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:--