CLASSICAL AND NEW MECHANICS 179 



mental proof and the other factor, the length, is not, as 

 we cannot experiment on the path of light in free space. 

 But passing this objection, we have calculated from 

 length and time determinations a value for V and Pro- 

 fessor Einstein declares it to be an absolute constant. 

 He then reasons backward that the length of a body 

 and time determinations must be variables with motion, 

 in order to keep V constant. Of course, if Professor 

 Einstein wishes to look on the universe as a purely ab- 

 stract conception; and if he wishes to make what we 

 sometimes call concrete or objective phenomena cor- 

 respond to his preconceived idea of the universe, he 

 can assume V in a vacuum to be a universal and ab- 

 solute constant and no one can disprove it sci- 

 entifically. But there are some who still cling to 

 the idea that dimensions of bodies and time are 

 not subject to our fancy, and who believe that 

 if any quantities must vary, it should be those 

 which we have no means of determining directly. 

 And after all it is asking a great deal of us, to 

 upset our ideas in order to explain at bottom a 

 single experiment, that of Michelson and Morley, how- 

 ever accurately it has been performed and however 

 puzzling its results may be. He has not even the 

 justification his predecessors would have had. When 

 the ether was believed to be a crystalline solid which 

 vibrated with the passage of light rays, V had a real 

 meaning although we could not determine it directly. 



