310 Sir J. J. Thomson on a 1 lieory of 



more energy radiated in front o£ the plane than behind. 

 When the electric field of the corpuscle is confined to a 

 small cone we see that all the energy radiated is in front 

 of the plane, whatever may be the velocity of the corpuscle. 

 When the rays pass through a region in which there are 

 free corpuscles they tend to make the corpuscles move in 

 the same direction as those which produced the rays. 



Radiation from a corpuscle ivhose motion is being accelerated. 



We can easily adapt the preceding investigation to the 

 case when the velocity of the corpuscle is changing gradually. 

 If the velocity changes by Sv in the time t, then the investi- 

 gation just given shows that there will be a kink in the tube 

 of force carrying an amount of energy equal to 



2_Tre 2 (Bit) 2 



CO C 5 T 



Now hii/r is equal to the acceleration of the corpuscle ; 

 hence the energy travelling outwards along the tube of force 

 is equal to 



when /is the acceleration of the corpuscle. 



This energy takes a time t to leave the corpuscle. Hence 

 the rate at which the energy is radiated from the corpuscle 

 is equal to 



2ire 2 f2 

 <oc? J ' 



This expression is of the same form as when the lines of force 

 are uniformly distributed round the corpuscle. In the latter 

 case, however, the radiation spreads out in all directions in 

 space, while in the case we are considering it is all concen- 

 trated along the tube of force attached to the corpuscle. In 

 the former case we have the uniform distribution of energy 

 usually associated with the wave theory of light, while in 

 the case we are considering the energy is concentrated in a 

 manner more comparable with the emission theory, for the 

 energy is concentrated in a single system — the tube of force 

 attached to the corpuscle which is thrown into transverse 

 vibrations by the movement of the corpuscle. 



Regarding light as arising from the vibrations of corpuscles 

 and charges of positive electricity, we see that on this view 

 we should have transverse vibrations travelling along some, 

 but only some, of the tubes of electric force which pass 

 through the space surrounding the luminous body. The 



