PRESIDENTIAL ADDRESS. 679 



materials leave still a large balance of certainty — so far as tlie word is allo-waljle 

 when applied to the ever-widening views of tcieiice — upon which to base our 

 deductions. The emanation of radium is most chavacteri.'itie in beliaviour; know- 

 ledge of its peculiarities enables us to distinguish ita presence in the electro- 

 scope not only from the emanation of other radio-active elements, but from 

 any accidental* leakage or inductive disturbance of the instrument. The method 

 of measurement is purely comparative. The cardinal facts upon the strength of 

 which we associate radium with geological dynamics, its development of heat and 

 its association with uranium, are founded in the fir.st case directly on observation, 

 and, in the second, on evidence so strong as to be equally convincing. Recent 

 work on the question of the influence of conditions of e.vtreme pressures and 

 temperatures on the radio-active properties of radium appear to show that, as 

 would be anticipated, the effect is small, if indeed existent. As observed by 

 Makower and Rutherford, the small diminution ■ jtieed under very extreme con- 

 ditions in the y radiatiin possibly admits of explanation on indirect ertects. These 

 observations appear to leave us a free hand as regards radio-thermal effects unless 

 when we pursue speculations into the remoter depths of the earth, and even there 

 while they remain as a reservation, they by no means forbid us to go on. 



The precise quantity of heat to which radium gives rise, or, rather, which its 

 presence entails, cannot be said to be known to within a small percentage, for the 

 thermal equivalent of the radio-active energy of uranium, actinium, and ionium, 

 and of those members of the radium family which are slow in changing, has not 

 been measured directly. Professor Rutherford has supplied me, however, with 

 the calculated amount of the aggregate heat energy liberated per second by all 

 these bodies. In the applications to which I will presently have to refer I take 

 his estimate of 5-6 x lO"^ calories per second as the constant of heat-production 

 attending the presence of one gram of elemental radium. 



To these words of introduction I have to add the remark, perhaps obvious, 

 that the full and ultimate analysis of the many geological questions arising out of 

 the presence of radium in the earth's surface materials will require to be founded 

 upon a broader basis than is afforded by even a few hundred experiments. The 

 whole sequence of sediments has to be systematically examined; the various classes 

 of igneous materials, more especially the successive ejecta of volcanoes, fully 

 investigated. The conditions of entry of uranium into the oceanic deposits has 

 to be studied, and observations on .sea- water and deep-sea sediments multiplied. 

 All this work is for the future ; as yet but little has been accomplished. 



The Radium, in the Rocks and in the Ocean. 



The fact first established by Strutt that the radium distributed through the 

 rock materials of the earth's surface greatly exceeds any permissible estimate of 

 its internal radio-activity has not as yet received any explanation. It might 

 indeed be truly said that the concentration of the heaviest element known to us, 

 (uranium) at the surface of the earth is just what we would not have expected. 

 Yet a simple enough explanation may be at band in the heat-producing capacity 

 of that substance. If it was originally scattered through the earth-stuff, not 

 in a uniform distribution but to some extent concentrated fortuitously in a 

 manner depending on the origin of terrestrial ingredients, then these radio- 

 active nuclei heating and expanding beyond the capacity of surrounding materials 

 would rise to the surface of a world in which convective actions were still pos- 

 sible and, very conceivably, even after such conditions had ceased to be general : 

 and in this way the surface materials would become richer than the interior. 

 For instance, the extruded mass of the Deccan basalt would fill a sphere 36 miles 

 in radius. Imagine such a sphere located originally somewhere deep beneath the 

 surface of the earth surrounded by materials of like density. The ultimate excess 

 of temperature, due to its uranium, attained at the central parts would amount to 

 about 1000° C, or such lesser temperature as convective effects within the mass 

 would permit. This might take some thirty million years to come about, but before 

 80 great an e:!?:ces3 of temperature was re£iche4 the force of buoyancy developed in 



