H. A. Bamstead — Atmospheric Radio-activity . 3 



was unmistakable and is clearly shown in the curves plotted 

 in Hg. 1. The upper and lower curves, I and III, represent 

 the decay of the activity of wires exposed in the open air on 

 different days, while the curve between them, II, was obtained 

 with a wire which had been exposed in a two-liter flask con- 



taining very weak radium emanation for the same time (3 

 hours), and charged to the same negative potential by means 

 of the Wimshurst machine. The resemblance is obvious, 

 especially in the initial rapid rate of decay, which is charac- 

 teristic of the radium-excited activity, and which I have never 

 failed to observe with the open-air wire when two or three 

 observations were taken within the first ten minutes after the 

 exposure ceased. When, however, the observations are care- 

 fully compared, it is evident that they do not entirely agree 

 within the limits of experimental error ; indeed a mere inspec- 

 tion of the curves in fig. 1 shows that, toward the end, the air 

 wires were falling off at a slightly slower rate than the one 

 exposed to radium emanation. It seemed probable that this 



