352 THE AGE OF THE EARTH. 



selective absorption of either the sun's atmosphere or the eartli's, or 

 both, have varied reciprocally or concurrently with radiation, solar 

 einissiou can not have had a wide range of either secular or i»aroxys- 

 mal change. 



Xevertheless, the age assigned to the sun by Helniholtz and Kelvin 

 (15x10^ or 20x10*^ years) communicated a shock from which geologists 

 have never recovered. The thermo-dynamic reasoning on which the 

 brevity of the sun's life is reached stands undisturbed, yet so powerful 

 is the influence of the old uniformation method of estimating the age of 

 the total stratified crust, that to many geologists it has seemed easier 

 to reject the physical conclusions than to seek a source of error in our 

 own very vulnerable methods. 



If, as 1 hold, Kelvin's suggestions as to ellipticity and tidal retarda- 

 tion do not apply to an earth readily deformable by slow stress, as this 

 one evidently is, there remain but three earth-ages to be weighed — 

 Kelvin's value from terrestrial refrigeration, which this i)ai)er seeks to 

 advance to a new precision ; Helmholtz and Kelvin's age of the sun, 

 which nuist sharply limit the date of the re-distributed earth crust ; and 

 the old stratigraphical method. From this point of view the conclu- 

 sions of the earlier part of this paper become of interest. The earth's 

 age, about twenty four millions of years, accords with the fifteen or 

 twenty millions found for tlie sun. 



In so far as future investigation shall prove a secular augumentation 

 of the sun's emission from early to present time in conformity with 

 Lane's law, his age may be lengthened, and further study of terrestrial 

 conductivity will probably extend that of the earth. 



Yet the concordance of results between the ages of sun and earth, 

 certainly strengthens the physical case and throws the burden of proof 

 upon those who hold to the vaguely vast age derived from sedimentary 

 geology. 



