RADIOACTIVE MATTER 457 



stop or reverse the process of radioactive decay ? So far as our 

 present knowledge goes, no change of conditions has any 

 appreciable effect on radioactive decay, but we are inclined to 

 forget the infinitesimal nature of such changes in proportion to 

 the colossal energy equivalent involved in intra-atomic change. 



" The great majority of ordinary chemical actions, especially 

 those which occur in nature, are not appreciably affected, and 

 are certainly not reversed, by a few degrees of temperature or 

 by a small change of pressure. The energy equivalent of 

 radioactive decay is, mass for mass, many thousand times 

 greater than that of the most violent chemical action, conse- 

 quently we are not entitled to infer the irreversibility of this 

 change until we are able to control changes of physical con- 

 ditions proportionately greater than those we commonly apply 

 to chemical reactions. 



" But, in the interior of the Earth, these plutonic conditions 

 actually exist. Mr. Clarence King has calculated that the 

 pressure would probably be measured in millions of atmo- 

 spheres, and Sir George Darwin has shown that theories of 

 tidal action necessitate the assumption that there is continual 

 addition to the heat stored in the interior. . . . The difficulties 

 are removed if we combine this idea of Dr. Barrell concerning 

 the origin of radioactive matter with the assumption of a very 

 slow convective action in the Earth's interior. It is not then 

 necessary to assume that radioactive substances are confined 

 to the Earth's surface, or that the interior of the Earth possesses 

 any colossal temperature. According to this hypothesis, when 

 conditions of temperature and pressure exceed a certain critical 

 amount, the energy will be stored metachemically, in the form 

 of radioactive compounds. As these find their way very slowly 

 to the surface, energy will be given off again in their slow 

 disintegration." ! 



After the lapse of several years, what is there to add to the 

 passage I have quoted ? There is very little of any moment. 

 The problem remains now very much as it did then. Quite 

 recently there had been a discussion in the columns of Nature, 

 in which Mr. Arthur Holmes and Dr. Schiller took part, but 



1 Sir George Darwin's paper is published in the Philosophical Transactions, 

 Series A, 1879; the passage in question is found on p. 592. For Prof. Joly's 

 statement see his Address to Section C of the British Association, 1908. Mr. 

 Clarence King's paper was published in the American Journal of Science, Jan. 1903. 



