336 



NATURE 



\2 



hotter ihnn now the only contradiction to a ** heating'Up " 

 earth. 



Assumint^, ii<i before, the nniiquity of the earth to be 

 at lrn«t 301) inillinn y»>ar« (0. thf-n in ihnt pcrio*! n wupply of 

 heat of 3X 10- " cal. per gm. per »ec. (/i) would have raised 

 the interior of the earth to a temperature givrn by 



tf«3Xio-'*X3X io'X3>3 X ioVo-02 = 14,000'' C, 



when- S is the specific heat of the interna! material. 

 Though loss by conduction to the surface and latent heat 

 efTects are here nef^lected, the calculation is sufficient to 

 show that p uniform distribution of the radio-active 

 elements would give rise to internal temperatures too high 

 to be reconciled with the observed temperature gradients." 

 Wo may safelv conclude that there is very much less 

 uranium, radium, and thorium in the inner portion of the 

 earth than there is in the crust, and a maximum limit may 

 be assigned to the content of radio-active elements. It 

 would appear a minimum limit may also be set. 



Accorditif,' to Lord Kflvin, as we have seen above, a 

 period of cooling of more than forty million years could 

 not have elapsed betwoon tho solidification of the torrfstrial 

 crust and the establishment of the present temperature 

 gradient. If, however, the antiquity of the earth is more 

 than 300 million years, then the temperature gradient has 

 been maintained by some other source of heat, and the 

 radio-activity of the rocks is amply suflRcient for the pur- 

 pose if it extends to quite moderate depths. The present 

 temperature gradient would be maintained for an indefinite 

 time if the stream of heat from the interior came from the 

 radio-activity of the rocks. 



There would need to be 6x io'*/o-o6= 10'* gm. of terres- 

 trial radium to supply the heat lost by conduction, for a 

 layer of the earth's crust 14 km. deep, if of density 3, has 

 a mass of 2-1x10**, and it would give out 2ixio"x3X 

 io-" = 6xio'* cal. /sec, assuming the content in this 

 surface layer of radium and thorium, and therefore the 

 heat emission was that of tho surface rocks. There is verv 

 probablv at least this amount of the radio-active elements ; 

 otherwise it is not apparent why the temperature gradient 

 of the crust has its present value, though the antiquity of 

 the earth probably exceeds 300 million years. If the age 

 greatly exceeds that period, then the present temperature 

 gradient can depend but little on the secular cooling of the 

 earth from a molten state. 



Prof. Strutt '* has determined the minimum age of 

 thorianite by evaluating the ratio 



The quantir v of heli um in the mineral at nre«e nt 

 The rate at which the helium i» prodii-wl 



The refinement of the experiment will be appreciated when 

 it is recalled that the rate of production .of the helium is 

 only 4X I0-* c.c. per gm. of thorianite per year. He found, 

 as already mentioned. 280 million years for the age of one 

 specimen and 250 millions for another. 



To deduce a minimum age for a mineral in this manner 

 it must be assumed that — 



(i) There was no original store of heliutn in the mineral 

 when it was formed. 



(2) The mineral has not gained helium at anv time except 

 as it does now. 



(3) That the present rate of accumulation of helium is 

 th»- sam» as in the remote past, when possiblv high pressures 

 and temperatures obtained. 



The observational basis for these assumptions are : — 

 For (1) and (2). If the helium was originally present in 

 tho mineral when it was formed, or added later, then we 

 would expect to find helium in other minerals in which 

 helium is not now accumulating, but no such minerals 

 are known. Helium is only found in appreciable quanti- 

 ties when associated with thorium and uranium. The 

 mechanism " of how it is continuously and unchanginglv 

 produced from these elements is known in great detail. 



For (3)- That radio-active changes are independent of 

 temperature and pressure has been repeatediv tested and 

 confirmed. 



" This will be seen at once to follow from a calculation given by Strutt, 

 Proc Roy. Soc., p. 482, 1906. 

 IS Proc. Roy. Soc., Ixxxiv., ■;79, 1910. 

 " See for example Rutherford, Nobel lecture, iy>8. 



NO. 2201, VOL. 88] 



UNIVERSnV AND EDUCATIONAL 



INTELLIGENCE. 



