36 l'KKSIl)E\TIAI> ADDRESS SECTIOX A 



Before going further, let me open a parenthesis : 

 Is that attraction, that gravitation, that action at a distance 

 stated by Newton's law, i-eal? This question does not interest 

 the physicist if there is no fact that may contradict the existence 

 of such an action. For the metaphysicist, the question is a 

 fundamental one. The aim of Science is to know the Truth. 

 For knowing it, man has at his disposal experience, observation 

 and ratiocination. 



The physicist, confronted by phenomena, tries to explain them 

 by the hypothesis that will bind the greatest number of them. 

 The metaphysicist searches for something more : he searches for 

 the nomena, i.e., the transcendental cause of pheiinuicna. 



Let me give you an example showing the difference between 

 the aims of the physicist and the metaphysicist : 



I let a stone fall; this may be explained in two ways, 

 namely : 



(a) The stone has a tendency to approach the soil; 



(b) The soil attracts the stone. 



To the physicist the two ways are equivalent, so long as he 

 knows no other phenomena ; to the metaphysicist they are not 

 only different, but contradictory, because the former ascribes the 

 cause of the fall to the stone, while the second one ascribes it 

 to the soil. 



When choosing between the two ways, the physicist investi- 

 gates which of them may include more phenomena, i.e., which 

 is more general. What interests him is the generality, not the 

 reality. 



But what is reality? Our knowledge of facts is given us by 

 our senses. Each of us sees the world in a manner in which it is 

 not possible to know if it is the same manner in which it is seen 

 by another. The world may have for each of us an aspect 

 thoroughly different from that which it has for another. Which 

 of these aspects is the true one? 



There are only three possible answers to this question: all, 

 none, only one. To each of them corresponds a meaning of the 

 word true. 



The first is the answer given by the physicist. He is not 

 interested in metaphysical speculations over the reality of the 

 world. He knows it only by the impressions which the objects 

 cause upon his mind ; for him, the external world exists only 

 within his conscience. 



Tln' law of gravitation is only an liypothesis giving an 

 explanation of a certain class of movements. So long as one of 

 these movements- does not contradict it, the physicist does not 

 doubt it. As you know, the ever-growing perfection of apparatus 

 caused some doubts to arise, but let me put this matter aside for 

 the moment. As to the reality of gravitation, we can only state 

 that the movement of a body is influenced by the vicinity of 

 otbev.-^. This influence may be explained both by a direct action 



