374 Prof. E. Rutherford and Mr. F. Soddy on 



velocity approaching that of light. But thorium, in com- 

 parison with uranium and radium, emits a much smaller 

 proportion of deviable radiation. The determination of the 

 proportion between the deviable and non-deviable rays 

 aftords a new means of investigating thorium radioactivity. 



The electrometer thus supplies the study of radioactivity 

 with methods of quantitative and qualitative investigation, 

 and there is therefore no reason why the cause and nature 

 of the phenomenon should not be the subject of chemical 

 investigation. 



Fig. 1 shows the general arrangement. From 0*5 to 

 0*1 gram of the compound to be tested, reduced to fine 

 powder, is uniformly sifted over a platinum plate 36 sq. cms. 

 in area. 



Fig. 1. 



■£art/t- 



■ Earth. - 



£osfA. 



This plate was placed on a large metal plate connected to 

 one pole of a battery of 300 volts, the other pole of which 

 was earthed. An insulated parallel plate was placed about 

 6 cm. above it, and the whole apparatus inclosed in a metal 

 box connected to earth, to prevent electrostatic disturbance. 

 The shaded portions in the figure represented insulators. 

 A door was made in the apparatus so that the plate could be 

 rapidly placed in position or removed. Both pairs of quad- 

 rants are first connected to earth. On connecting the one 

 pair with the apparatus, the deflexion of the needle from zero 



