230 THE NEW KNOWLEDGE. 



refused to be content with less than a thousand million. 

 The claims of each party to the controversy seemed to be 

 irrefragable and yet irreconcilable. As an example of the 

 physical method of calculation we may cite the method of 

 Lord Kelvin who deduced the age of the earth by a con- 

 *sideration of the interior l^at of the earth and the rise of k 

 temperature as one descends beneath the surface. 



This rise in temperature amounts to about one ^degree, ' 

 Centigrade, for every one hundred feet of descent, and tak- 

 ing the average heat conductivity of the earth as .004 

 (C. G. S. Units) this leads to the conclusion that ten million 

 years ago the surface of the earth was still molten, a con- 

 clusion absolutely unacceptable to the natural scientists. 

 This conclusion of the physicists rests on a certain assump- 

 tion which, however, at the time, seemed no assumption at 

 all. In a word they assumed that the earth was a self-cool- 

 ing body ; they did not imagine that it was a self-heating one 

 as well. We shall see that as a matter of fact the earth is 

 self-heating. 



One gram of radium yields about 100 calories of heat per 

 hour, or 864,000 gram-calories per year. Consequently, the 

 presence of 2.6 X 10 - 13 of radium per unit volume or 

 4.6 X 10 - 14 per unit mass would compensate for the heat 

 which the earth loses by conduction. Or, taking the case of 

 uranium, which probably does not evolve more that a mil- 

 lionth of the heat of radium, it may be shown that the pres- 

 ence of a very small fraction of this substance scattered 

 throughout the earth would be sufficient not only to keep 

 the earth's temperature constant but actually to raise it 

 from a cold condition to a hot xme. But do we actually find 

 in the ordinary earth a radio-activity adequate to furnish 

 heat sufficient to balance the earth's loss by conduction? 

 We certainly do. We have shown, pages 133 et seq., that all 



