22 



PRESIDENT S ADDRESS — SECTION A. 



the earth's whole surface. The nature of the data is indicated by 

 the following estimates^ : — 



TEMPERATURE GRADIENT 



There is more uncertainty in the value of k than in that of d0/dr. 

 A more accurate estimate of the heat loss of the earth is desirable. 

 Convection currents make the conduction method ordinarily 

 inapplicable to the sea or lakes, but under special conditions, such 

 as fresh water between 0° and 4° C, might not the method be 

 applicable to a lake ? 



Heat from Uranium and Thorium in Rocks. — Lord Kelvin 

 supposed that this heat stream of 6 x 10^^ calories per sec. came 

 from the sensible heat of the earth's interior which is thereby cooled. 

 That the heat of disintegration of radium might play an important 

 part in cosmical physics was pointed out by Rutherford and Soddy-. 

 The accurate determination of radium and thorium in rocks has 

 shown there is an embarrassingly large supply of heat being con- 

 tinuously emitted by these substances. A number of determina- 

 tions of radium in rocks have been made by Strutt and Joly, but 

 there is need for a systematic survey. 



Radium in Igneous Rocks. — 



mean 64 

 126 



1.3 

 7.01 



Joly (Radioactivity and geology, 

 P.M. Oct., 1909) 



1. Toly, " Radio-activitv and Geology." 

 2.. Phil. Mag. May. 190:i. 



