1898.] Reflection of Rontgen Rays. 395 



impulsive velocity be w. The magnetic force in the secondary 

 pulse will in a direction making an angle ty with the axis of z and 

 at a distance r from the particle be equal to 



— Vl — sin 2 i/r sin 2 <£, 

 ar ' 



while the energy in the pulse will be proportional to 

 — — (1 — sin 2 ylr sin 2 <f>). 



Let us suppose that instead of there being only one ray there 

 are a large number in which the electric intensity is in different 

 directions, but uniformly distributed round z, then the energy will 

 be proportional to 



^(l-*sin^), 



thus the energy when -v/r = .0 or tt is twice that when -^r = 7r/2. So 

 that if the secondary radiation arises solely from an action of this 

 kind the intensity of the reflected radiation in the direction of the 

 primary rays would be twice that in a direction at right angles 

 to them. 



The intensity of the diffuse reflection in different directions 

 was tested by the following method. A BCD is a box made of 



EHM B 



Fm. 1. 



sheet lead, Rontgen rays pass into this through a small lead tube 

 EFGH and are diffusely returned from the patch KL\ pieces of 

 photographic plates with screens of perforated zinc in front of 

 them were placed at M and N, at equal distances from the middle 

 of the patch HK ; the diffusely returned rays from HK produced 

 after an exposure of about two hours photographs on the plates 

 N, M; the photographs at M and N did not show any appreciable 

 difference in intensity though a large series were taken with 

 exposures varying from 2 to 6 hours. Tests were made which 

 showed that these photographs were made by rays coming from 

 HK and not from the air through which the primary Rontgen 

 rays passed. This was done by removing the bottom of the box, 

 when the effect on the plates was very slight compared with that 

 produced when the bottom of the box was in its place. Though 

 the photographic method is not a very delicate test of the relative 



