October 25, i 906] 



NA TURE 



635 



"it appears not unlikely that many of the so-called 

 chemical elements niay prove to be compounds of helium, 

 or, in other words, that the helium atom is one of the 

 secondary units with which the heavier atoms are built 

 lip. In this connection it is of interest to note that many 

 iif the elements differ in their atomic weight by four — the 

 aloniic weight of helium. 



" If the a particle is a helium atom, at least three 

 a particles must be expelled from uranium (238-5) to re- 

 dtiip its atomic weight to that of radium (225). It is 

 known that five o particles are expelled from radium during 

 its successive transformations. This would make the 

 aiomic weight of the final residue 225 — 20 = 205. This is 

 very nearly the atomic weight of lead, 206-5. I have for 

 siinie time considered it probable that load is the end or 

 final product of radium. The same suggestion has recently 

 been made by Boltwood." 



Then follows a discussion of the evidence on which this 

 •.iKjgrstion is based. 



I think that the above quotation makes my position clear 

 ■ in this subject. K. Rutherford. 



McGill University. Montreal, October 11. 



Radium and Geology. 



The Hon. R. J. Strutt has advanced weighty reasons 

 in favour of supposing radium to be confined to a certain 

 shallow layer over the surface of the earth. To assume, 

 however, that a heavy element is thus restricted in dis- 

 iril)ution appears to me to present difficulties. It would 

 appear that an a priori probable reason why uranium 

 should disintegrate more rapidly near the surface than at 

 greater depths would bridge over the difiiculty, and, if for 

 I hat reason only, would deserve attention. 



1 think such a reconciliation of observational facts with 

 the- probabilities involved would be found in the view that 

 the break up of uranium is not entirely spontaneous, but is 

 partly secondary in character, i.e. that disruption of an 

 a particle from an unstable atom may precipitate the 

 failure of neighbouring atoms, as Prof. J. J. Thomson 

 has suggested might happen in the case of radium. If 

 this be the case, and we assume that the uranium is in 

 general distributed in random aggregates throughout the 

 earth, a reason is at once forthcoming for Mr. Strutt's 

 results. The lighter constituents in the outer crust — 

 aluminium, silicon, oxygen — exert a lesser screening action 

 than the heavy metals deeper down. The conflagration is, 

 as it were, isolated where the heavier metals interpose to 

 absorb the energy of the a ray which initiates the changes 

 leading to radium. It is probable that if the absorption is 

 adequate to reduce the kinetic energy below a certain 

 critical amount, there would be no propagation of disrup- 

 tion. 



The remarkable fact observed in Mr. Strutt's experi- 

 ments that radium is more abundant in the heavier silicates 

 of plutonic rocks than in the lighter is not opposed to 

 this view, but rather in keeping with it ; and the absence 

 of detectable radium in metallic meteorites need not be 

 occasioned by the absence of uranium, but by the slower 

 breakdown of the latter. 



I cannot claim to speak authoritatively on the literature 

 of this subject, but I can recall no other experiments bear- 

 ing on this matter than those quoted bv Prof. Rutherford 

 in the last edition of his " Radio-activily." The case of 

 uranium does not appear to have been investigated. Prof. 

 Rutherford records an experiment in which he dissolved 

 some pure radium bromide in 1000 times its bulk of a 

 solution of barium chloride, and found no change in the 

 y radiation. I venture to suggest that this experiment is 

 not conclusive. Increasing the volume 1000 times increases 

 the average distance of the molecules but ten times, even 

 were these fixed in the medium. This leaves the inter- 

 vening distances still of the order of millionths of a centi- 

 metre. The heaviest metal brought to such tenuity would 

 exert no appreciable screening influence, even from the 



rays, to say nothing of more penetrating radiations. Mr. 

 Eve's experiments, which are also quoted bv Prof. Ruther- 

 ford, are not, I think, to the point. 



