PRELUDE TO THE EPOCH OF GALILEO. 17 



the equilibrium ; so that four balls on the longer 

 plane would balance two balls on the shorter plane, 

 or the weights would be as the lengths of the planes 

 intercepted by the horizontal line. 



Stevinus showed his firm possession of the truth 

 contained in this principle, by deducing from it the 

 properties of forces acting in oblique directions 

 under all kinds of conditions ; in short, he showed 

 his entire ability to found upon it a complete doc- 

 trine of equilibrium ; and upon his foundations, and 

 without any additional support, the mathematical 

 doctrines of Statics might have been carried to the 

 highest pitch of perfection they have yet reached. 

 The formation of the science was finished ; the ma- 

 thematical developement and exposition of it were 

 alone open to extension and change (A). 



The contemporaneous progress of the other 

 branch of mechanics, the Doctrine of Motion, inter- 

 fered with this independent advance of Statics ; and 

 to that we must now turn. We may observe, how- 

 ever, that true propositions respecting the composi- 

 tion of forces appear to have rapidly diffused them- 

 selves. The Tractatus de Motu of Michael Varro 

 of Geneva, already noticed, printed in 1584, had 

 asserted, that the forces which balance each other, 

 acting on the sides of a right-angled triangular 

 wedge, are in the proportion of the sides of the 

 triangle ; and although this assertion does not ap- 

 pear to have been derived from a distinct idea of 

 pressure, the author had hence rightly deduced the 

 VOL. ii. C 



