I 



T. Mellarcl Reade — Radium and Earth-shrinkage. 79 



VII. — Eadiuji and the Radial Shrinkage of the Eakth. 

 By T. Mellard Eeade, F.G.S., F.E.I.B.A., A.M.I.C.E. 



N his Presidential Address to the British Association, South 

 African Meeting, 1905, Professor G. H. Darwin points out that 

 the presence of radio-active materials in small proportion in the 

 sun would serve to explain the present radiation, and "that con- 

 centration of matter is not the only source from which the sun may 

 draw its heat." Professor Darwin goes on to explain how this 

 enables us to extend the possibilities of geological time beyond that 

 to which some physicists would limit us. 



My object in writing this is to point out that if the sun's heat is 

 kept up by the presence of radio-active materials the same must 

 follow with regard to the earth. The rate of cooling of the earth 

 must consequently be slower in proportion to the quantity of heat 

 generated by the radio-active matter present in its substance. 



It further follows from these premises that if the generation of 

 heat by these radio-active matters in the earth equals the dissipation 

 of it at the earth's surface the globe will be kept at the same average 

 temperature. If this be the condition of the earth at the present 

 time there can be no radial contraction taking place unless due to 

 some other cause than loss of heat, and the same may be predicated 

 of any previous period. 



This is no doubt stating an extreme case, but if, on the other 

 hand, we assume that only a portion of the heat lost by the earth 

 by conduction and radiation is replaced by that generated by radio- 

 active bodies, by so much will the radial shrinkage be reduced and 

 the mountain - making activities on the contraction hypothesis 

 rendered less efficient. 



It has been shown by Osmond Fisher and myself that the gradual 

 dissipation of the initial heat of the earth, considered simply as 

 a cooling body, that has taken place in the past is quite insufficient 

 to provide the radial contraction demanded by the contraction 

 hypothesis.^ If any of this lost heat is renewed this inefficiency is 

 proportionately intensified. 



Our ideas of the constitution of matter are undergoing serious 

 changes, and it becomes increasingly important that geologists should 

 keep themselves abreast of the times. The bugbear of a narrow 

 physical limit to geological time being got rid of, we are fi-ee to 

 move in our own field of science. The methods of geology have this 

 advantage over those of pure physics, we can more readily appeal to 

 nature for confirmation or disproof. 



May I be permitted to point out that while the discovery of 

 radium has shaken the foundations of what may be designated the 

 mathematical theory of the earth, it strongly supports those who 

 like myself have long contended that the forces which create 

 mountain ranges, raise continents, and give external form to the 



1 Fisher : ' ' Physics of the Earth' s Crust. ' ' Eeade : ' ' Origin of Mountain Eauges ' ' ; 

 " Evolution of Earth Structure." 



