Rontgen Radiation in Air. 



605 



of this radiation, it seemed of interest to examine the 

 radiation from air more minutely, to ascertain whether the 

 incident radiation was perfectly scattered under all con- 

 ditions. 



The primary and secondary radiations were measured by 

 the ionization produced in two gold-leaf electroscopes. The 

 ordinary Cambridge type of electroscope was sufficiently 

 sensitive to measure the primary radiations, and a Wilson 

 tilting electroscope was tried for the secondary. This 

 instrument gave a deflexion of 80 divisions per volt, which 

 was not enough for the purposes of the experiment, and as 

 it was practically enclosed in a lead box, to prevent stray 

 radiations from reaching it, it was troublesome to adjust 

 when, as often happened, the leaf moved beyond the region 

 of stable equilibrium. 



A modification of the Wilson instrument was next tried 

 (fig. 1). The brass plate B was kept at 200 volts and 



could be moved to-and-fro by the ebonite handle H. When 

 the whole arrangement was in place and surrounded by 

 the lead box, with only the rod R and handle projecting, 

 the required degree of sensitiveness could be obtained by 

 gradually pushing the brass plate inwards. 



A word may here be said on the cutting of gold leaves. 

 The author has found the following method very successful. 

 Heat a pellet of paraffin wax on a clean glass plate to form 

 a thin film. While the film is still liquid take a square of 

 gold leaf, and gripping it along one edge between two 

 paper strips, allow the opposite edge to touch the film along 

 its whole length. Then the square is cautiously lowered so 



Phil. Mag. S. 6. Vol. 14. No. 83. Nov. 1907. " 2 S 



