118 HYDROSTATICS. 



Since gold is the heaviest of all known metals, it 

 must be of less bulk, according to its weight, than 

 any other metal. And therefore he desired that a 

 mass of pure gold, equally heavy with the crown 

 when weighed in air, should be weighed against 

 it in water, and if the crown was not alloyed, he 

 conceived it would counterpoise the mass of gold 

 when they were both immersed in water, as well 

 as it did when they were weighed in air. But 

 upon making the trial, he found that the mass of 

 gold weighed much heavier in water than the crown 

 did; and not only so, but that, when the mass and 

 crown were immersed separately in one vessel of 

 water, the crown raised the water much higher 

 than the mass did; which showed it to be alloyed 

 with some lighter metal that increased its bulk. 



A body immersed in a fluid will sink to the 

 bottom, if it be heavier than its bulk of the fluid. 

 If it be suspended therein, it will lose as much of 

 what it weighed in air, as its bulk of the fluid 

 weighs. Hence, all bodies of equal bulks, which 

 would sink in fluids, lose equal weights when sus- 

 pended therein ; and unequal bodies lose in pro- 

 portion to their bulks. 



The instrument used for finding the specific gra 

 vities of bodies, is called the hydrostatic balance. 

 (Plate 8. fig. 8.) 



It differs very little from a common balance that 

 is nicely made; only it has a hook at the bottom of 

 one of the scales, on which different substances 

 that are to be examined may be hung by horse- 

 hairs, or silk threads, so as to be immersed in a 

 vessel of water, without wetting the scale. 



If a body thus suspended under the scale at one 

 end of the balance, be first counterpoised in air by 

 weights in the opposite scale, and then immersed in. 



