THE 



AMERICAN JOURNAL OF SCIENCE 



[THIRD SERIES.] 



I 



Art. I. — The Age of the Earth; by Clarence King. With 

 Plates I and II. 



Among- the various attempts to estimate geological time 

 none has offered a more attractive field for further develop- 

 ment than Lord Kelvin's mode of limiting the earth's age 

 from considerations of its probable rate of refrigeration, 

 published in 1862.* At that time the consequences of his 

 physical reasoning could not be fully applied to the condi- 

 tions within the earth, so as to test the probability of his 

 hypothetical case, for want of positive knowledge of certain 

 properties of rocks, particularly the volume changes of melted 

 rock in approaching and experiencing congelation, and the 

 qualitative and quantitative effects of pressure upon the fusion 

 and freezing points. Data then lacking are for the first time 

 available, and with them it is proposed to apply a new crite- 

 rion to the gradient of Lord Kelvin and to compare with 

 it other cases of more probable earth-temperature distribution, 

 which should have the effect of advancing his method of 

 determining the earth's age to a further order of importance. 



Accepting the hitherto unshaken results of Kelvin and G. 

 EL Darwin, as to the tidal effective rigidity of the earth, and 

 the further argument for rigidity advanced by Prof. S. ]New- 

 combf from the data of the lately ascertained periodic variation 

 of terrestrial latitude, as together warranting a firm belief in the 

 rigid earth, it follows that solidity may be used as a criterion 



* Treatise on Natural Philosophy, Thomson and Tait, Part 2, Appendix D. 

 f Monthly Notices of the Royal Astronomical Society, vol. lii, No. 5, 1892. 



Am. Jour. Sci. — Third Series, Vol. XLV, No. 265.— January, 1893. 

 1 



