PHYSICAL AND LITERARY. 83 



given quantity of this fubftance, or 

 double the quantity of this fub fiance, with 

 the fame velocity ; no more than it w^ill 

 move the fame fubftance with different 

 velocities. By this exertion of our own 

 activity, we acquire the ideas of forces. 

 The animated being (or the mind) is 

 differently affecfled by different objedis, 

 whether of the lenfes or underftanding. 

 And why fhould it be affeded in the 

 fame way, when a great fubftance and a 

 little fubftance are moved by it, or 

 when a great velocity and a little velo- 

 city are imparted to the fame fubftance? 

 When we endeavour to communicate 

 motion to fuch a fubftance, we muft be 

 confcious of fome kind of feeling ; and 

 thefe feelings muft be different in different 

 Cafes. Thus the idea of refiftance, as it is 

 called, to motion, in the moft inadive 

 fubftance we can imagine, would be fug- 

 gefted to us from thefe perceptions, and 

 is precifely the fame with what we expe- 

 ^rience daily in handling of matter. Nor 

 loes it feem poflible to conceive an ex- 

 tended, impenetrable fubftance, divefted 

 this kind of refiftance from inertia. 



The 



