| that all Matter is Heavy, e71 
Nabe has . 
fallacy in this reasoning, for it proves a state of things to be necessary 
when we can so easily conceive a contrary state of things. Is it denied, 
the opponent may ask, that we can readily imagine a state of things in 
which bodies have no weight? Is not the uniform tendency of all bodies 
in the same direction not only not necessary, but not even true? For 
they do in reality tend, not with equal forces in parallel lines; but to 
a centre with unequal forces, according to their position: and we can 
conceive these differences of intensity and direction:in the force to be 
greater than they really are ; and can with equal ease suppose the force 
to disappear altogether. POM 
“To this I reply, that certainly we may conceive the weight of bodies 
to-vary in intensity and direction, and by an additional effort of imagi- 
nation may conceive the weight to vanish: but that in all these suppo- 
sitions, even in the extreme one, we must suppose the rule to be uni- 
versal. If any bodies have weight, all bodies must have weight. If 
the direction of weight be different in different points, this direction 
must still vary according to the law of continuity ; and the same is true 
of the intensity of the weight. For if this were not so, the rest and 
motion, the velocity and direction, the permanence and change of bod- 
ies, as to their mechanical condition, would be arbitrary and incohe- 
rent: they would not be subject to mechanical ideas ; that is, not to 
ideas at all; and hence these conditions of objects would in fact be 
inconceivable. In order that the universe may be possible, that is, may 
fall under the conditions of intelligible conceptions, we must be able to 
conceive a body at rest. But the rest of bodies (except in the absolute 
negation of all force) implies the equilibrium of opposite forces. And 
one of these opposite forces must be a general force, as weight, in order 
that the universe may be governed by general conditions. And this 
general force, by the conception of force, may produce motion, as well 
as equilibrium ; and this motion again must be determined, and deter- 
mined by general conditions ; which cannot be, except the communi- 
cation of motion be regulated by an inertia proportional to the weight. 
“¢ But it will be asked, Is it then pretended that Newton’s experiment, 
by which it was intended to prove inertia proportional to weight, does 
really prove nothing but what may be demonstrated @ priori? Could 
we know, without experiment, that all bodies,—gold, iron, wood, cork,— 
have inertia proportional to their weight ¢ And to this we reply, that 
xperiment holds the same place in the establishment of this, as of the 
other fundamental doctrines of mechanics. Intercourse with the external 
World is requisite for developing our ideas ; measurement of phenomena 
is needed to fix our conceptions and to render them precise; but the 
‘Tesult of our experimental studies is, that we reach a position in which 
