Secondary X-raz/s and Electromagnetic Pulse Theory. 271 



proportion, and that where scattering occurs the scattered 

 radiation differs inappreciably in penetrating power from the 

 primary radiation, that is to say there is no appreciable 

 degradation accompanying the process of scattering. These 

 and other experimental results are in perfect agreement with 

 the theory of scattering, as first given by Sir J. J. Thomson. 



A further test was naturally suggested by the first three 

 of these results, — that of making a detailed investigation of 

 the distribution of the scattered X-radiation around the 

 radiating substance. 



The secondary Rontgen radiation which has been found 

 to proceed from light elements when traversed by a beam of 

 X-rays is such as would be produced by the acceleration of 

 electrons in the direction of electric force in the primary 

 pulses during their passage over these electrons. 



If the primary beam be nnpolarized, these accelerations 



are on the average uniformly distributed in direction over a 



plane perpendicular to the direction of propagation of the 



primary radiation. Each accelerated electron is the source 



of a radiation in which — assuming a uniform distribution of 



electric polarization — the electric force is given by the ex- 



fief sin 8 ~ , . .', , .., , 



pression , where e is the charge, j the acceleration 



of the electron, r the distance of the pulse from the origin, 

 /uu the permeability of the medium, and 3 the angle between 

 the direction of acceleration of the electron and that of 

 radiation considered. The intensity of radiation in any 

 direction is thus proportional to sin 2 /3. 



Thus if OA be the direction of propagation of a primary 

 pulse, OB and OC the directions of the electric and magnetic 



fields in the pulse, then an electron at is the source of a 

 radiation the intensity of which in any direction OP is 

 proportional to sin 2 FOB. 



* The uniform distribution of tubes of electric force around an electron 

 is, of course, not essential to the calculation. What is essential is the 

 transverse wave theory. 



