m THE LAST HALF-CE^TUEY. 69 



that since equal amounts of motion have, 

 ex hypothesi, been produced, the amount 

 of motion in a body does not depend on 

 its speed alone, but on some property of 

 the body. To this the name of 'mass' 

 has been given. And since it seems rea- 

 sonable to suppose that a large quantity 

 of matter, moving slowly, possesses as 

 much motion as a small quantity moving 

 faster, < mass ' has been held to express 

 'quantity of matter.' It is further de- 

 monstrable that, at any given time and 

 place, the relative mass of any two bod- 

 ies is expressed by the ratio of their 

 weights. 



When all these great truths respecting 

 molar motion, or the movements of visible 

 and tangible masses, had been shown to 

 hold good not only of terrestrial bodies, 

 but of aU those which constitute the visi- 

 ble universe, and the movements of the 

 macrocosm had thus been expressed by a 

 general mechanical theory, there remained 



