OF NATURAL HISTORY. 131 



CHAPTER IV. 



Of Motion. 



MOTION, in the opinion of Ariftotle, and the admirers of 

 ancient philofophy, can only be produced by mind ; and 

 hence they define mind to be the power of moving. By the fame 

 mode of reafoning, it may be faid that rejl, or inaciivity, is the poiver 

 of being moved. But fuch fpeculations are foreign to the nature of 

 this work, and perhaps fruitlefs in themfelves. Though it is impof- 

 fible to give an unexceptionable definition of motion, the phaeno- 

 menon ilfelf is obvious to every man's fenfes. 



All the terreftrial objedls which prefent themfelves to our obfer- 

 vation are, with regard to motion, diftinguifhable into two general 

 claffes. The firft confifts of thofe which are endowed with a fpon- 

 taneous or felf- moving power, and with fome qualities and affec- 

 tions fimilar to thofe of our minds. The fecond confifts of all thofe 

 objeGs in which no fuch qualities and affedions appear, and are of 

 a nature fo paffive, that they never move of themfelves, nor, when 

 put in motion, do they ever flop without fome external influence or 

 refiftance. The firft clafs of objedls, from their poffeifing the power 

 of fpontaneous motion, and other qualities peculiar to animated he- 

 I R 2 inG:s. 



