538 DISSERTATION ON 



movements it may make. And, in natural fabllances, the feed is the 

 firft caufe of the motions by which a' plant is produced ; but it is by 

 other principles of motion that the plant grows, is nourifhed, and fub- 

 fifts; And in animals, the parent is the efficient caufe of the offspring, 

 but only as the origin of the motion by which it is produced, not as 

 the caufe of the after motions of the animal, by which it continues to 

 exift. 



It is alfo commonly faid, that the motion is communicated by the 

 body that gives the impulfe to the other body ; and that it is by this 

 communicated motion that the other body is moved: But this, when 

 attentively confidered, is faying no more than that the body impelled 

 is moved by the other body, and with a velocity in proportion to the 

 impelling force, which therefore is faid to be communicated to it in a 

 certain decree. 



It remains, therefore, only to confider the hypothefis, that the body, 

 after the impulfe has ceafed, continues to be moved by a certain 

 power, which is of the nature and eflence of matter, and is therefore 

 called by Sir Ifaac a vis in/it a, or inherent force. This, as I have ob- 

 ferved, is a notion very dangerous to the dodrine of Theifm, and 

 therefore ought to be very carefully examined. 



And, in xhtfrji place, I afk, If there be a principle of motion eflen- 

 tial to matter, why does not that principle move the body, while it is 

 at reft, as well as continue its motion after it is once moved I 



Secnndo, I afk, Why do not the Newtonians account alfo for 

 gravitation by this principle of felf-motion ? Why fliould it be 

 confined only to projedion ? And, indeed, it appears to me, that 

 no other reafon needs be given for all the motions of the univcrfe. 

 Although thcfe motions be different, in difFeren< bodies, and different 



in 



