NEWTON S PBIXCIFIA. 163 



remaining sections, treat of the pressure and motion of 

 fluids themselves and propagated in pulses, or otherwise, 

 through fluids. We shall arrange the subjects under these 

 Five heads, instead of following the precise order of the 

 work itself.* 



Two observations are applicable to this branch of the 

 subject, and to the treatment of it in the Principia ; and 

 these observations lead to our distinguishing this portion 

 of that great work from the rest. 



First. Much more had been accomplished of discovery 

 respecting the dynamics of fluids before the time of Sir 

 Isaac Newton, in proportion to the whole body of the 

 science, than in the other branches of Mechanics. The 

 Newtonian discoveries, therefore, effected a less consider 

 able change upon this department of Physics than upon 

 Physical Astronomy and the general laws of motion. As 

 early as the time of Archimedes the fundamental principle 

 of the general or undequaque pressure of fluids had been 

 ascertained ; many of the easier problems, and even some 

 of the more complicated, had been investigated bv its aid. 

 When dynamical science was newly constructed by the 

 illustrious Galileo, the progress which he made may almost 

 be said to have formed Hydrostatics and Hydraulics into a, 

 system ; and Pascal s original and inventive genius, soon 

 afterwards applied to it, enabled him clearly to perceive 

 the hydrostatic paradox, and even led him to a plain an 

 ticipation of the hydrostatic press. f Torricelli about the 

 same period reduced the atmosphere under the power of 

 weight and measure, making it the subject of calculation by 

 the beautiful experiment which first ascertained its gravity, 



* For the arrangement, see the Summary of Contents, 

 t He calls a box of water &quot;a new mechanical principle by which we may 

 multiply force ad libitum.&quot; (Eqoil. of Fluids, 1653.) 



M 2 



