the Density oj the Earth. 
The attraction of the weight on the furthest ball, in the di- 
rection bw, is to its attraction on the nearest ball : : wd % : zcD 3 
• : ,0017 : 1 ; and therefore the effect of the attraction of the 
weight on both balls, is to that of its attraction on the nearest 
ball : : ,9983 : 1. 
To find the attraction of the copper rod on the nearest ball, 
let b and w (fig. 6 . ) be the centres of the ball and weight, and 
ea the perpendicular part of the copper rod, which consists of 
two parts, ad and de . ad weighs 22000 grains, and is 1G 
inches long, and is nearly bisected by w. de weighs 4,1000, 
and is 4 6 inches long, wb is 8,85 inches, and is perpendicular 
to .ew. Now, the attraction of a line ew, of uniform thickness, 
on b, 111 the direction bw, is to that of the same quantity of 
matter placed at w : : bw : eb; and therefore the attraction of 
the part da equals that of or j^oo, pl ace d at w; 
and the attraction of de equals that of 41000 x - 41000 
dw b w 
x TiT x TT ’ or 2 5 °°. placed at the same point ; so that the at- 
traction of the perpendicular part of the copper rod on b, is to 
that of the weight thereon, as 18800 : 2439000, or as ,00771 
to 1. As for the attraction of the inclined part of the rod and 
wooden bar, marked P r and rr in fig. 1, it may safely be 
neglected, and so may the attraction of the whole rod on the 
arm and farthest ball; and therefore the attraction of the 
weight and copper rod, on the arm and both balls together, ex- 
ceeds the attraction of the weight on the nearest ball, in the 
proportion of ,3983 -f- ,0139 -f ,0077 to one, or of 1,0199 to 1. 
The next thing to be considered, is the attraction of the rna- 
hogany case. Now it is evident, that when the arm stands at 
3 U 2 
