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On The Heavens   

us. But if they went on to think of the world as formed on this

pattern all round, with a centre identically related to each point

on the extremity, they would have to admit that the extremity was

above and the centre below.) By absolutely light, then, we mean that

which moves upward or to the extremity, and by absolutely heavy that

which moves downward or to the centre. By lighter or relatively

light we mean that one, of two bodies endowed with weight and equal in

bulk, which is exceeded by the other in the speed of its natural

downward movement.


Those of our predecessors who have entered upon this inquiry have

for the most part spoken of light and heavy things only in the sense

in which one of two things both endowed with weight is said to be

the lighter. And this treatment they consider a sufficient analysis

also of the notions of absolute heaviness, to which their account does

not apply. This, however, will become clearer as we advance. One use

of the terms 'lighter' and 'heavier' is that which is set forth in

writing in the Timaeus, that the body which is composed of the greater

number of identical parts is relatively heavy, while that which is

composed of a smaller number is relatively light. As a larger quantity

of lead or of bronze is heavier than a smaller-and this holds good

of all homogeneous masses, the superior weight always depending upon a

numerical superiority of equal parts-in precisely the same way, they

assert, lead is heavier than wood. For all bodies, in spite of the

general opinion to the contrary, are composed of identical parts and

of a single material. But this analysis says nothing of the absolutely

heavy and light. The facts are that fire is always light and moves

upward, while earth and all earthy things move downwards or towards

the centre. It cannot then be the fewness of the triangles (of

which, in their view, all these bodies are composed) which disposes

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