OF THE SPECIFIC GRAVITIES OF BODIES. 181 



be hung by horse-hairs, or by silk threads. So that a LECT 

 body, suspended by the hair or thread, may be im- v,^v^/ 

 mersed in water without wetting the scale from which 

 it hangs. 



If the body thus suspended under the scale, at one HOW to 

 end of the balance, be first counterpoised in air by j^^ 

 weights in the opposite scale, and then immersed in gravity of 

 water, the equilibrium will be immediately destroyed. aE 

 Then, if as much weight be put into the scale from 

 which the body hangs, as will restore the equilibrium, 

 (without altering the weights in the opposite scale) that 

 weight, which restores the equilibrium, will be equal to 

 the weight of a quantity of water as big as the im- 

 mersed body. And if the weight of the body in air be 

 divided by what it loses in water, the quotient will shew 

 how much that body is heavier than its bulk of water. 

 Thus, if a guinea, suspended in air, be counterbalanced 

 by 129 grains in the opposite scale of the balance ; and 

 then, upon its being immersed in water, it becomes so 

 much lighter, as to require 7j grains put into the scale 

 over it, to restore the equilibrium, it shews that a quan- 

 tity of water, of equal bulk with the guinea, weighs 

 7 g rains, or 7.25 ; by which divide 129 (the weight of 

 the guinea in air), and the quotient will be 17.793 ; 

 which shews that the guinea is 17.793 times as heavy 

 as its bulk of water. And thus any piece of gold may 

 be tried, by weighing it first in air, and then in water ; 

 and if, upon dividing the weight in air by the loss in 

 water, the quotient comes out to be 17.793, the gold is 

 good ; if the quotient be 18, or between 18 and 19, the 

 gold is very fine ; but if it be less than 17, the gold is 

 too much alloyed, by being mixed with some other 

 metal. 



If silver be tried in this manner, and found to be 11 

 times as heavy as water, it is very fine ; if it be 10$ times 

 as heavy, it is standard ; but if it be of any less weight 



