522 INDUCTION. 



the force, with a velocity proportioned to the force 

 directly, and to its own mass inversely ; when in point 

 of fact some bodies to which a force is applied do not 

 move at all, and those which do move are, from the 

 very first, retarded by the action of gravity and other 

 resisting forces, and at last stopped altogether ; it is 

 clear that the general proposition, although it would 

 be true under a certain hypothesis, would not express 

 the facts as they actually occur. To accommodate 

 the expression of the law to the real phenomena, we 

 must say, not that the object moves, but that it tends 

 to move in the direction and with the velocity speci- 

 fied. We might, indeed, guard our expression in a 

 different mode, by saying that the body moves in that 

 manner unless prevented, or except in so far as pre- 

 vented by some counteracting cause. But the body 

 does not only move in that manner unless counter- 

 acted ; it tends to move in that manner even when 

 counteracted ; it still exerts, in the original direction, 

 the same energy of movement as if its first impulse 

 had been undisturbed, and produces, by that energy, 

 an exactly equivalent quantity of effect. This is true 

 even when the force leaves the body as it found it, in 

 a state of absolute rest ; as when we attempt to raise 

 a body of three tons weight with a force equal to one 

 ton. For if, while we are applying this force, the wind 

 or water or any other agent supplies an additional 

 force just exceeding two tons, the body will be raised ; 

 thus proving that the force we applied exerted its full 

 effect, by neutralizing an equivalent portion of the 

 weight which it was insufficient altogether to over- 

 come. And if, while we are exerting this force of one 

 ton upon the object in a direction contrary to that of 

 gravity, it be put into a scale and weighed, it will be 

 found to have lost a ton of its weight, or, in other 



