PRESIDENTS ADDRESS. 17 



conipounds spontaneously, and at a definite rate, yield radium, 

 which in turn breaks up, giving rise ultimately as its chief pro- 

 duct to the gas helium. 'J his latter substance was first detected 

 speotroscopically in the sun, but is now known to exist in small 

 amount in our atmosphere, in the water and gas emitted l)y 

 springs, and in a number of minerals. 



Opinions as to the precise nature of the phenomenon involved 

 in the disintegration of radium are at the present time somewhat 

 divided. The most generally held view is that we have here to 

 do with a true case of atomic disintegration, the actual breaking 

 up of a cliemical element through the disintegration of its atoms, 

 the integrity of which has hitherto been an axiom of chemistry. 

 This is the opinion expressed by such capable observers as the 

 Hon K.J. Strutt, Mr. Soddy and others, and, with some reserve, 

 by Prof. Rutherford. On the other hand, it is considered by the 

 veteran Lord Kelvin and by Prof. Armstrong that it may quite 

 well be that the emanations from uranium, and in turn from 

 radium, pre-exist as such, and are simpl}'^ continually escaping 

 from combination, that, in fact, radium ma}^ be merely a com- 

 pound body liberated from uranium and in turn breaking u\> 

 explosively. The contention of the latter authorities is that the 

 atomic disintegration theory is not proved and that speculation 

 has gone ahead of observation. This question, however, does not 

 particularly concern the aspect of the subject with which I desire 

 to deal on this occasion, so that its further discussion will not be 

 necessary here. 



I have already mentioned that the phenomenon wliich we have 

 been considering is accompanied by the liberation of a relatively 

 enormous amount of energy, the bulk of which makes itself 

 manifest as heat. Assuming that uranium (or other radium- 

 producing substance) is distributed in sufficient quantit3^through 

 the earth's crust and that the disintegration phenomena with 

 accompanying liberation of heat go on beneath, as thf'y do at the 

 surface, the production of this heat will have a most important 

 bearing on internal terrestrial temperature, on \olcanic activity, 

 and, incidentally^, on the great question of geological time. 



