The Recoil of Radium C from Radium B. 



101 



radium C from radium B without the interference of secondary 

 disturbances. 



Before discussing these conditions it will be necessary to 

 briefly describe the apparatus used and the method of con- 

 ducting an experiment, which were essentially similar to 

 those employed in the experiments quoted above. 



The glass vessel V (fig. 1), of 1*9 cms. diameter, was 



Fig. 1. 



provided with stoppers at both ends. A brass support A was 

 fixed as shown in the diagram, and an active plate P which 

 was to serve as the radiating surface could be placed upon it. 

 From the other stopper a disk was suspended by a wire and 

 exposed to the radiation from the plate mounted on A. After 

 an exposure of the required time with the air in V at the 

 desired pressure, the disk B could be removed and tested for 

 its activity in the usual manner, either by means of a 

 quadrant electrometer or a sensitive a ray electroscope. 



