18. Experiments to deterniine the Density of the Earth. Phil. Trans.1798. P. 469. • The apparatus, with which this highly important investigation was conducted, had been invented and constructed many years before by the Reverend John Michell, who did not live to perform the experiments for which he intended it. Mr Cavendish, however, by the accu racy and perseverance with which he carried on a course of observations of so delicate a nature, as well as by the skill and judgment with which he obviated the many unforeseen difficulties that occur• red in its progress, and determined the corrections of various kinds which it was necessary to apply to the has deserved• no less gratitude from the cul tivators of astronomy and geography, than if the idea had originally been his own. The method em ployed was to suspend, by a vertical wire, a horizon• tal bar, having a leaden ballUt each end% to deter mine the magnitude of the force of torsion by the time occupied in the lateral vibrations of the bar; and to measure the extent of the change produced in its situation by the attraction of two large masses of lead, placed on opposite sides of the case contain ing the apparatus, so that this attraction might be compared with the weight of the balls, or, in other *ords, with the attraction of the earth. In this manner the mean density of the earth was found to be 51, times as great as that of water ; and although this is :considerably more than had been inferred from Dr Maskelyne's observations on the aurae' tion of ShebaIlion, yet the experiments agree so well with each other, that we can scarcely suppose any material error to have affected them. Mr Michell's apparatus resembled that which M. Coulomb had employed iu his experiments on magnetism, but he appears to have invented it before the publication of M. Coulomb's Memoirs. a . 19. On an Improved Method of Dividing Astrono mical Instruments. Phil. Trans. 1809. P. 221. The merits of this improvement have not been very highly appreciated by those who are in the habit of execu ting the divisions of circular arcs. It consists in a mode of employing a microscope, with its cross wires, as a substitute for one of the points of a beam corn pus, while another point draws a faint line on the face a the instrument in the usual manner. The Duke de Chaulnes had before used microscopical eights for dividing circles; but his method more nearly resembled that which has been brought for wards in an improved form by Captain Hater; and Mr Cavendish, by using a single microscope only, seems to have sacrificed some advantages which the other methods appear to possess : but none of them has been very fairly tried ; and our artists have hitherto continued to adhere to the modes which they had previously adopted, and which it would perhaps have been difficult for them to abandon, even ;f they had been convinced of the advantages to be gained by some partial improvements.
Such were the diversified labours of a philosopher, who possessed a clearness of comprehension, and an acuteness of reasoning, which had been the lot of very few of his predecessors, since the days of Newton. Maclaurin and Waring, perhaps also Stirling and Len. den were incomparably greater mathematicians ; but 'none of them attempted to employ their powers of in• vestigation in the pursuit of physical discovery : Euler and Lagrange, on the Continent, had carried the ho. provements of analytical reasoning to an unparalleled extent, and they both, as well as Daniel Bernoulli and D'Alembert, applied these powers with marked success to the solution of a great variety of problems in me.. cbanics and in astronomy : but they made no experi mental discoveries of importance : and the splendid career of chemical investigation, which has since been pursued with a degree of success so unprecedented in history, may be said to have been first laid open to mankind by the labours of Mr Cavendish : although the further discoveries of Priestley, Scheele, and La, voisier, soon furnished, in rapid succession, a super structure commensurate to the extent,of the founda tions so happily laid. " Whatever the sciences reveal ed to Mr Cavendish," says•Cuvier, " appeared always to exhibit something of the sublime and the marvel. lous : he weighed the earth : he rendered the air na vigable: he deprived water of the quality of finale ment :" and he denied to fire the character of a sub. " The clearness of the evidence on which he established his discoveries, so new and so unexpected as they were, is still more astonishing than the facts themselves which be detected.: and the works, in which he has made them public, are so many master pieces of sagacity and of methodical reasoning: each perfect as a whole and in its parts ; and leaving nos thing for any hand to correct; but rising in splen •dour with each successive year that passes over them; and promising to carry down his name to a posterity far more remote than his rank and connections could ever have enabled him to attain without them."
In his manners Mr Cavendish had the appearance of a quickness and sensibility almost morbid, united to a slight hesitation in his speech, which seems to have depended more on the constitution of his mind, than on any deficiency of his organic powers, and to an air of timidity and reserve, which sometimes af forded a contrast, almost ludicrous, to the sentiments of profound respect which were professed by those with whom he conversed. It is not impossible that he may have been indebted to his love of severe study, not only for the decided superiority of his faculties to those of the generality of mankind, but even for his exemption from absolute eccentricity of character. His person was tall, and rather thin : his dress was singularly uniform, although sometimes a little glected. His pursuits were seldom interrupted by in disposition ; but he suffered occasionally from cal culous complaints. His retired habits of life, and his disregard of popular opinion, appear to have lessened the notoriety which might otherwise have attached to his multiplied successes in science ; but his merits were more generally understood on the Continent than in this country ; although it was not till he bad pas sed the age of seventy, that he was made one of the eight Foreign Associates of the Institute of France.
Mr Cavendish was no less remarkable in the latter part of his life, for the immense accumulation of his pecuniary property, than for his intellectual and scien tific treasures. His father died in 1788 ; being at that time eighty years old, and the senior member of the Royal Society : but he is said to have succeeded at an earlier period to a considerable inheritance left him by one of his uncles. He principally resided at Clapham Common ; but his library was latterly at his house in Bedford Square; and his books were at the command of all men of letters, either personally known to him, or recommended by his friends: indeed the whole ar. rangement was so impartially methodical, that be ne ver took down a book for his own use, without enter. ing it in the loan book ; and after the death, of a German gentleman, who had been his librarian, he appointed a day on which be attended in person every week for the accommodation of the few, who thought themselves justified in applying to him for such books as they wished to consult. lie was constantly pre sent at the meetings of the Royal Society, as well as at the conversations held at the house of the President ; and he dined every Thursday with the club composed of its members. He had little intercourse with gene ral society, or even with his own family, and saw only once a year the person whom he had made his princi pal heir. He is said to have assisted several young men, whose talents recommended them to his notice, in obtaining establishments in life ; but in his Intel years, such instances were certainly very rare. His tastes and his pleasures do not seem to have been ip unison with those, which are best adapted to the ge nerality of mankind ; and amidst the abundance of all the means of acquiring every earthly enjoyment, he must have wanted that sympathy, which alone is ca. pible of redoubling our delights, by the consciousness that we share them in common with a multitude of our friends,.and of enhancing the beauties of all the bright prospects that surround us, when they arc still more highly embellished by reflection " from looks that we love." He could have had no limitation ei ther of comfort or of luxury. to stimulate him to ex ertion; even his riches must have deprived him of the gratification of believing, that each new triumph in science might promote the attainment of some great 'object in life that he earnestly desired ; a gratification generally indeed illusory, but which does not cease to be guile us till we become callous as well to the pleasures as to the sorrows of existence. But in the midst of this " painful preeminence," he must still have been ca pable of extending his sensibility over a still wider field of time and space, anti of looking forwards to the approbation of the wise and the good of all countries and of all ages: and he roast have enjoyed the high est and purest of all intellectual pleasures, arising from the consciousness of his own excellence, and from the certainty that, sooner or later, all mankind must ac knowledge his claim to their profoundest respect and highest veneration.