58 ILLINOIS ACADEMY OF SCIENCE. 



tion was thought to have given rise to intense heat. The primitive 

 hot and gaseous or quasi-gaseous earth-mass was held to have 

 passed later into a molten globe, and the subsequent encrusting 

 of this entrapped in the interior the heat supply of subsequent 

 ages. This older view was still in general possession of the field 

 when the apparition of radioactivity forced a new line of thought. 

 But there was also an alternative view built on the belief that the 

 earth grew up gradually by the slow accession of discrete orbital 

 matter in distinction from the direct condensation of a gaseous or 

 quasi-gaseous mass. In this view, the internal heat arose mainly 

 from the self-compression of the earth-mass as it grew. This 

 view had its origin in the grave cosmogonic difficulties that had 

 been discovered in the gaseous and quasi-gaseous theories of the 

 earth's origin. Of the two rival views thus already in the field, 

 the one postulated a plethora of heat at the outset and a gradual 

 loss in all later time, the other postulated at the outset a more 

 limited supply of heat which was increased as compression pro- 

 gressed. The adequacy of such compression to give a sufficiency 

 of heat was a subject of debate from the inception of the view.'^ 

 To the interest that naturally attaches to the discovery of a wholly 

 unexpected agency, already acute because of the agent's singular 

 qualities, there was thus added piquancy in view of its inevitable 

 bearings on the thermal problem of the earth's interior and on the 

 hypotheses of the earth's origin. 



An even more fundamental though less imminent interest was 

 awakened by the discovery that some of the atoms of the earth- 

 substance are undergoing spontaneous disintegration and that all 

 atoms may possibly be doing so and that even the permanency of 

 terrestrial substance may be brought into question. However, 

 matters of this ultra-radical nature cannot be discussed with 

 advantage as yet for little light has been shed on the broad ques- 

 tion whether all terrestrial substance is in process of disintegra- 

 tion and on the complementary question whether atoms are some- 

 where and somehow undergoing integration. 



If the general tenor of the studies thus far made is to be trusted, 

 nothing in the field of common experience seriously inhibits the 

 dissolution of the radioactive substances. It does not appear that 

 even the greatest heightening or lowering of temperature or pres- 

 sure that can be brought to bear either stays or hastens, in any 



2The status of the problem of the earth's heat as it stood near the opening of 

 the twentieth century is sketched more fully in Year Book No. 2, Carnegie Institu- 

 tion, 1903, pp. 262-265, and in Chamberlin and Sahsbury's Geology, Vol. 1 (1904), 

 pp. 533-547. 



