738 SCIENCE AND HYPOTHESIS 



them to the metaphysicians. That day has not yet come; man does 

 not so easily resign himself to remaining for ever ignorant of the 

 causes of things. Our choice cannot be therefore any longer guided 

 by considerations in which personal appreciation plays too large a 

 part. There are, however, solutions which all will reject because of 

 their fantastic nature, and others which all will prefer because of their 

 simplicity. As far as magnetism and electricity are concerned, Max- 

 well abstained from making any choice. It is not that he has a 

 systematic contempt for all that positive methods cannot reach, as 

 may be seen from the time he has devoted to the kinetic theory of 

 gases. I may add that if in his magnum opu& he develops no complete 

 explanation, he has attempted one in an article in the Philosophical 

 Magazine. The strangeness and the complexity of the hypotheses he 

 found himself compelled to make, led him afterwards to withdraw it. 

 The same spirit is found throughout his whole work. He throws 

 into relief the essential i.e., what is common to all theories ; every- 

 thing that suits only a particular theory is passed over almost in 

 silence. The reader therefore finds himself in the presence of form 

 nearly devoid of matter, which at first he is tempted to take as a 

 fugitive and unassailable phantom. But the efforts he is thus com- 

 pelled to make force him to think, and eventually he sees that there 

 is often something rather artificial in the theoretical " aggregates " 

 which he once admired. 



Electro-Dynamics 



The history of electro-dynamics is very instructive from our point 

 of view. The title of Ampere's immortal work is, Theorie des phe- 

 nomenes electro-dynamiques, uniquement fondee sur experience. He 

 therefore imagined that he had made no hypotheses; but as we shall 

 not be long in recognizing, he was mistaken; only, of these hypothe- 

 ses he was quite unaware. On the other hand, his successors see 

 them clearly enough, because their attention is attracted by the weak 

 points in Ampere's solution. They made fresh hypotheses, but this 

 time deliberately. How many times they had to change them before 

 they reached the classic system, which is perhaps even now not quite 

 definitive, we shall see. 



I. Ampere's Theory. In Ampere's experimental study of the 

 mutual action of currents, he has operated, and he could operate only, 

 with closed currents. This was not because he denied the existence 

 or possibility of open currents. If two conductors are positively and 

 negatively charged and brought into communication by a wire, a cur- 

 rent is set up which passes from one to the other until the two po- 

 tentials are equal. According to the ideas of Ampere's time, this was 

 considered to be an open current; the current was known to pass 



