Secondary Réntgen Radiation. 553 
The solid angle subtended by this aperture at the centre 
of the source of secondary 1 ‘adiation distant about 18°5 cm. 
was approximately 
52 1\2- 
(185)? be cesateae 
Evidence was given ina previous paper leading to the theory 
that this radiation has its origin in the charged corpuscles 
constituting the molecules during the passage of X-rays 
through the gas. The perturbations of these charged cor- 
puscles by the strong electric field in the Réntgen pulses are 
in directions perpendicular to that of propagation of the 
primary rays, and the intensity of secondary radiation pro- 
ceeding from a single corpuscle is different in different 
oD 
directions, being expressed by 
Ley sie @ ». 
Agra Neri © 
e being the charge on the corpuscle, f the acceleration of that 
corpuscle, V the velocity of light, * the distance of the point 
considered from the corpuscle, and 6 the angle between the 
line joining these two with the direction of acceleration of the 
corpuscle, 
The rate at which?energy is radiated from the corpuscle is 
9 o2f2 
a 
Consequently the energy received by a small area sub- 
tending a solid angle w’ at the corpuscle = 
3 
"sin? 6 of the total energy of secondary 


radiation proceeding from that corpuscle. 
Now, as the electric displacements in the Réntgen radiation 
are in all directions perpendicular to the direction of pro- 
pagation, and neglecting partial polarization of the primary 
beam t, if the line joining the small area to the source 
of secondary radiation be in the plane of electric displace- 
ments, the energy received by this area= 
! 
ae es of the total energy of secondary radiation 
Tr 
proceeding from that corpuscle (the average of sin* @ being 4). 
* J. J. Thomson, ‘ Conduction of Electricity through Gases,’ p- 269. 
her. , 
+ Through an error in integration this 1s given as > 3 V in ‘Conduction 
of Electricity through Gases.’ 
t C. G. Barkla, Nature, March 17, 1904. 
