URANIUM AND GEOLOGY." 



[With 1 plate.] 



By Prof. John Joly, M. A., D. Sc, F, R. S. 



INTRODUCTION. 



In our day but little time elapses between the discovery and its ap- 

 plication. Our starting point is as recent as the year 1903, when 

 Paul Curie and Laborde showed experimentally that radium steadily 

 maintains its temperature above its surroundings. As in the case 

 of many other momentous discoveries, prediction and even calcu- 

 lation had preceded it. Rutherford and McClung, two years before 

 the date of the experiment, had calculated the heat equivalent of 

 the ionization effected by uranium, radium, and thorium. Even at 

 this date (1903) there was much to go upon, and ideas as to the 

 cosmic influence of radio-activity were not slow in spreading.^ 



I am sure that but few among those whom I am addressing have 

 seen a thermometer rising under the injBiuence of a few centigrams of 

 a radium salt; but for those who pay due respect to the principles of 

 thermodynamics, the mere fact that at any moment the gold leaves 

 of the electroscope may be set in motion by a trace of radium, or, 

 better still, the perpetual motion of Strutt's " radium clock," is all 

 that is required as demonstration of the ceaseless outflow of energy 

 attending the events proceeding within the atomic systems. 



Although the term " ceaseless " is justified in comparison with our 

 own span of existence, the radium clock will in point of fact run down 

 and the heat outflow gradually diminish. Next year there will be less 

 energy forthcoming to drive the clock, and less heat given off by the 

 radium by about the one three-thousandth part of what now are 

 evolved. As geologists, accustomed to deal with millions of years, we 

 must conclude that these actions, so far from being ceaseless, are 



** Address to the geological section of the British Association for the Ad- 

 vancement of Science, at Dublin, 190S. Reprinted by permission, with correc- 

 tions by the author. 



^ See letters appearing in Nature of July 9 and September 24, 1903, from the 

 late Mr. W. E. Wilson and Sir George Darwin referring to radium as a solar 

 constituent, and one from the writer (October 1, 1903) on its influence as a ter- 

 restrial constituent. 



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