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On The Heavens   

fire to move upward. If it were, the greater the quantity of fire

the slower it would move, owing to the increase of weight due to the

increased number of triangles. But the palpable fact, on the contrary,

is that the greater the quantity, the lighter the mass is and the

quicker its upward movement: and, similarly, in the reverse movement

from above downward, the small mass will move quicker and the large

slower. Further, since to be lighter is to have fewer of these

homogeneous parts and to be heavier is to have more, and air, water,

and fire are composed of the same triangles, the only difference being

in the number of such parts, which must therefore explain any

distinction of relatively light and heavy between these bodies, it

follows that there must be a certain quantum of air which is heavier

than water. But the facts are directly opposed to this. The larger the

quantity of air the more readily it moves upward, and any portion of

air without exception will rise up out of the water.

So much for one view of the distinction between light and heavy.

To others the analysis seems insufficient; and their views on the

subject, though they belong to an older generation than ours, have

an air of novelty. It is apparent that there are bodies which, when

smaller in bulk than others, yet exceed them in weight. It is

therefore obviously insufficient to say that bodies of equal weight

are composed of an equal number of primary parts: for that would

give equality of bulk. Those who maintain that the primary or atomic

parts, of which bodies endowed with weight are composed, are planes,

cannot so speak without absurdity; but those who regard them as solids

are in a better position to assert that of such bodies the larger is

the heavier. But since in composite bodies the weight obviously does

not correspond in this way to the bulk, the lesser bulk being often

superior in weight (as, for instance, if one be wool and the other

bronze), there are some who think and say that the cause is to be

found elsewhere. The void, they say, which is imprisoned in bodies,

lightens them and sometimes makes the larger body the lighter. The

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