EQUILIBRIUM OF FLUIDS. 153 



6. If two fluids (not capable of mixing) are contained in a bent tube, and 

 balance each other, their perpendicular altitudes, measured from the same 

 horizontal plane, will be reciprocally as their specific gravities. 



7. (1.) The specific gravities of bodies are in the same proportion as their 

 weights, when their sizes are equal. 



(2.) When the weights are equal, the specific gravities are inversely 

 as their sizes. 



(3.) When the specific gravities are equal, their weights are directly 

 as their sizes. 



(4.) When neither the sizes nor the specific gravities are equal, the 

 weights of bodies are as their sizes and specific gravities together. 



8. A solid immersed in a fluid, will sink if its specific gravity be greater than 

 that of the fluid ; if less, it will float on the surface. 



9. The entire weight of a body which will float in a fluid, is equal to the 

 weight of as much of the fluid as the immersed part of the body displaces. 



Therefore, as the size of the whole body, is to the size of the part immersed, 

 so is the specific gravity of the fluid, to the specific gravity of the body. 



I have previously described the operation of computing the specific gravity 

 of a gas ; I shall now point out the methods to be pursued in finding the spe- 

 cific gravities of liquid and solid bodies, which it may frequently be useful 

 to know. 



When the body is heavier than water (which is taken here as the standard 

 of comparison, as air in the case of a gaseous fluid), weigh it both in water, and 

 out of water, and the difference of these weights will express the weight lost 

 in water. Then, if its weight is five out of the water, and when immersed 

 three, the weight lost will be two. The rule will be, 



As 2, the weight lost in water, is to 5, the absolute weight, so is I'O, the 

 specific gravity of water, to 2'5, the specific gravity of the body. 



When the body is lighter than water, attach to it a piece of another body 

 heavier than water, so that they may sink together. Weigh the heavier 

 body and the compound body separately, both out of the water and in it, and 

 find how much each loses in water, but subtracting its weight in water from 

 its weight in air, and subtract the less of these remainders from the greater. 

 Then use this proportion : 



As the last remainder, is to the weight of the light body in air, so is the 

 specific gravity of water, to the specific gravity of the body. 



