132 THE PHILOSOPHY 



ings, are eafily diflingulfhed from body, or matter, which is totally 

 deprived of all thefe qualities. In confequence of its paflive nature, 

 matter not only never changes its ftate without external force, but 

 refifts when any fuch change is attempted to be made. When at 

 reft, it cannot be put in motion without difficulty ; and, when in 

 motion, a certain force is required to flop its courfe. The force 

 with which matter perfeveres in its ftate, and refifts any change, is 

 called its vis inertiae, and is always proportional to the quantity of 

 matter in any particular body. When we double or triple a body, 

 we uniformly find, that the force requifite to move it with equal 

 celerity muft likewife be doubled or tripled. Thefe, and fimilar 

 fads, which are refults of perpetual experience, fhow that body is 

 equally indifferent to motion and reft ; that this indifference feems 

 to be the natural confequence of the moft abfolute inadivity ; arul 

 that the power of beginning motion is peculiar to adive and intel- 

 ligent beings. Leaving, therefore, all metaphyfical fpeculations oa 

 this fubjed, we ftiall. give fbme remarks upon the motions of ani- 

 mals. 



In general,, all the progreftive motions of animal's are performed 

 by the inftrumentality of mufcles, tendons, and articulations. The 

 operation of mufcles depends upon fome unknown influence derived 

 to them from the brain and nerves. Hence the brain and nerves 

 are the fources of every motion as well as of every fenfation. With 

 regard to the caufes which determine the adions of animals, thefe 

 muft be referred to fenfation, and the confequent exertions of intel- 

 led. The firft impreffion an objed makes upon our fenfations fti- 

 mulates us either to approach or retire from it, according as it ex- 

 cifes afFedion or averfion. Thefe motions neceffarily refult from 

 the firft impreffion made by the objed. But man, and many other 

 animals, have the power of refifting thefe original motives to adion, 

 and of remaining at reft, without either retiring or approaching. ' If 



