president's address. 21 



Lord Kelvin does not acquiesce in the above theory of earth- 

 heat; he considers it highly probable that the conditions of 

 pressure and environment at a short distance from the earth's 

 surface are sufficient to effectually prevent the disintegration of 

 radium and hence the evolution of heat.^ 



The heat evolution from 1 gram of radium amounts to 06785 

 British thermal units per hour, or 5944 in a year, which is 

 equivalent to the evaporation of 175 lbs. of water per annum by 

 1 oz. of radium. The mechanical equivalent of the latter maybe 

 expressed as being equal to the raising of 577 tons 100 feet above 

 the earth's surface. It is startling to think that this enormous 

 thermal energy is evolved in the time stated with the loss of but 

 a minute fraction of the weight of the radium involved. Pro- 

 fessor Rutherford estimates the energy equivalent of radium as 

 at least a million times that of any other known molecular 

 combination.! 



As the most moderate estimate of the quantity of radium in 

 the rocks constituting the earth's crust is amply sufficient to 

 account for the observed heat gradient near the surface, if what 

 I might call the extreme radium theor}?- be accepted as accounting 

 for the present thermal condition of the earth, it becomes neces- 

 sary to abandon the idea of there being any serious quantity of 

 the original gravitational heat remaining. It is the essence of the 

 extreme radium hypothesis that a condition of thermal equilibrium 

 has been attained, that the earth is neither getting hotter nor 

 cooler and will remain in its present condition so long as the 

 production of radium continues at an adequate rate. That there 

 must be a time limit is obvious, for the supply of uranium or 

 other radium-yielding material cannot be inexhaustible, but con- 

 sidering the enormous energy equivalent of radium, we see that 

 exceedingly small proportions are adequate to yield the required 

 heat for a very long period. The possible extension of time is 

 enormously increased if a recent suggestion of Prof. J. Joly be 



* Chem. News, xciv., 21 Sept. 1906, p. 145. 

 t Rutherford, "Eadio-Activity," 2nd ed., p. 482. 



