812 Mr. A. B. Wood and Dr. W. Makower on the 



silver halide, so that no photographic action can be expected 

 In order to overcome this difficulty experiments were made 

 by Wood and Steven * to detect photographically the recoil 

 stream from polonium by means of Schumann plates, in which 

 the amount of gelatin is reduced to a minimum. This attempt 

 was unsuccessful ; but the failure to obtain any photographic 

 record may well have been due to one or both of the following- 

 causes. The experiments were performed by allowing a con- 

 fined beam of the recoil stream and a radiation from polonium 

 to pass through a strong magnetic field, and it was hoped 

 thus to separate the recoil stream from the a rays; but unless 

 the recoil particles and u particles carry different charges, 

 it is of course impossible to do this. There is, however, no 

 evidence to indicate what charge is carried by a particle of 

 radium G recoiling from polonium when it disintegrates, 

 unless it be justifiable to argue from the analogy of the 

 recoil of radium B from radium A, in which case the recoil 

 particle carries a single charge in contact w 7 ith the double 

 charge carried by the a particle. But even if it were possible 

 to separate the recoil stream from the a. rays by means of a 

 magnetic field, it seems doubtful whether any photographic 

 action could be expected with the sources of polonium 

 available except with an exposure of prohibitive duration. 

 Further experiments therefore seemed desirable. 



In order to obtain as strong a source of radiation as 

 possible, a length of about one centimetre of platinum wire 

 *14 mm. in diameter was exposed in a fine capillary tube to 

 about 300 millicuries of radium emanation which had been 

 reduced to a sufficiently small volume by condensation in 

 liquid air. After an exposure of three hours the emanation 

 w r as pumped out of the capillary, and the wire removed and 

 subsequently mounted in the apparatus used by Walmsley 







Fi 



g-i- 









(I 



,s 







L---- 





6 ' 







1 



| 





'4 





j- ** 



and Makower to measure the magnetic deflexion of the 

 recoil stream from radium Af. The arrangement is shown 

 in fig. 1, which is reproduced from the paper just quoted. 



* Wood and Steven, Proc. Phys. Soc. 27th April 1915. 



t Loc. cit. 



