102 PHYSICAL SCIENCES IN ANCIENT GREECE. 



of a Fluid, as a body of which the parts are per- 

 fectly moveable among each other by the slightest 

 partial pressure, and in which all pressure exerted 

 on one part is transferred to all other parts. From 

 this idea of Fluidity, necessarily follows that mul- 

 tiplication of pressure which constitutes the hydro- 

 static paradox; and the notion being seen to be 

 verified in nature, the consequences were also rea- 

 lized as facts. This notion of Fluidity is expressed 

 in the postulate which stands at the head of Archi- 

 medes's " Treatise on Floating Bodies." And from 

 this principle are deduced the solutions, not only 

 of the simple problems of the science, but of some 

 problems of considerable complexity. 



The difficulty of holding fast this Idea of Flu- 

 idity so as to trace its consequences with infallible 

 strictness of demonstration, may be judged of from 

 the circumstance that, even at the present day, 

 men of great talents, not unfamiliar with the sub- 

 ject, sometimes admit into their reasonings an over- 

 sight or fallacy with regard to this very point. 

 The importance of the Idea when clearly appre- 

 hended and securely held, may be judged of from 

 this, that the whole science of Hydrostatics in its 

 most modern form is only the developement of the 

 Idea. And what kind of attempts at science would 

 be made by persons destitute of this Idea, we may 

 see in the speculations of Aristotle concerning light 

 and heavy bodies, which we have already quoted ; 



