of a particles from various Radioactive Substances. 615 



In fig. 2 the curves for air obtained with different sub- 

 stances are given. The abscissae give the pressure in 



56 cms. 

 Pressui-e 

 centimetres of mercury, and for convenience also the cor- 

 responding ranges reduced to 76 cm. pressure and 15° 

 centigrade are marked. The ordinatea give the ionization 

 current measured by the electrometer for each particular 



2 82 



