2 Makowek, Scattermg during Radio-active Recoil. 



the recoil-stream coming from the active wire P, coated 

 with radium A, but so that recoil-atoms reflected or 

 scattered from the copper reflector O could reach it. The 

 distance from the wire to the reflector O was 1*4 cms., 

 and that from the reflector to the surface V2 cms. After 

 an exposure of ten minutes in vacuo, the plate S was 

 removed and found to be active, and the nature of the 



\^ 



Fig. 2. 



active matter on the plate was ascertained by measuring 

 its rate of decay with an a-ray electroscope. After expos- 

 ing a plate for ten minutes to the radium B expelled from 

 the wire, the activity should at first rise and attain a 

 maximum after 27 minutes, and then fall ofl" with time aS 

 indicated by the dotted curve {Figure 2), which has been 



