698 



SCIENCE 



[N. S. Vol. XXVIII. No. 725 



less outflow of energy attending the events 

 proceeding within the atomic systems. 



Although the term "ceaseless" is justi- 

 fied in comparison with our own span of 

 existence, the radium clock will in point of 

 fact run down, and the heat outflow 

 gradually diminish. Next year there will 

 be less energy forthcoming to drive the 

 clock, and less heat given off by the radium 

 by about the one three-thousandth part of 

 what now are evolved. As geologists ac- 

 customed to deal with millions of years, we 

 must conclude that these actions, so far 

 from being ceaseless, are ephemeral indeed, 

 and that if importance is to be ascribed to 

 radium as a geological agent, we must seek 

 to find if the radium now perishing off the 

 earth is not made good by some more en- 

 duriagly active substance. 



That uranium is the primary source of 

 supply can not be regarded as a matter of 

 inference only. The recent discovery of 

 ionium by Boltwood serves to link uranium 

 and radium, and explains why it was that 

 those who sought for radium as the im- 

 mediate offspring of uranium found the 

 latter apparently unproductive, the actual 

 relation of uranium to radium being that of 

 grandparent. But even were we without 

 this connected knowledge, the fact of the 

 invariable occurrence in nature of these 

 elements, not only in association but in a 

 quantitative relationship, can only be ex- 

 plained on a genetic connection between the 

 two. This evidence, mainly due to the 

 work of Boltwood, when examined in de- 

 tail, becomes overwhelmingly convincing. 



Thus it is to uranium that we look for 

 the continuance of the supplies of radium. 

 In it we find an all but eternal source. The 

 fraction of this substance which decays 

 each year, or, rather, is transformed to a 

 lower atomic weight, is measured in tens of 

 thousands of miUionths; so that the uran- 

 ium of the earth one hundred million years 



ago was hardly more than one per cent, 

 greater in mass than it is to-day. 



As radio-active investigations became 

 more refined and extended, it was dis- 

 covered that radium was widely diffused 

 over the earth. The emanation of it was 

 obtained from the atmosphere, from the 

 soil, from caves. It was extracted from 

 well waters. Radium was found in brick- 

 earths, and everywhere in rocks containing 

 the least trace of demonstrable uranium, 

 and Eutherford calculated that a quantity 

 of radium so minute as 4.6 X 10"^* grams 

 per gram of the earth's mass would com- 

 pensate for all the heat now passing out 

 through its surface as determined by the 

 average temperature gradient. In 1906 

 the Hon. R. J. Strutt, to whom geology 

 owes so much, not only here but in other 

 lines of advance, was able to announce, 

 from a systematic examination of rocks and 

 minerals from various parts of the world, 

 that the average quantity of radium per 

 gram was many times in excess of what 

 Rutherford estimated as adequate to ac- 

 count for terrestrial heat-loss. The only 

 inference possible was that the surface 

 radium was not an indication of what was 

 distributed throughout the mass of the 

 earth, and, as you all know, Strutt sug- 

 gested a world deriving its internal tem- 

 perature from a radium jacket some 45 

 miles in thickness, the interior being free 

 from radium.^ 



My own experimental work, begun in 

 1904, was laid aside till after Mr. Strutt 's 

 paper had appeared, and valued cor- 

 respondence with its distinguished author 

 was permitted to me. This address will be 

 concerned with the application of my re- 

 sults to questions of geological dynamics. 



Did time permit I would, indeed, like to 

 dwell for a little on the practical aspect of 

 measurements as yet so little used or under- 



'Proo. R. 8., LXXVII., p. 472, and LXXVIII., 

 p. 150. 



