iv.j MODERN SCIENCE 331 



quintessence, all the rest of this period being filled by the 

 passage, of no interest in itself, from one form to another 

 form. Take, for instance, a falling body. It was thought 

 that we got near enough to the fact when we characterized 

 it as a whole: it was a movement downward; it was the 

 tendency toward a centre; it was the natural movement 

 of a body which, separated from the earth to which it be- 

 longed, was now going to find its place again. They noted, 

 then, the final term or culminating point (riXos, dK/jtrj) and 

 set it up as the essential moment: this moment, that 

 language has retained in order to express the whole of 

 the fact, sufficed also for science to characterize it. In the 

 physics of Aristotle, it is by the concepts " high" and " low," 

 spontaneous displacement and forced displacement, own 

 place and strange place, that the movement of a body shot 

 into space or falling freely is defined. But Galileo thought 

 there was no essential moment, no privileged instant. To 

 study the falling body is to consider it at it matters not 

 what moment in its course. The true science of gravity 

 is that which will determine, for any moment of time what- 

 ever, the position of the body in space. For this, indeed, 

 signs far more precise than those of language are required. 

 We may say, then, that our physics differs from that of 

 the ancients chiefly in the indefinite breaking up of time. 

 For the ancients, time comprises as many undivided periods 

 as our natural perception and our language cut out in it 

 successive facts, each presenting a kind of individuality. 

 For that reason, each of these facts admits, in their view, 

 of only a total definition or description. If, in describing 

 it, we are led to distinguish phases in it, we have several 

 facts instead of a single one, several undivided periods in- 

 stead of a single period ; but time is always supposed to be 

 divided into determinate periods, and the mode of division 

 to be forced on the mind by apparent crises of the real, 



