132 



MR. G. W. C. KAYE ON THE 



It will be noticed that the nearer the atomic weight of the radiator is to that of 

 copper, the more marked and extensive is the maximum. 



The higher the atomic weight, the thicker is the screen at which the peak of the 

 curve occurs. The diagram provides a good indication of the amount of radiation 

 specially penetrating to copper which is present in each case. The resemblance 

 between the radiations from nickel and copper, especially for the thinner screens, is 

 noticeable. The case of silver is interesting. As mentioned above, its surface became 



too 



BOOSc. 



THICKNESS or PT SCREEN- 



"OOIO 



OOI5 



O020 



'0025 



Fig. 5. Pt screen, 28,000 volts. 



amalgamated, and hence its radiation could be expected to show features indicative of 

 both silver and mercury. This is the explanation of why the graph shows a first 

 weak maximum, due to silver, and afterwards rises again owing to the presence of 

 the mercury. 



With the thickest copper screens there is every indication that, just as with screens 

 of aluminium, the relative values for the penetrating radiations eventually follow the 

 order of the atomic weights of the radiators, though even with the thickest screens 

 tried the value for the copper radiation is still distinctly relatively higher than with 

 the aluminium screens.* 



* This gradual dying away of the selective transmission, as the rays increase in hardness, is in 

 accordance with the behaviour of the y rays, which ignore atomic structure. 



