Mr. Norman Campbell on Delta Rays. 



291 



should be said about the columns marked " corrected " in 

 Table V. It seemed clear in these observations that there 

 was an error in the apparent zero. Accordingly, the results 

 were corrected by taking as zero the point midway between 

 the extreme values obtained for V= ±40. When this cor- 

 rectiou is made the values for one leaf and two leaves coincide 

 very closely, 



The results are of the same nature as those obtained with 

 aluminium. There appears to be no difference in quality 

 between the incidence and emergence radiations. For the 

 thin layers of gold and silver the amounts of the two radia- 

 tions appear to be equal, while for the thicker copper leaf 

 the incidence is notably larger than the emergence radiation. 

 It is of great interest to compare the quality of the radiations 

 from the four metals used ; for this purpose the " mean " 

 curves of the sums of the positive and negative ordinates are 

 plotted in nV. 3. 

 V ° Fig. 3. 



It will be observed that the rays from the silver and gold 

 appear to be uniformly faster than those from the aluminium: 



U2 



