18 HISTORY OF MECHANICS. 



properties of the wedge and the screw. And shortly 

 after this time, Galileo also established the same 

 results on different principles. In his Treatise Delle 

 Scienze Mecaniche (1592), he refers the inclined 

 plane to the lever, in a sound and nearly satisfac- 

 tory manner ; imagining a lever so placed, that the 

 motion of a body at the extremity of one of its 

 arms should be in the same direction as it is upon 

 the plane. A slight modification makes this an 

 unexceptionable proof. 



Sect. 3. Prelude to the Science of Dynamics. 

 Attempts at the First Law of Motion. 



WE have already seen, that Aristotle divided Mo- 

 tions into Natural and Violent. Cardan endea- 

 voured to improve this division by making three 

 classes; Voluntary Motion, which is circular and 

 uniform, and which is intended to include the celes- 

 tial motions: Natural Motion, which is stronger 

 towards the end, as the motion of a falling body ; 

 this is in a straight line, because it is motion to an 

 end, and nature seeks her ends by the shortest 

 road : and thirdly, Violent Motion, including in this 

 term all kinds different from the former two. Car- 

 dan was aware that such Violent Motion might be 

 produced by a very small force; thus he asserts, 

 that a spherical body resting on a horizontal plane 

 may be put in motion by any force which is suffi- 

 cient to cleave the air; for which, however, he 



