NA TURE 



[December 14, 1905 



currency to a branch of physical science, while in the 

 mining industry the results would possess a fundamental 

 significance. For the first time in the history of 

 mineralogical chemistry it is possible, thanks to the re- 

 searches of Boltwood, Strutt, and McCoy, to predict with 

 considerable certainty the percentage of one element 

 (radium) present if the percentage of another (uranium) is 

 known ; and one asks to what this discovery may not 

 grow. 



It s.-ems to me that the individual and his single lifetime 

 is too small a stake for the prize in view. Such a work 

 should be national, and carried on from century to century 

 if necessary ; and what nation has such a right or such 

 a duty as the one in which the subject of atomic disintegra- 

 tion originated? I confess to a feeling of impatience, to 

 the sense of the inadequacy of the single lifetime, in my 

 experiments on such small quantities of gold as I can 

 purchase, when, disintegrating at the same rate, if dis- 

 integrating at all, tons of gold are lying useless in the 

 national bank, their secret — possibly one that it much 

 concerns the race to know — guarded from knowledge by 

 every cunning invention that the art of man may devise. 

 I confess to a sense of indignation that I should have to 

 purchase for my experiments coins and other objects of 

 known antiquity when within the walls of the National 

 Museum lie — mere dead relics as they at present are — one 

 of the finest collections in existence, capable of affording 

 evidence perhaps of a longer history than any dreamed of 

 by the antiquarian, and guarded by those who cannot 

 interpret the cypher, and who, officially at least, are 

 unaware of its existence. I confess to a feeling of mis- 

 giving in starting experiments where, on the scale possible 

 to the individual, the chances are all against their yielding 

 a positive result in a lifetime. Surely considerations of 

 this character, the availability of the national resources 

 and antiquities for the purpose of scientific investigations 

 under due safeguards, and the provision for and care of 

 experiments of long period with great quantities demanded 

 by this new subject, are worthy of the attention of the 

 nation, and of the British Science Guild as its newly 

 formed adviser. Frederick Soddy. 



The University, Glasgow, December q. 



The suggestion which Mr. Murray has put forward 

 (p. 125) in explanation of the constancy of association of 

 lead and silver has occurred to me also, and is indicated 

 in an article which will probably appear shortlv in the 

 " Jahrbuch der Radioactivitat und Elektronik"; some 

 calculations are contained therein which may be of 

 sufficient interest to justify reproduction here. 



Some recent experiments ' have afforded evidence that 

 the .n tivity of the ordinary metals is caused by the emission 

 of a. particles. On tin:- assumption that these a particles 

 have an ionising power similar to that of those from radio- 

 active elements, it appears that lead should emit less than 

 one such particle per second. In order to find the maxi- 

 mum rate of change thai we can attribute to this metal, we 

 will assume that the emission of one such particle involves 

 the breaking up of one atom of lead and the formation of 

 one atom of silver ; thus one atom breaks up per second. 

 Now a gram of lead contains about 4X10 21 atoms, and 



therefcre to transform ten-millionth part of the lead 



would require 4X10" seconds or more than ten million 

 years. Since it would be impossible to detect a smaller 

 proportion than this by chemical tests, I fear that the 

 experiment which Mr. Murray suggests is impracticable. 

 The earth would probably have ceased to be a habitable 

 globe by the time that the lead was ripe for examination ; 

 perhaps we may trust posterity to settle the matter with 

 greater expedition ! 



But the slowness of the change in lead presents serious 

 difficulties to the theory that the silver in galena is a 

 disintegration product. Even so small a proportion as one 

 in ten thousand (3^ oun.es to the ton) would mean that 

 the silver had been accumulating for a thousand million 

 years— a period longer than that usually assigned as the 

 age of the earth. But until we know more of the processes 

 by which deposits of ore were formed, it is impossible to 



1 The accounts of these should be included 

 Philosophical Ma ■ 



arly, 



of the 



NO. 1885, VOL. 73] 



say whether the lead could have retained its silver through 

 all the vicissitudes of its career. I believe that the silver 

 cannot be separated from galena by any physical means ; 

 it nay be so intimately associated that geological pro- 

 cesses cannot affect it; but against this we have to set tin- 

 fact that cerussite often contains much less silver than 

 the galena from which it is obviously derived. But here 

 chemical separation may have taken place involving the 

 passage of the metals into solution. 



