Clarence King — Age of the Earth. 



15 



How this correction, of at present unknown value, affects 

 the coordinates of a given gradient qualitatively, is shown 

 by the following figure in which are given the diabase melting 

 point and pressure line, D D, gradient b of 3900° C. excess and 

 100x10 s year's cooling, with the viscosity transitional line Y V 

 intersecting it, also a dotted line c, indicating the position of 

 the b gradient corrected for diminished conductivity (viscosity). 



Lagging to the right of the uncorrected gradient obviously 

 the dotted line would require longer refrigeration to reach the 

 state of solidity, and it is equally important to note that its 

 position requires its emergence at the surface with a higher 

 rate than the uncorrected line and thus extends the time of 

 cooling down to the mean rate which marks for all gradients 

 the present limit of the process. 



c. Liquid-solid conductivity. Closely involved in the above 

 heat-pressure- viscosity correction is the change of conductivity 

 on passing isothermally from solid to liquid. Here again the 

 results of Dr. Barus* throw important light. 



The relatively higher thermometric conductivity of the solid 

 over the liquid of equal temperature indicates an additional 

 plus correction for time values. 



Both the minus correction due to convection, and the plus 

 corrections based upon conductivity diminished below the 

 Everett figures, sink in importance as we pass from earths of 

 higher to those of lower initial excess, so that until some ap- 

 proximate quantitative values can be given them we have no 

 warrant for extending the earth's age beyond 2£ millions 

 of years. 



* The change of heat conductivity on passing isothermally from solid to liquid. 

 C. Barus, this Journal, July, 1892. 



