CONVERGENCE OF EVIDENCE \)^6 



lias been nearly constant. This constancy suggests that the sun was 

 already past the formative period in the earliest times for which there is 

 a geological record and has not yet entered into the declining stages of 

 its history. In view of these facts, it is seen that even for an age of 

 50,000,000 years the hypothesis of solar energy due to gravitational infall 

 seems hopelessly inadequate. What, then, shall be said of an age as great 

 as 1,500,000,000 years ? It is of the order of one hundred times too great. 

 The issue is sharply drawn and indicates that either geological time has 

 been overestimated a hundred fold or the hypothesis of self-contraction 

 as the source of solar energy does not account for more than perhaps 

 I per cent of the expenditure. 



This problem has been discussed also by Holmes.^^^ Eutherford and 

 Soddy in 1903 pointed out the possible importance of radio-thermal action 

 in the sun, but Wilson in the same year showed that, if the sun were 

 wholly composed of uranium and thorium in equilibrium with their dis- 

 integration products, the radioactive disintegration, although ample in 

 duration, would give rise to only a fraction of the daily expenditure of 

 solar energ}\ Holmes finds, on account of the slowness of these trans- 

 formations, that by no possibility could more than one-tbird of the sun's 

 lieat be accounted for by the ladioactivity of uranium and thorium. 

 Either, then, there are furtlier atomic disintegrations which snpi)ly more 

 heat or, as Arrhenins has suggested in more general form, tliere are higher' 

 stores of energy which may be liberated by changes in physical states at 

 high temperatures and great pressures, latent heat being given out as 

 thermal energy by their transformations. ^^^ Of course, such suppositions 

 only emphasize our ignorance of the cosmic process, for before this energy 

 can be liberated it must in some manner have been stored. For example, 

 the enormous energy liberated by the stepping down of uranium^ with 

 molecular w^eight 232.2, into lead of molecular weight 206.2 must previ- 

 ously have been absorbed in the building up of uranium. The lead in its 

 origin has presumably still stored within its atom much more energy than 

 is liberated by its generation from uranium. 



Such intra-atomic energies may be inferred for the elements which are 

 not radioactive from analogy with those that are and also from the higher 

 incompressibilities of the elements of small atomic volume. An external 

 load only slightly condenses the sphere of influence which may be re- 

 garded as the volume of the atom, and the work of condensation is ab- 



150 Arthur Holmes: The age of the earth, 1913. Chapter VIII, the thermal energy of 

 the sun. 



isi Svante Arrhenius : The life of the universe, vol. ii. chap. viii. The energy concep- 

 tion in cosmogony, 1909. 



LXVII — Bull. Geol. Soc. Am., Vol. 28, 1916 



