NATURE AND LAW. 371 



attracted by it, dotvnwards^ so it is a "property" of smoke to 

 mount upwards. But this is nothing more than another form of 

 stating the facts famihar to everybody. Such philosophers as talk 

 of laws " explaining " phenomena, or of the " potencies " of matter 

 as giving a sufficient account of its activities, seem to me not to 

 have got beyond that " wisdom of the Ancients," which, in such 

 a case as that just cited, they would themselves repudiate as mere 

 " folly." 



The notion of the attractive force of the earth, unchecked by 

 any right conception of the action of force in producing motion, 

 led the Ancients into a very strange error. As the " weight " of a 

 body is the expression of the downward " pull " which the earth 

 exerts upon it, it seemed natural to suppose that the rate of the 

 fall of any heavy body to the ground would increase in proportion to 

 that weight, so that a body weighing ten pounds would fall ten times 

 as fast as a body weighing one pound. And this was formulated 

 as a "law" by Aristotle, and accepted by "educated" mankind 

 as such for nearly two thousand years : for although it might 

 have been at once disproved by the very simple experiment of 

 letting fall the two weights at the same moment from the top of a 

 high tower, and observing when they respectively struck the ground 

 at the bottom, the authority of Aristotle on the one hand (to doubt 

 which was rank heresy),^ and what seemed the " common sense 

 of the matter " on the other, prevented it from being called in 

 question. 



Here again (as it seems to me) we may find a lesson of great 

 value. Aristotle was undoubtedly — as regards science — the 

 " master mind " of the ancient philosophy ; but in this matter 

 he proceeded upon his own conceptions, instead of upon ascer- 

 tained facts ; and he consequently presumed to make laws for 

 Nature, instead of setting himself to determine what are the laws 

 of Nature — framing general expressions of what he thought must 

 be her orderly uniformities, instead of inquiring what these 

 uniformities really are, and basing his generalizations upon them. 



It was by Galileo that this matter was first experimentally 

 investigated. While yet a student in medicine at the University 

 of Pisa (his native town), his attention was attracted by the swing- 

 Lag of one of the chandeliers from the lofty roof of the Cathedral, 



