1908] on Radio-active Changes in the Earth. 153 



deep green colour ; but scientifically the distinction is of no impor- 

 tance. Some beryls contain enormously more helium than can be 

 accounted for by the small traces of radium in them. Nor do they 

 contain any appreciable quantity of other radio-active material. 

 What view, then, can we take of the presence of helium in this 

 mineral ? It is, to me at least, difficult to believe that the gas can 

 have been introduced from without. If not, can it have been 

 generated from radium formerly existing in the beryl, but now 

 exhausted ? This, too, seems unlikely, for it would imply that beryls 

 are older than other minerals, and there is no plausibility in such a 

 theory from the geological standpoint. My own opinion is that, in 

 all probability, an element hitherto unknown exists in the mineral, 

 from which the helium is generated. It may be objected that, in 

 that case, the mineral ought to be radio-active. If, however, the 

 radiation were emitted with less than the critical velocity, we should 

 not be able to detect it, and nothing is known to make such an 

 hypothesis improbable. 



In conclusion, I shall be well content if I have convinced you 

 that there is still something to be learnt from careful examination of 

 the most commonplace materials. If there is nothing new under the 

 isun, there are, at least, unsuspected things going on inside the earth, 

 where the sun cannot penetrate. 



[R. J. S.] 







^\ -mt.4»^!h:.- / Jew 



