Spectrum of Penetrating 7 Bays from Radium B and C. 265 



The following table gives the results of these experiments. 

 The wave-lengths have been deduced from the data given in 

 the previous paper. 



Table I. 



Penetrating 7 rays from radium B and radium C. 



Angle of reflexion 



Wave-length 



from rocksalt. 



in cms. 



44' 



•72xl0" 9 



B 1° 0' 



•99 



1° 11' 



116 



1° 24' 



1-37 



ri° 37';* 



A 11° 43' J 



1-59 

 1-69 



2° 0' 



1-96 



2° 28' 



2-42 



2° 40' 



2-62 



3° 0' 



2-96 



3° 18' t 



324 



40 , + 



393 



4° 22' 



4-28 



* The lines at 1° 37' and 1° 43' may possibly be one broad line, having a 

 mean reflexion angle of 1° 40'. The evidence, however, seems to be in favour 

 of the double nature of the line, which was by far the strongest line on most 

 photographs. We were for some time in doubt as to the existence of a line 

 reflected at 44', but its presence has been confirmed in several reflexion and 

 transmission (see p. 266 et seq.) photographs. 



t Possibly second orders. 



Of these lines, those marked A and B showed up strongly 

 on the photographic plate, A being the more intense. The 

 other lines were comparatively faint. In addition to those 

 recorded, which have been observed on Severn 1 plates, a 

 number of very faint lines have also been observed, but it 

 has not been thought desirable to include them. 



It is of importance to decide which of these lines belong 

 to radium B and which to radium C. To bring out this, 

 photographs taken with a screen of 6 mm. of lead between 

 the source and the crystal were compared with similar 

 photographs either with no absorbing screen, or with a 

 screen of aluminium 2 mm. thick between the source and 

 crystal. The latter absorbed the soft 7 rays from radium B 

 but did not stop more than a small percentage of the 

 penetrating rays. The lead plate, on the other hand, 

 practically cuts out the greater part of the radiations from 

 radium B, and no doubt also some of the softer possible 



