712 SCIENCE AND HYPOTHESIS 



proved. The geometrical sum of all the forces applied to all the 

 molecules would no longer be zero. If we did not wish to change the 

 whole of the science of mechanics, we should have to introduce the 

 ether, in order that the action which matter apparently undergoes 

 should be counterbalanced by the re-action of matter on something. 



Or again, suppose we discover that optical and electrical phenomena 

 are influenced by the motion of the earth. It would follow that those 

 phenomena might reveal to us not only the relative motion of material 

 bodies, but also what would seem to be their absolute motion. Again, 

 it would be necessary to have an ether in order that these so-called 

 absolute movements should not be their displacements with respect 

 to empty space, but with respect to something concrete. 



Will this ever be accomplished? I do not think so, and I shall 

 explain why ; and yet, it is not absurd, for others have entertained this 

 view. For instance, if the theory of Lorentz, of which I shall speak 

 in more detail in Chapter XIII., were true, Newton's principle would 

 not apply to matter alone, and the difference would not be very far 

 from being within reach of experiment. On the other hand, many 

 experiments have been made on the influence of the motion of the 

 earth. The results have always been negative. But if these experi- 

 ments have been undertaken, it is because we have not been certain 

 beforehand; and indeed, according to current theories, the compensa- 

 tion would be only approximate, and we might expect to find accurate 

 methods giving positive results. I think that such a hope is illusory; 

 it was none the less interesting to show that a success of this kind 

 would, in a certain sense, open to us a new world. 



And now allow me to make a digression; I must explain why I 

 do not believe, in spite of Lorentz, that more exact observations will 

 ever make evident anything else but the relative displacements of ma- 

 terial bodies. Experiments have been made that should have dis- 

 closed the terms of the first order; the results were nugatory. 

 Could that have been by chance ? No one has admitted this ; a general 

 explanation was sought, and Lorentz found it. He showed that the 

 terms of the first order should cancel each other, but not the terms 

 of the second order. Then more exact experiments were made, which 

 were also negative; neither could this be the result of chance. An ex- 

 planation was necessary, and was forthcoming; they always are; hypo- 

 theses are what we lack the least. But this is not enough. Who is 

 there who does not think that this leaves to chance far too important a 

 role? Would it not also be a chance that this singular concurrence 

 should cause a certain circumstance to destroy the terms of the first 

 order, and that a totally different but very opportune circumstance 

 should cause those of the second order to vanish? No; the same 

 explanation must be found for the two cases, and everything tends to 

 show that this explanation would serve equally well for the terms of 



