Fig. 2. 



Fig. i. 



Fig. 3. 



Fig. 4. 

 PLATE I. 



Fig. 1. — Alpha-rays from radium. 



Fig. 2. — Alpha-rays from radium : the a-particles all traversed the air after its expansion. 



Fig. 3. — Enlargement of portion of Fig. 2. 



Fig. 4. —Alpha-rays from radium emanation. 



[483 



