PRELUDE TO THE EPOCH OF GALILEO. 9 



We have already, in speaking of the Greek 

 School Philosophy, noticed the attempt to explain 

 some of the differences among Motions, by classify- 

 ing them into Natural Motions and Violent Mo- 

 tions; and we have spoken of the assertion that 

 heavy bodies fall quicker in proportion to their 

 greater weight. These doctrines were still retained: 

 yet the views which they implied were essentially 

 erroneous and unsound ; for they did not refer dis- 

 tinctly to a measurable Force as the cause of all 

 motion or change of motion ; and they confounded 

 the causes which produce, and those which pre- 

 serve, motion. Hence such principles did not lead 

 immediately to any advance of knowledge, though 

 efforts were made to apply them, in the cases both 

 of terrestrial Mechanics and of the motions of the 

 heavenly bodies. 



The effect of the Inclined Plane was one of the 

 first, as it was one of the most important, pro- 

 positions, on which modern writers employed them- 

 selves. It was found that a body, when supported 

 on a sloping surface, might be sustained or raised 

 by a force or exertion which would not have been 

 able to sustain or raise it without such support. 

 And hence, The Inclined Plane was placed in the 

 list of Mechanical Powers, or simple machines by 

 which the efficacy of forces is increased : the ques- 

 tion was, in what proportion this increase of effi- 

 ciency takes place. It is easily seen that the force 

 requisite to sustain a body is smaller, as the slope 



