RADIUM 63 



It was clearly shown by these investigators that the 

 heat resulting from the oxidation of marcasite (iron sul- 

 phide) in coal seams is three times as much as is required 

 to account for the total rise in temperature, which the air 

 of the ventilating current undergoes in passing through 

 the mines. 



But recently a new cause of disturbance has been 

 discovered, and this looms up before us, vague and 

 gigantic, threatening to destroy all faith in hitherto 

 ascertained results, and to shatter the fabric of reasoning 

 raised upon them. This apparition is radium, with its 

 companion radio-active bodies. 



The special property of radium which concerns us 

 here is the apparently spontaneous evolution of heat, 

 which accompanies its existence, or perhaps its destruc- 

 tion, as it disintegrates into simpler constituents. A 

 gram of radium emits something like 90 or 100 gram 

 degrees of heat per hour, or as much as escapes on the 

 average from two square yards of the earth's surface in 

 the same time. Hence, since radium is a constituent of 

 the earth's crust, it furnishes us with a new and un- 

 expected source of terrestrial heat ; * and it has been 

 asserted that if radium is distributed uniformly through- 

 out the earth's volume, to the extent of 1-5, 000, 000th of 

 a gram per cubic metre, this would be sufficient to 

 compensate for the whole of the heat lost by radiation 

 into outer space, and thus to maintain the temperature 

 gradient unchanged for a very long period. f Whether 

 radium is present to this extent throughout the globe, 

 and whether under the conditions which exist in the 

 interior it would behave as it does at the surface, are 



* C. H. Darwin, " Radio-activity and the Age of the Sun," Nature, 

 vol. Ixviii., p. 496, 1908 ; J. Joly, " Radium and the Geological Age of 

 the Earth," ibid., p. 526. 



| G. Liebenow, Nature, vol. Ixxi., p. 113, 1904, 



