Secondary <y Radiation. ,363' 



mercury, cadmium, and zinc correspond to the system 

 of electric vibrations which is most easily set up in the atoms 

 of these three elements. This would lit in with the view 

 expressed by Stark that the lines of these three series are the 

 ones which correspond to atoms of mercury, cadmium, and 

 zinc in the neutral state. 



In conclusion I desire to thank my assistant, Mr. P. 

 Blackmail, for his help in taking the photographs. 



Description of photograph reproduced in Fig. 1, Plate VI. 



This photograph shows the spark spectrum of zinc in air in the ultra- 

 violet region and the absorption hand at X 2139-83. In the second 

 spectrogram of the reproduction the band is narrow, and sharply edged, 

 while in the third it is of considerable width. 



XLIV. Secondary y Radiation. By D. C. H. Florance, 

 M.A , M.Sc, Assistant Lecturer and Demonstrator, 

 University of Manchester *. 



IT has recently been shown t by the writer that 7 ray& 

 emitted from radium C in traversing thin .sheets of lead 

 give rise to a complex secondary radiation. This radiation 

 consists of a scattered radiation similar in type to that 

 emitted by elements of low atomic weight, together with 

 a softer radiation probably characi eristic of lead. The 

 amount of this combined radiation is greater than that 

 emitted from a radiator of low atomic weight such as zinc, 

 in which case the secondary radiation consists simply of the 

 scattered radiation. From these experiments, it seemed 

 probable that there existed some definite relation between 

 the amount of secondary radiation emitted from different 

 radiators and the atomic weights of the radiators. This 

 conclusion was, moreover, supported by the results obtained 

 in an earlier paper J, when it was found that the purely 

 scattered radiation was the same in type for all radiators, 

 and that the differences generally observed were due to the 

 experimental conditions. Gray§, by allowing for the ab- 

 sorption of the scattered radiation, concluded that the 

 quantity of scattered radiation was approximately inde- 

 pendent of the radiator. Further experiments have now 

 been made, using equal masses of thin radiators, so that 

 the absorption of the scattered radiation in the radiator was 

 comparatively small. 



* Communicated bv Sir Ernest Kutherford, F.B.S. 

 t Florance, Phil. Mag. Feb. 1914. 

 t Florance, Phil. Mag. Dec. 1910. 

 § Giav, Phil. Mag. Oct, 1913. 



