402 Di/covery of Archimedes. [Book VII. 



art of determining the fpecific gravities of bodies is 

 ufually included, but this I have already been under 

 a necefiity of anticipating * in fome degree. Archi- 

 medes, among the ancients, accomplifhed the moft 

 remarkable difcoveries in this fcience. He is ho- 

 noured even at this day, as the inventor of the inge- 

 nious hydroftatic procefs, by which the purity or 

 bafenefs of a crown of gold was afcertained. Among 

 the moderns we are indebted to Gallileo, Torricelli, 

 Defcartes, Pafcal, Guglielmini, and Marietta, for the 

 beft information on this fubject j and by their expe- 

 riments (which arc as curious as they are decifive) we 

 are inftrufted in what we may expert or fear from the 

 power of fluids violently acted upon by the principle 

 of gravity, and in what manner and upon what prin- 

 ciples we may employ, for the ufe of man, the hy- 

 draulic machines. 



It has been obfervfd in another place, that the pro- 

 penfity which bodies have of approaching towards 

 the earth, or perhaps towards its center, is the only 

 caufe of what we term weight or gravity, and that it 

 is by the continual efforts which they make to obey 

 that law, that they prefs upon every obflacle which 

 impedes their progrefs. As fluids, like folid bodies, 

 are impelled by their gravity, fo in this cafe they prefs 

 upon every object which oppofes their fall j but from 

 their nature they prefs in a different manner from 

 folid bodies ; hence arife the peculiar phenomena into 

 which we are now to inquire. . 



Fluids are matters, the component parts of which 



* See Book I. Chap. III. It was neceflary to explain the na- 

 ture of fpecific gravity in that part of the work, both becaufe it 

 relates rather tc* bodies in general than to fluid fublhmces ; and 

 hcaufe the frequent allufions to it in the progress of the work 

 would not have been otherwife underilood. 



i are 



