1907.] 



AND CONTRACTION OF THE EARTH. 



223 



Strutt's curve of temperature calculated on the hypothesis that 

 radium in the earth's crust is the principal cause of the observed 

 internal heat of the globe. (Proc. Roy. Soc, Vol. yy, 1906.) 



III. On the Age of the Consolidation of the Globe and on 



THE Second Approximation to the Law of Temperature 



Near the Surface. 



§ 13. Consideration of the Twelve Fourier Solutions. 



The methods here employed are those of Fourier, with the con- 

 stants determined by Lord Kelvin. In view of the great uncertainty 

 heretofore prevailing respecting the age of the earth's consolidation, 

 we have thought it advisable to consider in all twelve cases, namely, 

 three distinct times, of 10,100, and 1000 million years each, and four 

 initial temperatures of 2000°, 4000°, 8000° and 12,000° Fahr. re- 

 spectively. These twelve solutions are illustrated by the diagrams 

 in the accompanying plate. If the earth had been of uniform tem- 

 perature throughout, no doubt its actual history would be essentially 

 included in one of the accompanying diagrams. 



But we have already seen reasons for holding that the central 

 temperature was very high, and the surface temperature quite low ; 

 and moreover there is no doubt that the secular cooling is confined 

 almost entirely to the crust. In considering the age of our earth 



PROC. AMER, PHIL. SOC. , XLVI. l86 P, PRINTED SEPTEMBER 4, I907. 