.\s cosmical effects of the greatest interest are involved, 



1 think the question of how far radio-active effects are 



NO. 1930, VOL. 74I 



spontaneous deserves full investigation, and I think more 

 especially with regard to the primary step, the generation 

 of radium from uranium. If this is dependent on the 

 matri.x and on concentration, entirely new considerations 

 arise. 



It is not impossible, in the present meagre state of our 

 knowledge, that the penetrating radiations observed at the 

 surface of the earth have to do with the genesis of radium 

 from uranium, the failure of such rays to penetrate deep 

 into the crust limiting the production. The suggestion is 

 continuous with that advanced above. J. JoLV. 



Geological Laboratory, Trinity College, Dublin. 



In reply 10 .Mr. O. Fisher's interesting letter of 

 Octoix r J 1 in this Journal under the above heading, it 

 may be- suggested that, though a state of stable thermal 

 equilibriimi exists now in the earth, it did not in the 

 past, and that the earth has cooled down from a great 

 initial temperature. We are, however, met with this 

 difficulty, that the movements of the crust have been 

 enormous in late geological times, as shown in the great 

 mountain ranges of Tertiary date. This seems to be a fact 

 entirely antagonistic to the suggested explanation. 



No doubt some of the current geologico-dynamic theories 

 will go to the wall should Mr. Strutt's interesting re- 

 searches be confirmed, but I am of opinion that his work 

 will ultimately prove helpful to sounder ideas of the origin 

 of earth structure. T. Mei.i.akd Ri-:,\i)I-. 



Park Corner, Blundellsands, October i-). 



Tm-; age of the great mountain ranges mentioned above by 

 Mr. Reade, though comparatively late, is much earlier than 

 that of the changes of vertical level investigated by Prof. 

 Hull and Dr. Spencer to which I referred. They are 

 evidenced by the drowned plains bordering the .-Atlantic on 

 both sides, and by the deep canons in them which are the 

 continuations of existing river channels. These changes 

 of level are considered to be of Pliocene or early Pleistocene 

 date, and, therefore, geologically very recent. Godwin 

 Austen came to a similar conclusion about the English 

 Channel. 



I thank Mr. Strutt for noticing (p. 610) my letter in 

 N.^TURE of October 11. The fact of uranium not having 

 been recorded in analyses of the rocks, as referred 10 by 

 Mr. Strutt, has occurred to inyself. but not being a chemist 

 I have not alluded to it. But it seems to me that there 

 ought to be an appreciable store of uranium present, large 

 in proportion to the radium it is producing, if the latter is 

 not permanent. That there is not appears to indicate that 

 the disintegration of the radium, and therefore the escape 

 of heat from it, is in some way checked in the earth's 

 crust, as suggested by Mr. Rudge in his letter to the Times 

 of August 18, and that consequently the temperature 

 gradient is not due to radium in the crust, but to the cool- 

 ing of the interior. I think it is in this direction that we 

 must seek for a reconciliation between radium and geology. 



Graveley. Huntingdon, October i<i. O. Fisher. 



Meteorological Data. 



I SII.\LL bo glad if you will enable me through your 

 columns to make known to those interested in the collec- 

 tion of meteorological data the following information. 



A number of copies of the Cape of Good Hope Mag- 

 netical and Meteorological Observations, vol. ii., " Meteor- 

 ological Observations, 1841-6, " have been placed at my 

 disposal by the Controller of H.M. Stationery Office for 

 distribution. The volume contains hourly observations, for 

 each day. of pressure, temperature, and humidity, with a 

 journal of other meteorological data. 



I shall be glad if any scientific institution or library 

 which desires a copy will be good enough to communicate 

 with me upon the subject at the Meteorological Office, 

 63 ^'ictoria .Street. 



I have also available for distribution in a similar manner 

 a few copies of the following works : — 



" Meteorological Observations taken during the Years 

 1829 to 1852, at the Ordnance Survey Office. Phoenix Park, 

 Dublin, . . . and Other Places in Ireland." 



