~PHYSICAL ann LITERARY. 73 
Place any mafs of fuch a fubftance at reft. It 
cannot begin motion of itfelf by the fuppofiti- 
on. Butan adtive animated being, as for exam- 
ple, a man, can move it. Some effort mutt 
certainly be made, fome power exerted, to 
produce this effect. It will never be pretend- 
ed, that tht fame effort can move the mafs ei- ° 
_ ther with a great velocity or a {mall velocity ; 
that being as abfurd, as to fay that a great ve- 
thing. In like manner, it muft require one 
effort to move a {mall quantity of this fub- 
{tance with a certain velocity, and a differ- 
ent effort to move agreat quantity with the 
fame velocity. The fame energy of the a 
gent; will never ferve to move a given nett 
4 tity of this fubftance, or double the quanti- 
ty of this fubftance, with the fame velocity ; 
: locity anda {mall velocity are one and the fame 
no more than it will move the fame fub- 
ftance with different velocities. By this ex- 
- ertion of our own. activity, we acquire the 
ideas of forces. The animated being (or 
the mind) is differently affected by different 
ob whether of the fenfes or under- 
pare: And why fhould it be affeéted 
_ the fame way, when a great fub- 
Kai ftance 
