SYMPOSIUM ON R-\DIOACTIVITY. 65 



greatly subdued or possibly inhibited altogether. This plausible 

 explanation was diligently tested ; but the general tenor of experi- 

 ments on the effects of pressure, notably those of Eve and 

 Adams,® in which the pressures were carried to intensities sufti- 

 cient to cover earth-pressures to the depths supposed to limit 

 radioactivity and beyond, showed no appreciable restraint on the 

 disintegrating process. It seems necessary-, therefore, in the 

 present state of evidence, to accept the inference that the radio- 

 active substances are really concentrated toward the surface, and 

 that the radioactive content in the depths of the earth is of a 

 much lower order. 



It does not fall to me to adjust the new requirements to the 

 older view of the earth's internal temperatures based on a molten 

 earth, for other considerations led me to the abandonment of this 

 view before the advent of the new issue. I must leave to those 

 who hold to the molten hypothesis to battle with its new perils. 

 With such a plethora of heat at the start as a molten earth implies 

 and with a new agency whose current production of heat would 

 seem to be excessively great if its prevalence were not construc- 

 tively minimized, it is not with regret that I feel absolved from 

 the task of finding a reconciliation between this venerable view 

 and the requirements of juvenile discoveries. 



The discussion of Professor Joly.^'^ though not explicitly based 

 on the theor}- of a molten earth, is sympathetic with the general 

 tenets associated with such an earth, and his treatment may be 

 taken as offering the best approach to a reconcihation that seems 

 now possible. 



It is interesting to note, however, that when Professor Toly 

 reached the critical question of a possible mode by which the 

 surface concentration of radioacti\'it}' could have come about 

 (Radioactivity and Geolog};. p. 184) he turned to the accretion 

 or planetesimal hypothesis. While he indicated the central line 

 of action on which the concentration might have been accom- 

 plished he left without elucidation the line of reconciliation be- 

 tween the heat gradient postulated by the planetesimal view and 

 the gradient he deduces from radioacti\'it\-. 



It is the chief purpose of this paper to set forth what seems 

 to me to be the true harmony between the new light shed by radio- 

 activity and the tenets of the planetesimal view as shaped by me 

 before the discoverv of radioactivitv and to show the co-ordina- 



•Nature, July, 1907, p. 269. 

 ^•Radioactivity and Geology, pp. 154-183. 



