138 G. F. BECKER RELATIONS OF RADIOACTIVITY TO COSMOGONY 



of radioactivity material. A fortiori, soil and rocks must possess such a 

 coating and also, so far as they are porous, a radioactive lining."* Pio- 

 neers in the study of the distribution of radioactivity were Messrs Elster 

 and Geitel,"^ who have shown that radium is particularly abundant in 

 clays and spring deposits. As has been mentioned, even volcanic matter, 

 especially the porous tuffs, contain some radium, while fresh lavas contaLi 

 little or none. In 1906 Mr E. J. Strutt made a very valuable series of 

 determinations of the activity of massive rocks, meteorites, and sedimen- 

 tary strata.*"* This investigation shows that granites and syenites are 

 much more radioactive than other rocks, although some granites — for 

 instance, that from the isle of Eum — contain very little radium. The 

 metallic meteorites show no sensible activity, and stony meteorites only 

 about as much as the basalts — a sixth or an eighth of that shown by the 

 more active granular rocks. Messrs Eve and Mcintosh ®^ have added a 

 number of American rocks to Mr Strutt's list and have corrected his 

 results by means of an improved ratio between the quantities of uranium 

 and radium existing in substances which are in radioactive equilibrium.** 

 The corrected averages for Mr Strutt's igneous and sedimentary rocks are 

 1.7 X 10~^^ and 1.1 x 10~'^ or in mean 1.4 X 10~'^ grams radium per 

 gram of rock. 



It is evident that the radioactivity of rocks must tend to raise their 

 temperature and to increase any temperature gradient which they might 

 have were radium absent. This was first pointed out in 1893 by Mr F. 

 Himstedt.*^ In the next year Mr Eutherford "" showed that the amount 

 of heat indicated by Messrs Elster and Geitels' determinations of the 

 radioactivity of soils far exceeded the average amount lost by the earth 

 through radiation. In the same year Mr C. Liebenow ^^ reached the 

 same result independently and inferred that radium, or at least the dis- 

 integration of radium, must be confined to small depths, since otherwise 

 the earth would be growing hotter. Within this shell the temperature 

 would be constant if all the heat were due to radioactivity. 



"* See J. Danne on superficial occurrences of radium ; Comptes Rendus, Paris, vol. 

 140, 1905, p. 241, and McCoy and Ross, American Chemical Society, vol. 29, 1907, p. 

 1702. 



«5 Phys. Zeltsch., vol. 3, 1902, p. 574 ; vol. 4, 1902, p. 162 ; vol. 5. 1904, p. 321. 



"o Proceedings of the Royal Society of London, series A, vol. 77, 1906, p. 472, and 

 vol. 78, 1906, p. 150. 



<" Philosophical Magazine, vol. 14, 1907, p. 23. 



"» Rutherford and Boltwood found that the amount of radium associated with 1 

 gram of uranium during radioactive equilibrium is approximately 3.8 x 10 — ' gram. 

 American Journal of Science, vol. 172, 1906, p. 1. See also A. S. Eve, ibid., p. 4. Mr 

 Strutt's paper was read before the appearance of this corrected ratio. 



«»Verhand. Freiburg, nat. Ges., vol. 14, 1903, p. 186, and Phvs. Zeltsch., vol. 5, 1904, 

 p. 210. 



'» Radioactivity, 1904, p. 344. 



"Phys. Zeltsch., vol. 5, 1904, p. 625. 



