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On The Heavens   

when nothing hinders, and in the case of the thing healed, when

nothing stays the healing. But the movement is also due to the

original creative force and to that which removes the hindrance or off

which the moving thing rebounded, as was explained in our opening

discussions, where we tried to show how none of these things moves

itself. The reason of the various motions of the various bodies, and

the meaning of the motion of a body to its own place, have now been



We have now to speak of the distinctive properties of these bodies

and of the various phenomena connected with them. In accordance with

general conviction we may distinguish the absolutely heavy, as that

which sinks to the bottom of all things, from the absolutely light,

which is that which rises to the surface of all things. I use the term

'absolutely', in view of the generic character of 'light' and 'heavy',

in order to confine the application to bodies which do not combine

lightness and heaviness. It is apparent, I mean, that fire, in

whatever quantity, so long as there is no external obstacle moves

upward, and earth downward; and, if the quantity is increased, the

movement is the same, though swifter. But the heaviness and

lightness of bodies which combine these qualities is different from

this, since while they rise to the surface of some bodies they sink to

the bottom of others. Such are air and water. Neither of them is

absolutely either light or heavy. Both are lighter than earth-for

any portion of either rises to the surface of it-but heavier than

fire, since a portion of either, whatever its quantity, sinks to the

bottom of fire; compared together, however, the one has absolute

weight, the other absolute lightness, since air in any quantity

rises to the surface of water, while water in any quantity sinks to

the bottom of air. Now other bodies are severally light and heavy, and

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