﻿Deflexion of Recoil Stream from Radium A. 255 



on a frame which could be adjusted in any position within 

 the box; the photographic plate was also mounted on an 

 adjustable carrier. 



Fiar. 2 e 



J D 



L P 



The box was placed between the pole-pieces M of a large 

 electromagnet. The distance between the pole-pieces was 



I cm. and their face area 16 cm. x 5 cm. A current of 



II amperes gave a uniform field of about 15,000 gauss over 

 the whole area, so that throughout their paths the « rays 

 and recoil stream were in a uniformly strong magnetic field. 

 The whole of the glass apparatus near to the box was painted 

 black. The active source used consisted of radium A 

 collected on a platinum wire O'l mm. in diameter. This 

 fitted into a groove cut in the plate C. The groove was 

 adjusted until it was horizontal and parallel to the slit 8, 

 and reference marks were then placed in white paint on 

 the two parts of the joint B for simplicity in subsequent 

 adjustments. 



In order to insure a high efficiency of recoil, the wire was 

 made active with radium A in an apparatus similar to that 

 described by Wertenstein*, in which the wire could be 

 removed from the emanation without drawing it through 

 mercury. From 50 to 100 millicuries of emanation were 

 used, and the wire was exposed to the emanation for six 

 minutes. At the end of the exposure the wire was dropped 

 for a few seconds into a glass tube maintained at 100° C. to 

 remove emanation. The wire was then fixed in position in 

 the groove cut in the plate C (fig. 2) by means of a speck of 

 soft wax. The stopper B was then replaced and rotated 

 until the wire was horizontal and the magnetic field was 

 excited. These operations usually occupied 2 to 3 minutes. 

 The box was rapidly evacuated, first by means of a Fleuss 



* Theses presentees a la Faculty des Sciences, Paris, 1913, p. 90. 



