ARISTOTELIAN PHYSICS. 51 



imagined that, in this way, they defined what was 

 absolutely (airXa>9) heavy and light." We now know 

 that things which rise by their lightness do so only 

 because they are pressed upwards by heavier sur- 

 rounding bodies ; and this assumption of absolute 

 levity, which is evidently gratuitous, or rather 

 merely nominal, entirely vitiated the whole of the 

 succeeding reasoning. The inference was, that fire 

 must be absolutely light, since it tends to take its 

 place above the other three elements ; earth abso- 

 lutely heavy, since it tends to take its place below 

 fire, air, and water. The philosopher argued also, 

 with great acuteness, that air, which tends to take 

 its place below fire and above water, must do so by 

 its nature, and not in virtue of any combination of 

 heavy and light elements. " For if air were com- 

 posed of the parts which give fire its levity, joined 

 with other parts which produce gravity, we might 

 assume a quantity of air so large, that it should be 

 lighter than a small quantity of fire, having more 

 of the light parts." It thus follows that each of the 

 four elements tends to its own place, fire being the 

 highest, air the next, water the next, and earth the 

 lowest. 



The whole of this train of errors arises from 

 fallacies which have a verbal origin; from consi- 

 dering light as opposite to heavy; and from con- 

 sidering levity as a quality of a body, instead of 

 regarding it as the effect of surrounding bodies. 



It is worth while to notice that a difficulty which 



E2 



