76 HISTORY OF MECHANICS. 



interest to these mechanical speculations, at the 

 period now under review. Indeed, it is not easy to 

 state separately, as our present object requires us 

 to do, the progress of Mechanics, and the progress 

 of Astronomy. Yet the distinction which we have 

 to make is, in its nature, sufficiently marked. It is, 

 in fact, no less marked than the distinction between 

 speaking logically and speaking truly. The framers 

 of the science of motion were employed in esta- 

 blishing those notions, names, and rules, in con- 

 formity to which all mechanical truth must be ex- 

 pressed ; but what was the truth with regard to the 

 mechanism of the universe remained to be deter- 

 mined by other means. Physical Astronomy, at 

 the period of which we speak, eclipsed and over- 

 laid theoretical Mechanics, as, a little previously, 

 Dynamics had eclipsed and superseded Statics. 



The laws of variable force and of curvilinear 

 motion were not much pursued, till the invention 

 of Fluxions and of the Differential Calculus again 

 turned men's minds to these subjects, as easy and 

 interesting exercises of the pow r ers of these new 

 methods. Newton's Principia, of which the first 

 two Books are purely dynamical, is the great ex- 

 ception to this assertion; inasmuch as it contains 

 correct solutions of a great variety of the most 

 general problems of the science; and, indeed, is, 

 even yet, one of the most complete treatises which 

 we possess upon the subject. 



We have seen that Kepler, in his attempts to 