The Marquise Arconati Vicconti has made • donation 



?ioo,ooo francs to the University of Paris, to be empk>> 

 or the benefit of the faculties of science and arts. 



In connection with the Institute of Chemistry, Mr. C. i 

 Cross will deliver the first of two lectures on " Cellulo*' 

 at University College, London, on Friday, Janu.i: 

 Sir William Ramsay, K.C.B., F.R.S., will preside- 



The post-graduate scholarship, of the value of 200/. per 

 annum, in naval architecture has been awarded by the 

 Royal Commissioners for the Exhibition of 1851 to M" 

 .Arthur Cannon, of Glasgow University, and formerly 

 the Royal Naval College, Greenwich. 



We learn from the issue of Science for December : 

 1911, that nearly a hundred students from the college -. 

 engineering of the University of W'isconsin were then on 

 their yearly tour of inspection of great engineering plants 

 of the eastern States. Engineering plants in Chicat 

 .Milwaukee, Niagara Falls, Pittsburg, Schenectady. N.^ 

 and New York City were visited. These tours are re- 

 quired of students of engineering during their junior and 

 senior years, and are arranged to cover industries that 

 illustrate the work of the course pursued by the student. 

 Four professors accompanied the students on their tour of 

 inspection. 



The annual meeting of the Geographical Association ■• 

 be held on January 13 at University College, Gower ^ 

 London, W.C. In the morning, at 11 a.m., a di- 

 on the organisation of home-work in school geograpnv uui 

 be opened by Prof. L. W. Lyde, and a paper on the popula> 

 tion of the world will be read by Prof. A. J. Her^' rt^nn 

 In the afternoon, at 3 p.m., Dr. G. R. Parkin wil! 

 his presidential address, and afterwards Prof. H<: 

 will exhibit lantern views of typical land-forms 

 by a committee of the International Geographical C 

 and Miss S. Nicholls maps and views of typical land; > 

 in the Near East. 



It is announced in Science that by the will of Mrs. Jan 

 K. Sacher the University of California is to receive 

 100,000/. The will stipulates that 40,000/. is to be spent 

 on a granite campanile tower, 300 feet in height, to be 

 erected in the centre of the University grounds. An 

 endowment of 100,000/. has been secured, we learn from 

 the same source, by Huron College, in Huron, S.D. St. 

 Lawrence University, too, has obtained a 40,000/. end« 

 ment fund, of which the General Education Board ' 

 contributed 10,000/. Our contemporary also states that 

 the will of Miss J. M. Smith the sum of 1000/. is giv 

 to the .\merican Association for the .Advancement 

 Science. Similar bequests are made to the National G 

 graphic Society of Washington and to the Ameri' 

 Forestry Association of Washington. Other items 

 interest to men of science are 2000/. to the University 

 Pittsburg, 2000/. to the .Allegheny Observatory, and 10 

 to the School of Liberal .Arts and Sciences. 



The Senate of the University of St. Andrews has decii 

 to confer the honorary LL.D. degree, in absentia, u; 

 the following distinguished men, who were chosen for • 

 degree on the occasion of the celebration of the 5c 

 anniversary of the foundation of the University i. 

 September, but were unable to be present on th. i 

 occasion : — Prof. Pietro Blaserna, professor of experiment. 1 

 phvsics in the University of Rome, president R. Accaden 

 del Lincei; Prof. M. j". M. Hill, F.R.S., Astor profe- 

 of pure mathematics. University College, London, 

 lately Vice-Chancellor of the University of London ; Pr 

 Hugo Kronecker, professor of physiology, University 

 Berne; Prof. G. M. Mittag-Leffler, professor of pure mai 

 matics in the University of Stockholm and Rector of t 

 University, founder and editor of Acta Mathematica ; 

 Paul Meyer, directeur de I'Ecole Nationale des Char: 

 Paris, professeur honoraire au College de France ; P: 

 Karl Pearson, F.R.S., Galton professor of eugenics . 

 director of the Laboratory of National Eugenics, Univer~ 

 of London ; Mr. Charles D. Walcott, secretary of the 

 Smithsonian Institution, Washington, U.S.A. ; and Prof. 

 P. Zorn, professor of international law in the Univers' 

 of Bonn. 



