70 THE GREEK SCHOOL PHILOSOPHY 



this way, tliey defined what was absolutely (owrXwj) heavy and light. 

 We now know that things which rise by their lightness do so only 

 because they are pressed upwards by heavier surrounding 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 

 absolutely 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 composed 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 considering light as opposite to heavy ; and from 

 considering 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 often embarrasses 

 persons on their entrance upon physical speculations, the difficulty 

 of conceiving that up and down are different directions in different 

 places, had been completely got over by Aristotle and the Greek 

 philosophers. They were steadily convinced of the roundness of the 

 earth, and saw that this truth led to the conclusion that all heavy 

 bodies tend in converging directions to the centre. And, they added, 

 as the heavy tends to the centre, the light tends to the exterior, " for 

 Exterior is opposite to Centre as heavy is to light." 13 



The tendencies of, bodies downwards and upwards, their weight, 

 their fall, their floating or sinking, were thus accounted for in a man- 

 ner which, however unsound, satisfied the greater part of the specula- 

 tive world till the time of Galileo and Stevinus, though Archimedes 

 in the mean time published the true theory of floating bodies, which 

 is very different from that above stated. Other parts of the doctrines 

 of motion were delivered by the Stagirite in the same spirit and with 

 the same success. The motion of a body which is thrown along the 



De Ccelo. iv. 4. 



