128 G. F. BECKER RELATIONS OF RADIOACTIVITY TO COSMOGONY 



evidence of the absence of the radioactive elements from the sun is not 

 merely negative. The probabilities are that these elements are built np, 

 say from lead and helium, only in cooling stars or in planetary masses. 



If uranium is assumed to be present in the stars and nebulae, the mys- 

 tery of the universe is portentously increased. Eegarding uranium as 

 compounded of lead and helium, it is substantially inevitable to suppose 

 that it was formed under conditions in which it was stable. The only 

 alternative is to imagine it an evanescent product of the spontaneous 

 decomposition of still heavier atoms and then it must be assumed that 

 these were stable. Now Pb.Heg is an endothermic compound and almost 

 incomparably more endothermic than any other except its fellow-members 

 of the radioactive group. Its genesis, therefore, was accompanied by the 

 absorption of a vast amount of energy locally concentrated and thus of 

 great intensity. The cold and tenuous, gaseous nebulae, whose density is 

 less than that of the best laboratory vacuum, afford no mechanism for 

 such a process. Uranium in the nebulge would point to a precedent con- 

 densation, to a regeneration of the nebulous state from an aged solar 

 system, such as was imagined by Immanuel Kant.-** But such a process 

 stands in conflict with the second law of dynamics and implies that the 

 systenl is a perpetuum mobile. Only the discovery of fundamental laws 

 of physics of which there is as yet no inkling would suffice to explain the 

 presence of uranium in nebulEe. 



It is the effort of science to reduce the facts of nature to their simplest 

 exjjression. "From the earliest times there has been a tendency to regard 

 varieties of matter as derivative," -^ and to seek their origin in an undif- 

 ferentiated protylie substance or Urstoff', as Kant called it. It is hardly 

 possible to think of a truly primitive nebula otherwise than as composed 

 of protyle. From the modern point of view, the atoms of this substance 

 would be the simplest systems of corpuscles capable of stable equilibrium, 

 and it is not impossible that coronium satisfies this definition. 



There is thus, so far as I can see, neither direct evidence that the sim 

 is a radioactive body, nor is the hypothesis that it is radioactive inherently 

 probable. There is also very little evidence that the meteors are radio- 

 active. Mr L. J. Strutt -** found substantially no radioactivity in sider- 

 ites. Some of the stony meteorites show activity, but they are not known 

 to contain uranium and thorium minerals and may well have acquired 

 their activity from terrestrial emanations. 



On earth the crystallized uranium and thorium minerals are confined, 

 so far as is known, to the pegmatitic modifications of the granitic and 



2" Kant" s Werke, Ilartenstein, Leipzig, vol. 1, 18fi8, p. .302. 



^ A. M. Clerke : Modern cosmogonies, 1005, p. 148. 



2s Proceedings of the Royal Society, series A, vol. 77, 1906, p. 472. 



