CHAPTER X. 



OF THE SPECIFIC GRAVITIES OF FLUIDS, AND THE METHOD OF 

 WEIGHING SOLID BODIES BY MEANS OF NON-ELASTIC FLUIDS. 



THE specific gravity of a body is its weight compared with that of another body 

 of the same magnitude. The magnitude may be expressed by a number denoting its 

 relation to some standard generally used, and as a criterion of comparison, similar 

 to itself, as a cubical inch, a foot, &c. ; and if the criteria be different, as in solids 

 and fluids, the magnitudes of bodies are to each other as the criteria multiplied 

 into the numbers expressing these magnitudes. The clear and scientific expositions 

 which in the last chapter were given of absolute and relative weight, must have 

 well prepared the reader for entering upon the doctrine of specific gravities, which 

 distinguishes different species of matter from each other, in one of their most 

 obvious properties, namely, the weight of matter contained in a given space. The 

 weight of any portion of matter is easily ascertained ; but it is not always easy to 

 measure the space occupied by a body, or its magnitude; and in some instances 

 this cannot well be effected without artificial means. We employ for this purpose 

 distilled water, the specific gravity of which, or weight of a given bulk, is nearly 

 at all times the same. Adopting, therefore, this pure homogeneous substance as 

 our criterion or unit of measure, by comparing it with other substances the ratio of 

 their specific gravities may be easily discovered ; and denoting the specific gravity 

 of water by any number taken at pleasure, the numbers expressing the specific 

 gravities of other bodies are hence given, or, at least, assignable. 



PROPOSITION V. 



264. When a solid body is immersed in a fluid of different 

 specific gravity from itself: 



The weight which the body loses, will be to its whole 

 weight, as the specific gravity of the fluid is to the specific 

 gravity of the solid. 



This is a very important proposition in hydrostatics, but its demon- 

 stration does not require the assistance of a diagram ; we must there- 

 fore endeavour to establish its validity by the application of symbolical 

 arithmetic ; for which purpose 



