22 president's address. 



accepted that the eartli may be continuously deriving its supplies 

 of radium from solar emanations.* It is known that the 

 tangential speed of projection of the matter constituting the solar 

 emanations is sufficiently great to carry it out of control of the 

 sun's gravity and into the sphere of influence of the earth. Prof. 

 Joly thinks that this might account for tlie apparent limitation 

 of radium to the crustal skin of the earth. That other bodies 

 yield analogous disintegration products, accompanied by the 

 evohition of energy, is well ascertained, but in no known case is 

 this activity at all comparable with that of the uranium-radium 

 product. Still, however, it is quite in keeping with modern views 

 that all matter is in a more or less rapid condition of disintegra- 

 tion, and we cannot say how much of the heat of the earth's 

 interior may be due to the aggregate effect of disintegration and 

 transformation in the mass of matter of which it is composed. I 

 mentioned Sir William Crookes' views on this phase of the subject 

 in my address last year.f Possibly the earth's supply of radium- 

 producing elements ma}' be fairly evenly distributed throughout 

 its mass, and disintegration, while not altogether prevented, ma}' 

 be greatly curtailed by environment and pressure. Were this so 

 we might expect a considerably augmented radium production 

 when materials from beneath reach the surface through the agency 

 of volcanic action. This would account for the surface material 

 displaying so much greater radium activity than can possibly be 

 the case throughout the interior of the earth. At the same time 

 such a conception of the place of radium in the scheme of world 

 physics permits of the possible, and, for my part I think, highly 

 probable, retention by the earth of a portion of its original 

 gravitational heat. We should then have a cooling globe masked 

 by a heat-generating crust, the effect of which would be to 

 indefinitely delay the secular cooling of the heated centre. 



Assuming the heat of the earth's central mass to be due to the 

 original store of gravitational heat. Lord Kelvin has shown that 



* Nature, Ixxv., 1907, p.294. 

 t Pi-oc. Linn. Soc. New South Wales, 1905, p. 61 7. 



