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On The Heavens   



incidental. For the expulsion of the foreign body is an incident in

the compacting of the homogeneous. In choosing the shape, then, they

should have thought either of both functions or preferably of the

combining function. In addition, since hot and cold are contrary

powers, it is impossible to allot any shape to the cold. For the shape

given must be the contrary of that given to the hot, but there is no

contrariety between figures. That is why they have all left the cold

out, though properly either all or none should have their

distinguishing figures. Some of them, however, do attempt to explain

this power, and they contradict themselves. A body of large particles,

they say, is cold because instead of penetrating through the

passages it crushes. Clearly, then, that which is hot is that which

penetrates these passages, or in other words that which has fine

particles. It results that hot and cold are distinguished not by the

figure but by the size of the particles. Again, if the pyramids are

unequal in size, the large ones will not be fire, and that figure will

produce not combustion but its contrary.

From what has been said it is clear that the difference of the

elements does not depend upon their shape. Now their most important

differences are those of property, function, and power; for every

natural body has, we maintain, its own functions, properties, and

powers. Our first business, then, will be to speak of these, and

that inquiry will enable us to explain the differences of each from

each.



Book IV

1



WE have now to consider the terms 'heavy' and 'light'. We must ask

what the bodies so called are, how they are constituted, and what is

the reason of their possessing these powers. The consideration of

these questions is a proper part of the theory of movement, since we

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