of Narrow X-ray Beams. 391 



case of the '6 mm. The methyl iodide had always an effect 

 on the insulation even when the gas mixture was well dried*. 

 The plane angle of rays entering the ionization chamber 

 Fig. 1. — Log Absorption Curves of X-rays. 

 7. 



1 

 Log I 



0^ 

 o 



in the wide-angle beam was 13°. The rays fell also on the 

 sides of the absorption chamber, but a check experiment, in 

 which the beam was limited by a lead screen so that it just 



* Amber, sealing-wax, and rubber are attacked by the iodide ; the 

 insulation of quartz was impaired ; quartz coated with sulphur answered 

 fairly well but was affected — it recovered if S0 2 was passed through. 



