAM CHAPMAN, M.R.I.A.
Born 1749. Died May 29, 1832.