12 Britain's Heritage of Science 



phenomenon from which everything else should be derived. 

 In France, at any rate, the influence of Descartes' philosophy 

 was paramount, and Descartes had truly started from the 

 beginning : " I think, therefore I exist," was to him the 

 only justifiable & priori assertion to make ; everything else 

 was to be deduced from that proposition. With a most 

 powerful and original intellect, he had developed an ingenious 

 and in many ways logical and consistent system, in which 

 there was no room for the motion of any body except that 

 which was brought about by the impulse of another body 

 which itself was in motion. If the planets revolve round 

 the sun, it was to him, therefore, clear that they must be 

 carried along by an invisible medium whirling round the 

 sun. Hence his hypothesis of gigantic vortices filling all 

 space. This is not the place to explain how all phenomena 

 in Nature were supposed to be accounted for by such means, 

 but it is clear that the hypothesis was elastic, and could be 

 varied, added to, and infinitely extended, whenever some 

 difficulty arose. What concerns us here is that it seemed 

 to go to the foundation of things the origin of motion 

 and to those trained up in the doctrine of vortices, the mere 

 postulate of a universal attraction to account for one set 

 of natural phenomena, disregarding all the rest, seemed to 

 be a retrograde step. Hence very naturally arose consider- 

 able opposition, and it was mainly those who disagreed with 

 Descartes and believed in the possibility of action at a- 

 distance, who inclined towards Newton. But this was 

 really beside the point, because Newton expressly guards 

 himself against the implication that his theory necessarily 

 involved action at a distance, the origin of gravitational 

 force being in no way prejudged by the afiirmation of its 

 existence. We have here an example of the often re- 

 curring struggle between a general but indefinite hypothesis 

 which suggests many things, but cannot be submitted to a 

 numerical test, and what is characteristic of the Cambridge 

 school of investigation. This school, which had its period 

 of triumph in the nineteenth century, clearly defines a 

 problem, confining it to such limits, wide or narrow, as will 

 convert it into a precise problem which can be formulated 

 and submitted to mathematical analysis. There must 



