198 nutting: the ether 



The evidence against the existence of the ether falls into two 

 distinct classes; it is either evidence against the mechanical theory 

 or else evidence based on the negative results of attempts to detect 

 ether drift. In the last analysis these two are the same but we 

 shall discuss them separately. 



The mechanical theory never did have high standing with think- 

 ing men, and but for the support of a few leading physicists hav- 

 ing mechanical minds, would never perhaps have been developed 

 beyond a mere tentative hypothesis. We have no reason to think 

 that even Lord Kelvin himself, chief exponent of the mechanical 

 theory, ever considered it more than such a working hypothesis. 



We are all familiar with the character and properties assigned 

 to the mechanical ether; its enormous elasticity and infinitesimal 

 density to give the proper value to the velocity of light, its enor- 

 mous tensile strength to support gravitational forces, its solid prop- 

 erties to propagate transverse light waves, its fluid properties to 

 permit heavenly bodies to move through it with fixed velocities, 

 and so on. The mechanical ether reached its highest develop- 

 ment as a vortex sponge at the close of the last century. It has 

 passed away, not by violence but by starvation. It always was 

 a monstrosity and we are only too glad to be able to discard it 

 forever. 



The stubborn refusal of all phenomena, both natural and arti- 

 ficial, to show any indication of absolute motion in space has no 

 direct bearing on the question of the existence of an electromag- 

 netic ether. The Lorenz contraction hypothesis, with the elec- 

 tron theory of matter, offers us one loophole of escape from the 

 stubborn facts, the relativity theory several. It is too early to 

 say what will be the outcome, into what framework of theory, our 

 experimental facts will fit with least violence to themselves. 



Some relativists would have us reject the ether entirely on the 

 ground that it is useless. I, myself, fail to see how it can be dis- 

 pensed with, any more than atoms or molecules can be dispensed 

 with, nor how anyone, at all versed in theoretical optics or elec- 

 tricity, can consider it unnecessary. 



In short, the mechanical ether of Kelvin, Lodge and Helm- 

 holtz, the ether most of us were brought up on, has been proven 



