194 



PROFESSOR E. RUTHERFORD ON THE 



The second column gives the observed activity (measured by means of an 

 electroscope) for a long exposure of 24 hours in the presence of the emanation. 



In cases where a steady current of air is drawn over the active body, the observed 

 values are slightly lower than the theoretical. This is probably due to a slight 

 volatility of the product radium B at ordinary temperatures. 



18. a-Ray Curves. The analysis of the decay curves of the excited activity ot 

 radium, measured by the rays, will now be discussed. The following table shows the 

 variation of the intensity of the radiation after a long exposure in the presence of the 



K1O 



IO 



20 



30 40 



Time in Minutes. 



Fig. 12. 



radium emanation. A platinum plate was made active by exposure ol several days 

 in a glass tube containing a large quantity of emanation. The active platinum after 

 removal was placed on the lower of two parallel insulated lead plates, and a saturating 

 electromotive force of 600 volts was applied. The ionization current was sufficiently 



