EMANATIONS. 115 



which it is to be remembered, is phosphorescent to the ac- 

 tion of radium rays, was placed in the other flask; then 

 both flasks were closed. So long as the cock between the 

 flasks remains closed, nothing is visible in the dark; but 

 the instant it is opened, the sulphide of zinc becomes bril- 

 liantly phosphorescent and continues so as long as the tube 

 connecting the flasks remains open. Now we cannot believe \ . 

 that either the alpha-, the beta- or the gamma-rays from 

 radium have the power to pass around a corner as they 

 would necessarily do in order to pass from flask to flask to 

 cause the zinc sulphide to phosphoresce. In fact we know && \*J1 

 they do not, and hence we must believe, for there is no 

 other way out of it, that a something more or less in the 

 nature of a gas, and not these rays at all, must pass from 

 flask to flask; and since, moreover, this something causes 

 the zinc sulphide to shine in the dark, we must also be- 

 lieve that it is radio-active. Now this radio-active some- 

 thing which passes out of radium and which is a some- 

 thing distinct and apart from the rays themselves has been 

 called an emanation. It is called an emanation rather 

 than a gas because Rutherford, its original discoverer, was 

 not sure that it was a gas. It is apparently the cause 

 of this induced radio-activity acquired by all bodies in the 

 neighbourhood of radium, for spreading out from the ra- 

 dium it settles on surrounding objects and renders them 

 radio-active. Having settled, then, the fact of a radio- 

 active something spreading out from radium independent 

 of the straight line radiations of the alpha-, beta- and 

 gamma-rays, it is of extreme importance to find out what 

 it is. Here, then, are some experiments, which one after 

 another elucidates, to some extent, the nature of the emana- 

 tion. 

 First, let us remember that whether it is a gas or not, it 



