334 CREATIVE EVOLUTION iohap. 



magnitudes : the volume of a body, the density of the liquid 

 in which the body is immersed, the vertical pressure that 

 is being exerted. And it states indeed that one of these 

 three terms is a function of the other two. 



The essential, original difference must therefore be sought 

 elsewhere. It is the same that we noticed first. The 

 science of the ancients is static. Either it considers in 

 block the change that it studies, or, if it divides the change 

 into periods, it makes of each of these periods a block in its 

 turn: which amounts to saying that it takes no account 

 of time. But modern science has been built up around 

 the discoveries of Galileo and of Kepler, which immediately 

 furnished it with a model. Now, what do the laws of 

 Kepler say? They lay down a relation between the areas 

 described by the heliocentric radius-vector of a planet and 

 the time employed in describing them, a relation between 

 the longer axis of the orbit and the time taken up by the 

 course. And what was the principle discovered by Galileo? 

 A law which connected the space traversed by a falling 

 body with the time occupied by the fall. Furthermore, 

 in what did the first of the great transformations of geometry 

 in modern times consist, if not in introducing — in a veiled 

 form, it is true — time and movement even in the considera- 

 tion of figures? For the ancients, geometry was a purely 

 static science. Figures were given to it at once, completely 

 finished, like the Platonic Ideas. But the essence of the 

 Cartesian geometry (although Descartes did not give it 

 this form) was to regard every plane curve as described 

 by the movement of a point on a movable straight line 

 which is displaced, parallel to itself, along the axis of the 

 abscissae — the displacement of the movable straight line 

 being supposed to be uniform and the abscissa thus be- 

 coming representative of the time. The curve is then 

 defined if we can state the relation connecting the space 



