-f H. A. Bumstead — Atmospheric Radio-activity. 



might be due to the presence of a small proportion of some 

 form of activity decaying more slowly than that due to radium, 

 and which would, therefore, show itself in a more and more 



marked manner as time went on. Accordingly, wires 30 meters 

 long were exposed in the same manner and observations car- 

 ried on for four hours. The results of two such experiments 

 are plotted in fig. 2, in which, for greater clearness, the nat- 



