Primary and Secondary 7 Rays. 

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Electroscope at an anple 55°. Comparison of amount of secondary 

 radiation for different thicknesses of different materials. 



Position I. The angle between the normal position and 



this position is approximately 25°. The carbon 



radiator produces more secondary radiation than does 



iron or lead. 



Position II. The angle is approximately 55°. In this 



case the curve for carbon has fallen below that for 



iron, and even after 12*5 cm. o£ carbon the maximum 



amount of secondary radiation had not been reached. 



Lead reaches its maximum value and then decreases. 



A quantitative relation between the amounts of secondary 



radiation emitted by different radiators was looked for, but 



no evidence of such a relation has been discovered. The 



absorbing action of the 6 mm. side of the electroscope would 



tend to mask any relation. It seemed probable, too, that 



variations in the amount of secondary radiation would bo 



produced according to the experimental arrangement. In 



the present case, the volume of a certain weight of lead 



differed greatly from a similar weight of carbon, 



This is borne out by the result of a special experiment. 

 For example, five sheets of lead were spaced out over a dis- 

 tance of 8 cm. They were held together by four thin brass 

 rods so that they could be easily suspended in position, and 



