196 F W. Very— A Cosmic Cycle. 



a mean of all known observations, it seems proper to choose 

 those which give the slowest rates of thermal increment, for 

 these are the ones which have been least interfered with by 

 local volcanic action, and which most nearly correspond to the 

 deeper and more stable gradients. The substitution of these 

 slowest rates increases the time scale. 



Clarence King* has given a different method, depending on 

 the fusion temperature of basalt as determined by Barus, and 

 assumptions as to the average composition of the earth's outer 

 layers, which are supposed to be basaltic. But the eruptive 

 rocks are just those which have been, as it were, sweated out 

 from the crust, leaving the more refractory materials behind. 

 Grant this, and the average melting point of the residual rocks 

 must be raised, increasing the time-estimate by this method. 

 Taking the initial temperature of solidification as 1741° C, 

 Clarence King finds for a thermal gradient of 1° F. in 50 feet, 

 20X10 6 years, and for 1° F. in 75. feet, 46X10 6 years, on the 

 hypothesis of a solid earth. Neither estimate takes any account 

 of the greater conductivity of the deeper layers. If this were 

 done, it might be necessary to extend the computed durations 

 several times. + 



Finally, if the gradual modification of living forms by natural 

 selection is a fact, the longest durations named are none too 

 long for the numerous successive faunas and floras made known 

 to us by paleontology. 



We need an earth-duration of several hundred million years 

 to meet the requirements of evolutionary theory and of ther- 

 motics. The sun, by its contraction, will give only 20,000,000. 

 Hence the dilemma. 



The hypothesis of the development of solar energy by atomic 

 dissolution greatly extends the duration of the sun, in all prob- 

 ability doing away with this dilemma. 



The companion hypothesis of an atomic genesis by luminous 

 impulses, in addition, fulfills the philosophic necessity for a 

 cosmic cycle which shall restore the ancient order, and answers 

 the question : What becomes of the light from these myriads 

 of stars? 



Washington, D. C. 



* This Journal (3), vol. xlv, p. 1, 1893. 



f See Professor John Perry, " On the Age of the Earth," Nature, vol. li, p. 582, 

 1895. 



