MECHANICS AND HYDROSTATICS. 103 



where, by considering light and heavy as opposite 

 qualities, residing in things themselves, and by an 

 inability to apprehend the effect of surrounding 

 fluids in supporting bodies, the subject was made 

 a -mass of false or frivolous assertions, which the 

 utmost ingenuity could not reconcile with facts, and 

 could still less deduce from the asserted doctrines 

 any new practical truths. 



In the case of Statics and Hydrostatics, the 

 most important condition of their advance was un- 

 doubtedly the distinct apprehension of these two 

 appropriate Ideas, Statical Pressure, and Hydrosta- 

 tical Pressure as included in the idea of Fluidity. 

 For the Ideas being once clearly possessed, the 

 experimental laws which they served to express 

 (that the whole pressure of a body downwards was 

 always the same ; and that water, and the like, 

 were fluids according to the above idea of fluidity) 

 were so obvious, that there was no doubt nor dif- 

 ficulty about them, These two ideas lie at the 

 root of all mechanical science; and the firm pos- 

 session of them is, to this day, the first requisite 

 for a student of the subject. After being clearly 

 awakened in the mind of Archimedes, these ideas 

 slept for many centuries, till they were again called 

 up in Galileo, and more remarkably in Stevinus. 

 This time, they were not destined again to slum- 

 ber; and the results of their activity have been 

 the formation of two Sciences, which are as certain 



