VOLCANOS AND RADIOACTIVITY 267 



One of the problems at present unsolved is : Whence comes this 

 radioactive material, and what maintains its activity ? For the most 

 part, it gives us the characteristics of radium, and in smaller degree 

 those of thorium and uranium. The action of actinium has not yet 

 been sufficiently pronounced to be recognized. Polonium is believed 

 to be one of the transitional forms of radium. No other radioactive 

 substances are yet known. The most important one thus far identi- 

 fied is radium. But the life and activity of radium are, from a 

 geological standpoint, very brief. According to Professor Rutherford 

 — and he is sustained by nearly all other physicists — radium is half 

 consumed in a period of 1,300 years. In 13,000 years only the 

 thousandth part of what now exists will be left, and in 26,000 years 

 only the millionth part will remain. Quite independently of geological 

 reasons, the belief has been that radium is generated as the product 

 of decay of some other element, and that the amount of it in nature 

 is sensibly constant. It is generated as rapidly as it decays. The 

 parent element from which it may be derived is not yet decided, but 

 there are some who suspect it to be uranium, which has immensely 

 long life. It requires nearly 120,000,000 years to be half consumed 

 by its own decay. 



But we are not interested in pursuing and trying to test these un- 

 solved problems. It is enough for us that radioaction exists in suffi- 

 cient quantity and intensity to furnish heat enough to meet the wants 

 of the vulcanologist. 



Let us now look for a moment at the presumable details of the 

 process. At a depth of two or three miles in the earth let us assume 

 that radium is in process of being generated. It starts at once upon 

 that process of transfomation of which one stage is the production of 

 the so-called emanation, which is a gas of very high density and great 

 penetrating power and diffusability. We know that the upper strata 

 and soils everywhere contain it, and no reason appears why the same 

 should not be the case with the rock beneath. Wherever the emana- 

 tion penetrates, the breakup of its particles generates heat, and the 

 temperature rises in proportion to the amount of emanation which 

 undergoes transformation in a given time, and falls in proportion to the 

 rate at which it is conducted away. So long as the gain of heat exceeds 

 the loss, so long will the temperature rise until it becomes sufficient to 

 melt the rocks. 