I here are problems connected with the " traces of 

 impurity " constantly associated with certain minerals 

 which await solution by some laborious chemist ; it would 

 lie interesting to see whether there is any tendency to 

 proportionality like that which holds between uranium and 

 radium. But the absence of such a relation might be 

 explained on the grounds that radio-active equilibrium had 

 not yet been attained. 



There is one other point to which attention may be 

 directed. Rutherford has shown that the loss of heat from 

 the earth by conduction would be compensated by the 

 energy evoked by radium distributed throughout the mass 

 of the earth in the ratio of 1 to 2X10"; it appears that 

 this amount of energy might be supplied by the disintegra- 

 tion of the actual constituents of the earth even if no 

 radium were present. It is becoming clear that the older 

 estimates of the age of the earth, based on physical data, 

 are wholly erroneous ; but if the radio-activity of all 

 elements can be established rigidly, and the time constants 

 of their decay measured with sufficient accuracy, it may 

 be possible to use the evidence to which Mr. Murray has 

 directed attention to gain some information as to the 

 period that has elapsed since the solidification of the earth's 

 crust. Norman R. Campbell. 



Trinity College, Cambridge, December 10. 



In Nature, December 7, p. 125, Mr. Donald Murray 

 suggests that the constant association of different elements 

 arises from the slow transmutation of one into the other. 

 The idea is certainly a reasonable one, and I presume has 

 long been in the minds of all who have followed recent 

 work. The writer discussed this question last year (Chem, 

 News. 1904, lxxxix., 47, 58, 118), and arrived at Mr. 

 Murray's opinion. 



Now interest in the matter is reviving, perhaps I may be 

 allowed to direct attention to this discussion. 



Kiel, December 10. Geoffrey Martin. 



Action of Wood on a Photographic Plate. 



I have recently seen some photographic plates used at 

 the last eclipse which have on them, not only pictures of 

 the sun, but also pictures of the wood forming the dark- 

 slides in which they had been placed. 



At a former eclipse I understand a similar disaster 

 occurred. It may, therefore, be well for me again to 

 state that wood in contact with, or in near proximity to, a 

 photographic plate, even in the dark, can impress upon 

 the plate a clear picture of itself. 1 This action is much 

 stimulated by high temperature and brilliant sunshine. It 

 can, however, be stopped in several ways ; probably the 

 simplest one would be to make the slides of copper in 

 place of wood. William J. Russell. 



I i.u \ -Faraday Laboratory. 



Magnetic Storms and Aurora;. 



The interesting paper by Dr. Chas. Chree in your issue 

 of November 30 (p. 101) is inaccurate in one particular. 

 He states that the storm of November 12 was not accom- 

 panied by aurora;. My friend Mr. John McHarg, of 

 Lisburn, writes me that " it was fairly prominent, to be 

 -ei 11 easily above the moonlight, the usual type, a steady 

 glow brighter than the Milky YVav, extending half round 

 the horizon and fading off upwards at an altitude of 20°, 

 or 30° in the west 



From that station aurora' were also observed on 

 November 14, 15, 16, 17, 20, 21, 22, 23, 26, 27, and 30. and 

 it is reported also that a bright crimson arch was seen 

 on the early morning of December 1. 



F. C. Dennett. 



6 Eleanor Road, Hackney, N.E. 

 1 Phil. Trans., vol. exevii. p. 281 ; Proc. Roy. Sue, vol. lxxiv. p. 131. 



