iv.j MODERN SCIENCE 333 



forms replacing forms; it is content with a qualitative de- 

 scription of objects, which it likens to organized beings. 

 But when we seek to know what happens within one of 

 these periods, at any moment of time, we are aiming at 

 something entirely different. The changes which are pro- 

 duced from one moment to another are no longer, by the 

 hypothesis, changes of quality; they are quantitative vari- 

 ations, it may be of the phenomenon itself, it may be of its 

 elementary parts. We were right then to say that modern 

 science is distinguishable from the ancient in that it applies 

 to magnitudes and proposes first and foremost to measure 

 them. The ancients did indeed try experiments, and on 

 the other hand Kepler tried no experiment, in the proper 

 sense of the word, in order to discover a law which is the 

 very type of scientific knowledge as we understand it. 

 What distinguishes modern science is not that it is experi- 

 mental, but that it experiments and, more generally, works 

 only with a view to measure. 



For that reason it is right, again, to say that ancient 

 science applied to concepts, while modern science seeks 

 laws — constant relations between variable magnitudes. 

 The concept of circularity was sufficient to Aristotle to 

 define the movement of the heavenly bodies. But, even 

 with the more accurate concept of elliptical form, Kepler 

 did not think he had accounted for the movement of planets. 

 He had to get a law, that is to say, a constant relation be- 

 tween the quantitative variations of two or several elements 

 of the planetary movement. 



Yet these are only consequences — differences that follow 

 from the fundamental difference. It did happen to the 

 ancients accidentally to experiment with a view to measur- 

 ing, as also to discover a law expressing a constant relation 

 between magnitudes. The principle of Archimedes is a 

 true experimental law. It takes into account three variable 



