47^ 



NATURE 



[August 9, 191 7 



not the only one available in the application of Ruther- 

 ford's method of computing the age. There is quite 

 as good evidence that the thorium series ends in an 

 isotope of lead as there is for the same conclusion 

 respecting the uranium series. 



Now, in dealing with the atomic weight of the lead 

 found in Ceylon thorite, Prof. Soddy recently carried 

 out,, on a large scale, a very careful chemical analysis 

 of this mineral, and determined the quantity of lead pre- 

 sent. When we calculate, on the basis of his results, 

 -the age of th2 mineral, we get about 140 millions of 

 years. The rocks to which this determination applies 

 are very ancient— ^:ertaifily pre-Cambrian. The result 

 is, therefore, in good agreement with the conclusion 

 derived from denudation. Is this a mere coincidence? 



Before this recent result it was known that the 

 indications of thorium-derived lead were opposed to 

 those of uranium-derived lead, and those who upheld 

 the longer age urgred that the lead derived from 

 thorium must be unstable, and must turn into some- 

 thing else over geological time. But the view that 

 thorium lead is not permanent is one beset with diffi- 

 culties. 



From this we see that the uranium and the thorium 

 families of elements give, at the present time, con- 

 tradictory evidence respecting the age of the earth. 

 The latter apparently agrees in a remarkable manner 

 with the indications of the surface changes of the 

 globe ; the former does not. And now the measure- 

 ments of the uranium halo admi^ of the interpretation 

 that they indicate the failure of uranium-derived lead 

 as a true indicator of geological time. For if the 

 range of U, was, indeed, in remote times longer than 

 it now is, then we must suppose that its rate of decay 

 was at that period faster than it is to-day. Or we may 

 suppose that, however derived, in remote times rela- 

 tively short-lived uranium isotopes existed which have 

 died out during geological time. I am far from con- 

 tending that this view is free from difificulties. On 

 the other hand, our ignorance of the mode of origin 

 of radio-activity and of its possibilities is very consider- 

 able. 



If we have to admit that the evidence of the halo on 

 the age problem is not yet complete, we can refer to 

 a still more important matter upon which the testi- 

 mony of the halo admits of no uncertainty. Until the 

 radio-active origin of halos was ascertained it was 

 impossible to pronounce on how far, in remote periods 

 of earth-history, radio-activity might have affected the 

 chemical elements. Thus it would have been a quite 

 allowable speculation to suppose many of the elements 

 to have been derived as end-products of radio-active 

 families the activity of which has only comparatively 

 recently become extinct. The halo enables a very 

 general answer to be given to such speculations. A 

 substance such as brown mica — and this is one of the 

 most widely diffused of rock minerals — is sensitive to 

 a radiation, and integrates its effects with the same 

 . certainty as the photosensitive plate integrates the 

 effects of light. A mineral containing a minute trace 

 of a radio-active substance beams, throughout the 

 ages of geological time, upon, the medium in 

 which it is contained. If the medium is sensitive the 

 accumulated effects in general persist for our inspec- 

 tion, and in the halo we are, in consequence, able to 

 identify the presence of quantities of radio-active sub- 

 stances of almost inconceivable minuteness. Imagine 

 that stellar magnitude which would be recorded upon 

 a photographic plate exposed uninterruptedly for scores 

 of millions of years ! 



We see from this that the unaffected plate of mica 



is evidence for the absence of even the feeblest a 



radiation from surrounding or included elements, just 



as the blank photosensitive plate is proof of the 



NO. 2493, VOL. 99I 



absence of luminous influi-nce. No definite halo-pro- 

 ducing effects have been observed other than those 

 which may be referred to tl^e known radio-active 

 elements. 



Thus we find that the study of the conditions which 

 call the halo into existence affords a criterion for 

 determining the absence of any general elemental 

 evolution during the period of geological time. When 

 geological time began any earlier evolutionary process 

 must have already come to an end, with the sole 

 exceptions of the known families of radio-active sub- 

 stances. This result, which is a priori by no means 

 evident, is of importance to our views on the physical 

 history of the earth. Only from the minute hiero- 

 glyphics we have been considering could such informa- 

 tion have been derived. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



Oxford. — ^The Rhodes trustees have decided to make 

 a grant of loooL towards the fund which is being 

 raised for the endowment of a permanent professor- 

 ship of forestry in the University, and the trustees of 

 the University Endowment Fund are allowing the 

 payment of 250L per annum, which they have hitherto 

 made towards the payment of an assistant professor, 

 to be carried this year to the professorship of forestry 

 fund. 



A CHAIR of zoology has been established in the 

 University of Manitoba, Winnipeg, and applications 

 for the filling of it are invited. 



The following bequests have been made to American 

 educational institutions by Col. O. H. Payne : — 

 2oo,oooL each to Yale University and the New York 

 Public Library; ioo,oooL each to the Cornell Univer- 

 sity Medical College and Phillips Academy, Andover, 

 Mass. ; 40,000^. each to Hamilton College, Clinton, 

 N.Y., and the University of Virginia. 



The Ellen Richards research prize, value 20oi>, is 

 offered by the Naples Table Association for Promoting 

 Laboratory Research by Women for the best thesis 

 written by an American woman embodying new ob- 

 servations and new conclusions based on independent 

 laboratory research in biology (including psychology), 

 chemistry, or physics. The competing essays must be 

 received before February 25 next. Application forms 

 are obtainable from Mrs. A. W. Mead, 823 Wayland 

 Avenue, Providence, R.I., U.S.A. 



Lord Haldane presided at a meeting of University 

 Extension students at Oxford on August 6, and de- 

 livered an address in which he urged that in educa- 

 tion, as in most other things, unless we have a devolu- 

 tion of powers to those who are able and willing to do 

 the work in the various localities, we shall not make 

 very much progress. He suggested the inauguration 

 of from seven to ten educational provinces in Great 

 Britain. The general object should be to break down 

 the gulf between elementary and post-elementary edu- 

 cation. They should be unified into one great organic 

 whole of national education, and the universities should 

 exert a permeating influence in every province — no 

 province without a universitv at one extreme, and re- 

 presentatives of the local education authority at th^ 

 other. The best men in the locality should be co-opted 

 on the provincial councils, and the teachers, secondary 

 and elementary, should also have an important place 

 on them. The Board of Education should give as 

 much latitude as possible to the provincial authorities. 

 If we can get rid of the network of rigid regulations, 

 we shall have got a great de^l done. 



