Secondary X-rays and Electromagnetic Pulse Theory. 211 



The distribution in both cases is shown graphically in 

 fig. 4, where OA represents the direction of propagation of 



Fig-. 4. 



The outer curve shows the theoretical distribution of scattered X-radia- 

 tion-, the inner curve shows the distribution of fluorescent X-radiation; 

 observations are indicated by small circles and duplicated by crosses as 

 symmetry on the two sides was proved on a number of directions. 



the primary radiation, and the vector OP represents the 

 intensity of radiation in the direction OP. The outer curve 

 shows the theoretical distribution of the scattered radiation. 

 The inner curve, a circle, exhibits the uniform distribution 

 of the homogeneous secondary (fluorescent) X-radiation. 

 The actual observations are denoted by the positions of the 

 small circles. The crosses merely duplicate the actual 

 observations, as the two sides were found by a number of 

 experiments to be similar. 



It will be observed that only a few observations were 

 actually taken on one side of the primary beam, these being 



77" 



compared with the position a = — — . The equality in the 



intensities of the secondary scattered rays making equal 

 angles on the two sides of the primary beam has been shown 

 by one of the writers in a previous paper*. It was also 

 found to be the case with the homogeneous (fluorescent) 

 X-radiation from copper. 



It should be pointed out that it was only by using a soft 

 primary beam that thi 6 * theoretical distribution was obtained 

 in the case of the scattered radiation. 



It has been previously shown by one of us that under other 



* Phil. Trans. A. vol. cciv. 1905, pp. 467-479, 



