EMANATIONS. 119 



For the first question the answer is ready. The emana- 

 tion emits only alpha-rays, bodies positively electrified as 

 big as atoms. 



For the second question, the answer is also ready. The 

 radium from which the emanation has been extracted has 

 lost about seventy-five per cent, of its activity, and the rays 

 which it does still emit after the lapse of an hour or so are, 

 again, only alpha-rays. Leaving for the present the ques- 

 tion as to what becomes of the beta- and gamma-rays, we 

 are now face to face with possibly the most remarkable, the 

 most interesting and the most illuminating fact in connec- 

 tion with all this strange eventful history of the nature of 

 radium. We have said that the emanation abstracted from 

 the radium retained its ray-emitting power for some time. 

 The obvious inference is that it eventually loses its power 

 completely. It does. We have also said that the radium 

 from which the emanation has been abstracted, after the 

 lapse of an hour or so, loses seventy-five-per cent, of its ac- 

 tivity. This also is true. But wait a month, and the most 

 remarkable fact crops out that the radium, during the inter- 

 val, has restored all its lost emanation and has fully regained 

 its activity. The interesting phase of the fact lies in the 

 further discovery that the emanation abstracted from the radium 

 loses its radio-activity at the same rate and according to the 

 same laws as the de-emanated radium regains it. A perfectly 

 clear demonstration of this is given in the diagram (Fig. 39), 

 in which the curve A represents the actual rate of recovery 

 of the radium activity and curve B the rate of decay of the 

 radium emanation. The illuminating phase of the fact lies 

 in its inferences. If, as is apparently the case, the radium 

 is constantly generating and storing the emanation and the 

 emanation as constantly decaying, the activity of the radium 

 at any one time is due to a balance between the decaying 



