Letter | Published:

Radioactivity and the Heat of the Earth


IN a previous letter to NATURE (vol. 119, p. 277, 1926) I have discussed Dr. J. W. Evan's suggestion that the existence of pleochroic haloes in mica indicates that much of the energy of the rays from the radio-elements in rocks is used up in producing physical, chemical, or atomic rather than thermal changes in the surrounding minerals. I concluded that the close agreement between the calculated and measured heat productions of the radio-elements affords strong evidence for the view that “practically the whole of the energy associated with the radiations emitted by these elements is available for raising the temperature of the rocks in which they occur.” In a later communication (NATURE, vol. 119, p. 424, 1926), Dr. Evans infers that if measurements of the heat production of radium were carried out in a mica container instead of in a glass tube, the results of experiment and theory might not show such good agreement, in spite of the fact that the fluorescence effects and colorations produced by the radiations and the thermo-luminescence resulting from subsequent heating of the coloured materials are quite analogous for the two substances. From the viewpoint of geothermal problems, the importance of an unequivocal decision on the question at issue is perhaps sufficient justification for my returning to the subject, for several independent lines of thought support the conclusion arrived at in my previous letter.

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