C 469 3 
XXI. Experiments to determine the Density of the Earth. By 
Henry Cavendish, Esq. F.R.S. and A.S. 
Read June 21, 1798. 
IVIany years ago, the late Rev. John Michell, of this Society, 
contrived a method of determining the density of the earth, by 
rendering sensible the attraction of small quantities of matter ; 
but, as he was engaged in other pursuits, he did not complete 
the apparatus till a short time before his death, and did not 
live to make any experiments with it. After his death, the 
apparatus came to the Rev. Francis John Hyde Wollaston, 
Jacksonian Professor at Cambridge, who, not having conveni- 
ences for making experiments with it, in the manner he could 
wish, was so good as to give it to me. 
The apparatus is very simple ; it consists of a wooden arm, 
6 feet long, made so as to unite great strength with little 
weight. This arm is suspended in an horizontal position, by 
a slender wire 40 inches long, and to each extremity is hung a 
leaden ball, about 2 inches in diameter ; and the whole is in- 
closed in a narrow wooden case, to defend it from the wind. 
As no more force is required to make this arm turn round 
on its centre, than what is necessary to twist the suspending 
wire, it is plain, that if the wire is sufficiently slender, the most 
minute force, such as the attraction of a leaden weight a few 
inches in diameter, will be sufficient to draw the arm sensibly 
aside. The weights which Mr. Michell intended to use were 
