158 THE LIMITATIONS OF SCIENCE 



connected with light and electricity became pressing. 

 Of these, three stand out most prominently. 



The phenomena associated with electricity when it 

 passes through very high vacua and with radio-active 

 bodies like radium are now explained as being due to 

 the action of excessively small particles, carrying a 

 charge of electricity and moving with a velocity com- 

 parable to the velocity of light, or about one hundred 

 thousand miles per second. These particles, both be- 

 cause of their smallness and because of their velocity, 

 are in an entirely different class from the bodies 

 previously considered in mechanics which have a sen- 

 sible mass and whose greatest velocity is less than one 

 hundred miles per second. Errors in mechanical laws 

 which would otherwise be inappreciable may easily 

 assume large proportions when applied to such ex- 

 treme cases. The hypothesis of the electron has 

 profoundly modified the conception of the atom, and 

 the nature of matter and motion. 



In the second place, recent experiments lead to the 

 belief that matter is always electrified; that light is 

 due to electrical variations; and that the amount of 

 electricity associated with a given amount of matter is 

 a fixed and invariable quantity. It is further shown 

 by theory and confirmed by experiment that if an 

 electrified body be moved, the ratio of its electrical 

 charge to its apparent mass must vary with the velocity 

 of its motion; and since the electrical charge is assumed 



