TIME AND MOTION 77 



the particles sent out from radium, which move 

 with a velocity near to that of light. 



The paradox suddenly appeared in the cele- 

 brated investigation of Michelson and Morley. 

 This set the mathematical physicists violently 

 at work, and it was pointed out by Fitzgerald 

 and by Lorentz that the paradox could be at 

 least temporarily avoided by assuming that all 

 material objects in motion are shortened in the 

 direction of their motion. The great work of 

 Lorentz, which was a masterly effort to express 

 all new data in terms of the existing theory, 

 really paved the way for the new theory which 

 was to replace it. He was obliged to assume 

 that, in addition to the universal time of New- 

 ton, each moving system has a separate time 

 system of its own, but it was Einstein who saw 

 that all of the enormous complexities which had 

 developed in kinematics could be swept away 

 by regarding any one of these local time sys- 

 tems as just as valid as any other, and thus 

 doing away with universal time. So far-reach- 

 ing were the results of this simple idea that the 

 same stroke of the eraser which wiped out uni- 

 versal time also wiped out universal ether. Ether 

 is left as a beautiful word which may again find 



