MECHANICAL PRINCIPLES OF FLUIDS. 345 



CHAPTER IV. 



DISCOVERY OF THE MECHANICAL PRINCIPLES OF FLUIDS. 



Sect. 1. Rediscovery of the Laius of Equilibrium of fluids. 



WE have already said, that the true laws of the equilibrium of fluids 

 were discovered by Archimedes, and rediscovered by Galileo and 

 Stevinus ; the intermediate time having been occupied by a vaguenes* 

 and confusion of thought on physical subjects, which made it impoo 

 sible for men to retain such clear views as Archimedes had disclosed. 

 Stevinus must be considered as the earliest of the authors of this re- 

 discovery ; for his work (Principles of Statik and Hydrostatik) was 

 published in Dutch about 1585 ; and in this, his views are perfectly 

 distinct and correct. He restates the doctrines of Archimedes, and 

 shows that, as a consequence of them, it follows that the pressure of 

 a fluid on the bottom of a vessel may be much greater than the 

 weight of the fluid itself : this he proves, by imagining some of the 

 upper portions of the vessel to be filled with fixed solid bodies, which 

 take the place of the fluid, and yet do not alter the pressure on the 

 base. He also shows what will be the pressure on any portion of a 

 base in an oblique position ; and hence, by certain mathematical arti- 

 fices which make an approach to the Infinitesimal Calculus, he finds 

 the whole pressure on the base in such cases. This mode of treating 

 the subject would take in a large portion of our elementary Hydro- 

 statics as the science now stands. Galileo saw the properties of fluids 

 no less clearly, and explained them very distinctly, in 1612, in his 

 Discourse on Floating Bodies. It had been maintained by the Aris- 

 totelians, that form was the cause of bodies floating ; and collaterally, 

 that ice was condensed water ; apparently from a confusion of thought 

 between rigidity and density. Galileo asserted, on the contrary, that 

 ice is rarefied water, as appears by its floating : and in support of this, 

 he proved, by various experiments, that the floating of bodies does 

 not depend on their form. The happy genius of Galileo is the more 

 remarkable in this case, as the controversy was a good deal perplexed 

 by the mixture of phenomena of another kind, due to what is usually 

 called capillary or molecular attraction. Thus it is a fact, that a ball 



