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.
