CLASSICAL AND NEW MECHANICS 183 



We are, at present, in the condition of this man. As we 

 improve in our ability to measure the velocity of light 

 under different conditions we shall, Professor Ein- 

 stein thinks, get closer to the knowledge of the abso- 

 lute V and to the relations for space and time which 

 he has derived. But we may suppose men will some 

 day find a kind of radiation which has a velocity 

 greater than V (for example, the transmission of 

 gravitation), and by its aid remove the conviction re- 

 maining in our minds that motion affects length and 

 time. Calculation may show that material bodies can- 

 not attain this velocity, but we are speaking of an 

 immaterial radiation. To say that such a radiation is 

 impossible is as futile, at least as unscientific, as for a 

 race of the blind to say that there is no light. 



Since the motion of any ponderable body is too slow 

 to make the ratio r /v an appreciable quantity, the only 

 supposable case, where this ratio can enter as a deter- 

 mining factor, is in problems of radio-activity and the 

 discharge of electricity through gases. In these, the 

 particles of matter are supposed to be so small and to 

 have a velocity so great that their mass and size are 

 measurable functions of their velocity. But to limit 

 the applicability of the principle of relativity to such 

 supposititious bodies as electrons, is to rob it of its im- 

 portance, and we should hardly consider it one of the 

 great principles of nature. 



But even this is not all: if we wish to apply the 



