274 Prof. Barkla and Mr. Ay res on the Distribution of 



positions — as A and A' in fig. 3. A second electroscope was 

 used to standardize the intensity of the radiation in a fixed 



direction. As the distances in both carbon and air through 

 which the measured secondary radiations passed were the 

 same in the two positions, the ionizations observed were pro- 

 portional to the intensities of the radiation proceeding from 

 the atoms themselves, without subsequent absorption, in 

 these two directions. 



Taking the directions in pairs, the following results were 



obtained for the ratio y~, the suffix denoting the angle 



J-jt/2 



between the direction of propagation of the central primary 

 ray and the central secondary ray in each case. To deter- 

 mine the intensity in directions making angles 20, 30, and 

 40 degrees with the direction of primary radiation, the 

 secondary radiation from the face of emergence of the primary 

 beam was studied. In all other cases the radiation emerging 

 from the face of incidence was studied. 



The radiation scattered from the air was measured by 

 direct experiment, and correction was made for this in 

 determining the intensities of radiation from the carbon. 

 This correction was very small in all the experiments except 

 for the angles 20° and 30°. 



In Table I., column 1 gives the angle between the central 

 primary and central secondary rays ; 



Column 2 gives the theoretical values of the ratio 



Iff/2 



if 



the primary and secondary beams were narrow pencils co- 

 inciding with the axes of the beams actually experimented 

 upon ; 



