U^ I^HE PHiLOSOPfit 



CHAPTER IV. 



^,, Of Motion, 



JViOTION, in the opinion of Ariftotle, and tli6 

 admirers of ancient philofophy, can only be produced by 

 mind ; and hence they define 7nind to be X\\q power of mov^ 

 ing. By the fame mode of reafoning, it may be faid that ref^ 

 or inaBivity^ is the power of being moved. But fuch fpeculations 

 are foreign to the nature of this work, and perhaps fruitlefs 

 in themfelves. Though it is impoffible to give an unexcep- 

 -^ionable definition of motion, the phaenomenon itfelf is ob- 

 vious to every man's fenfes. 



All the terreftrial objects which prefent themfelves to our 

 obfervation are, with regard to motion, diflinguifhable into 

 two general clafles. The firfi: confifts of thofe which are 

 endowed with a fpontaneous or felf-moving power, and with 

 fome qualities and affedtions fimilar to thofe of our minds. 

 The fecond confifts of all thofe obje£ls in which no fuch 

 qualities and afFe£lions appear, and are of a nature fo paffive, 

 that they never move of themfelves, nor, when put in mo- 

 tion, do they ever ftop without fome external influence or 

 refiftance. The firfl: clafs of obje6ts, from their pofTeffing 

 the pov/er of fpontaneous motion, and other qualities pecu- 

 liar to animated beings, are eafily diftinguiflied from body, 

 or matter, which is totally deprived of all thefe qualities. 

 In confequence of its paffive nature, matter not only never 

 changes its ftate without external force, but refifls when any 

 fuch change is attempted to be made. When at refl, it can- 

 not be put in motion without dfficulty ; and, when in mo- 

 tion, a certain force is required to ftop its courfe. The 

 force with which matter perfeveres in its ftate, and refifls 



