304 MODERN SCIENCE READER 



ether; and that assumption, in Hooke's day, must have 

 been only a speculation. But it is the kind of speculation 

 which time is justifying it is the kind of truth which we 

 all feel to be in process of establishment now. 



We do not depend on that sort of argument, however; 

 what we depend on is experimental measure of the mass, 

 and mathematical estimate of the volume, of the electron. 

 For calculation shows that however the mass be accounted 

 'for, whether electrostatically or magnetically, or hydrody- 

 namically, the estimate of ratio of mass to effective volume 

 can differ only in a numerical coefficient and cannot differ 

 as regards order of magnitude. The only way out of this 

 conclusion would be the discovery that the negative electron 

 is not the real or the main matter-unit, but is only a sub- 

 sidiary ingredient, whereas the main mass is the more 

 bulky positive charge. That last hypothesis, however, is 

 at present too vague to be useful. Moreover, the mass of 

 such a charge would in that case be unexplained, and would 

 need a further step ; which would probably land us in 

 much the same sort of ethereal density as is involved in the 

 estimate which I have based on the more familiar and 

 tractable negative electron. 



It may be said, why assume any finite density for the 

 ether at all? Why not assume that, as it is infinitely con- 

 tinuous, so it is infinitely dense whatever that may mean 

 and that all its properties are infinite? 



This might be possible were it not for the velocity of 

 light. By transmitting waves at a finite and measurable 

 speed, the ether has given itself away, and has let in all the 

 possibilities of calculation and numerical statement. Its 

 properties are thereby exhibited as essentially finite how- 

 ever infinite the whole extent of it may turn out to be. 



