700 



SCIENCE 



[N. S. Vol. XXVIII. No. 725 



the applications to which I will presently 

 have to refer I take his estimate of 

 5.6 X 10"^ calories per second as the con- 

 stant of heat-production attending the pres- 

 ence 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 geo- 

 logical 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 hun- 

 dred experiments. The whole sequence of 

 sediments has to be systematically ex- 

 amined; the various classes of igneous ma- 

 terials, more especially the successive ejecta 

 of volcanoes, fully investigated. The con- 

 ditions of entry of uranium into the 

 oceanic deposits has to be studied, and ob- 

 servations on sea-water and deep-sea sedi- 

 ments multiplied. All this work is for the 

 future; as yet but little has been accom- 

 plished. 



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 in- 

 ternal 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 sur- 

 face of the earth is just what we would 

 not have expected. Yet a simple enough 

 explanation may be at hand in the heat- 

 producing capacity of that substance. If 

 it was originally scattered through the 

 earth-stuff, not in a imiform distribution 

 but to some extent concentrated fortui- 

 tously in a manner depending on the origin 

 of terrestrial ingredients, then these radio- 

 active nuclei heating and expanding be- 

 yond the capacity of surrounding materials 

 would rise to the surface of a world in 



which conveetive actions were still possible 

 and, very conceivably, even after such con- 

 ditions had ceased to be general; and in 

 this way the surface materials would be- 

 come richer than the interior. For in- 

 stance, 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 tempera- 

 ture, due to its uranium, attained at the 

 central parts would amount to about 1,000° 

 C, or such lesser temperature as conveetive 

 effects within the mass would permit. This 

 might take some thirty million years to 

 come about, but before so great an excess 

 of temperature was reached the force of 

 buoyancy developed in virtue of its thermal 

 expansion must inevitably bring the entire 

 mass to the surface. This reasoning would, 

 at any rate, apply to material situated at 

 a considerable distance inwards, and may 

 possibly be connected with vuleanieity and 

 other crustal disturbances observed at the 

 surface. The other view, that the addition 

 of uranium to the earth was mainly an 

 event subsequent to its formation in bulk, 

 so that radio-active substances were added 

 from without and, possibly, from a solar 

 or cosmic source, has not the same a priori 

 probability in its favor.* 



I have in this part of my address briefly 

 to place before you an account of my ex- 

 periments on the amounts of radium dis- 

 tributed in surface materials. Here, in- 

 deed, direct knowledge is attainable; but 

 this knowledge takes us but a very few 

 miles inwards towards the center of the 

 earth. 



The Ignecus Rocks.— T!he basalt of the 

 Deccan, to which I have referred, known 

 to cover some 200,000 square miles to a 

 depth of from 4,000 to 6,000 feet or more, 

 appears to be radio-active throughout. A 



'Nature, LXXV., p. 294. 



