Ront gen Radiation from Vapours. 451 



small part of the incident primary being sufficiently pene- 

 trating to excite the characteristic iodine radiation. This 

 combined with the fact that hard rays do not ionize to any 

 large extent made the times of observation much longer than 

 in the other case. 



Radiation from Vapour of Methyl Iodide. 

 (Time of observation 15 to 20 minutes.) 



Percentage absorption by Al 



previous to absorption in 



column II. 



Percentage absorption by Al 



('0377 cm.) after absorption 



in column I. 



22 



39 



52 



21-6 

 20-8 

 22-5 



Mean value 



21-6 



2-3. 



A plate of solid iodine was constructed and the radiation 

 from it examined in the same manner as the bromide plate, 

 with the following results : — 



Radiation from Solid Iodine. 



Percentage absorption by Al 



previous to absorption in 



column II. 



Percentage absorption by Al 



("0377 cm.) after absorption 



in column I. 



22 



39 



52 



20-3 

 21-7 

 20-7 



Mean value 



20-9 



= 2-3. 



Again, the value of —for the solid and vapour was the 



