MATTER, SPACE, AND TIME 



227 



station, the carrier wave is caught by the aerial 

 wire, and passed through a thermionic valve, which 

 rectifies it, and a telephone, which reproduces the 

 interruptions and variations of the rectified wave 

 as audible sounds. 



If we accept the view that an atom is composed 

 of corpuscles or electrons spaced round a nucleus, 

 the electro-magnetic radiation which constitutes 

 light, if it be emitted in accordance with ordinary- 

 dynamical principles, 

 might naturally be ^ 



supposed to take its 

 rise from the ac- 

 celerations of these 

 corpuscles as they 

 revolve in their or- 

 bits, though, as we 

 shall see later, this 

 view has not pre- 

 vailed in its simple 

 form. 



Faraday's con- 

 ception of tubes of 

 electric force, may 

 here be revived in order to explain the radiation 

 of light on the hypothesis of electronic accelera- 

 tion. As long as an electron is moving forward 

 with uniform velocity, it carries its attendant 

 tubes with it in a steady manner, and no radia- 

 tion occurs. When it is stopped suddenly, as 

 at the point O in Fig. 36, an electro-magnetic pulse 

 spreads out from it, travelling with the velocity of 

 light. Within the sphere covered by this pulse, 

 a tube of force such as 0/ is stopped, so as to 



Fig. ^6. 



