ADAMS. — TRANSMISSION OF RONTGEN RAYS. 



687 



Table V contains the data of the experiment with ahnninium in full, 

 and in Table VI the mean ratios of transmission for that experiment 

 are collected. Table Vll gives the mean ratios of transmission for the 

 experiment with copper. The accuracy of the readings with aluminium 

 was greater than that of the readings with copper, the deflections being 

 larger. It is to be noted, however, in both Table VI and Table VII, that 

 the ratios for solid screens are not strictly comparable with the corre- 

 sponding ratios for laminated screens, for corresponding screens of the 

 two sets are not quite of the same thickness in most cases. In plotting 

 the curves in Figure 5, this fact is taken into account. 



TABLE VII. 

 Summary of Experiment ox Effect of Strfaces of Copper Screex. 



From the.se results we may conclude that in the case of aluminium 

 and of copper, the effect of the surfaces as such on the tran.smission of 

 the rays is too small to be detected in measurements of this degree 

 of precision, if it exists at all. 



4. Effect of Transmission through a Screen of One Metal on 

 Penetrating Power for a Screen of Another Metal. 



It has been generally supposed that the transmission of a beam of 

 rays through a screen of any substance renders the beam more pene- 

 trating toward another screen of the same or of any other substance 

 than it was originally. In view of the importance of this matter a re- 

 examination of the experimental facts seemed desirable. Accordingly 

 experiments were performed for the purpose of comparing the penetrating 

 power for a given metallic screen of rays direct from the tube with the 

 penetrating power for the same screen of rays which have passed through 

 a screen of some other metal. The ratios of transmission were used as 

 a basis of comparison. With most metals it was found to be true that 

 the ratio of transmission for a given screen was greater when the rays 



