NATURE 



[November 3, 1910 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any ^oiher /)art o/ Nature. 

 No notice is taken of anonymous communications.] 



Helium and Geological Time. 



In Nature of October 27 (p. 543) a short notice appears 

 relative to some experiments of Prof. A. Piutti, of Naples, 

 on the occlusion of helium from the air by salts in 

 the act of solidification. Prof. Piutti apparently considers 

 his results as throwing doubt on the figures which I have 

 given for the age of different geological formations from 

 the accumulation of helium in them. I wish to give my 

 reasons for dissenting from this criticism. 



In the first place, it is not clear from Prof. Piutti's 

 description that the gases extracted from his solidified 

 salts contain any more helium than normal atmospheric 

 air. He has not attempted to show, if I understand his 

 description rightly, that there is any selective absorption 

 of helium in preference to the other atmospheric gases ; 

 nor is it at all likely that such a selective absorption 

 exists, for we have no knowledge of chemical affinity 

 between helium and other gases, while, in respect of 

 solubility, it would probably be inferior to them. Again, 

 on account of its low molecular weight, it would, if any- 

 thing, be better able to escape from mechanical retention. 

 But the gases from minerals are in practically all cases 

 many times richer in helium than is atmospheric air. 

 Mere retention of air cannot therefore account for any 

 appreciable proportion of, the helium found. 



There remains the question, also alluded to by Prof. 

 Piutti, of whether helium can have been absorbed from 

 any source in the interior of the earth. I have already 

 discussed this question, as regards igneous rocks, in Proc. 

 Roy. Soc, A, vol. Ixxxiii., p. 298. As regards the bulk 

 of the rock, it is impossible to exclude such an origin, and 

 I have carefully avoided drawing conclusions which might 

 be vitiated by it. My inferences have been drawn from 

 minerals like zircon and sphene, which are immensely 

 rnore radio-active than the rock in general, and immensely 

 richer in. helium. It is without plausibility to assume that 

 the excess of helium in these has any extraneous origin. 



R. J. Strutt. 



Imperial College of Science, South Kensington. 



Pwdre Ser. 



On my return from a field season beyond the reach of 

 periodicals, I have just seen, for the first time, Prof. 

 McKenny Hughes's article on " Pwdre Ser" in Nature 

 of June 23, and the correspondence relating thereto in the 

 succeeding numbers. It may interest your readers to 

 know that a substance of this sort was found by Mr. 

 Rufus Graves (at one time lecturer on chemistry In' Dart- 

 mouth College) at Amherst, Mass., on August 14, 1819, 

 and by him identified with a luminous meteor which had 

 been seen to fall at that spot on the previous evening. 

 His report of the occurrence appeared in the American 

 Journal of Science, vol. ii., pp. 335-7, 1820. The mass 

 of jelly was circular, about 8 inches in diameter and 

 about I inch thick. It was of a bright buff colour, and 

 covered with a " fine nap similar to that on milled cloth." 

 The interior was soft, of an insufferable odour, and 

 liquefied on exposure to the air. Some of this liquid was 

 allowed to stand in an open glass for a few days, when 

 it had entirely evaporated, leaving only a small quantity 

 of a " fine ash-coloured powder without taste or smell," 

 which effervesced strongly with sulphuric acid, but not 

 with nitric nor hydrochloric. 



Mr. Graves's account was noted by Arago in the Annal. 

 de Chimie, vol. xix., pp. 67-9 (182 1), who quoted also 

 several similar occurrences cited in earlier chronicles. It 

 is probable, of course, that Mr. Graves was mistaken in 

 his identification, that the meteor actually fell at some 

 other point, and that the jelly was confused therewith : 

 only because no other unusual substance was found at the ; 

 point where the meteor was supposed to have fallen. Mr. j 

 Graves himself considered that there was " no reasonable 



NO. 2140, VOL. 85] 



doubt that the substance found was the residuum of the 

 meteoric body," but the evidence which he states is hardly 

 satisfactory to the modern, more critical inquirer. 



It seems probable that these jellies are, in general, 

 Plasmodia of some form or forms of Myxomycetes, and 

 that their common identification with falling stars may 

 have its basis in the frequent recurrence of this error into 

 which Mr. Graves seems to have been led. It is well 

 known that visual estimates of the distance of falling 

 stars are almost invariably far too low. If, then, an un- 

 trained observer of a meteor goes next morning to the 

 near-by place where he thought he saw the body fall, and 

 finds there no unusual body excepting one of these Plas- 

 modia, the jelly and the meteor are almost sure to be 

 associated in his mind. Especially is this probable, since 

 the Plasmodia, in general (at least in my experience), have 

 the appearance of having fallen on the grass rather than 

 of having grown there. Edward E. Free. 



United States Department of Agriculture, Bureau 

 of Soils, Washington, D.C., October 17. 



On Hydrogen in Iron. 



At the recent meeting of the British Association at 

 Sheffield, Sir Norman Lockyer referred to the relationship 

 Between hydrogen and iron at stellar temperatures. Some 

 observations of mine, made several years ago, are of 

 interest in this connection. I also note that at the recent 

 meeting of the Iron and Steel Institute, in a discussion 

 on the influence of carbon in iron, it was suggested that 

 the gases known to be present should also receive 

 attention. 



Iron contains ten times its volume of hydrogen, and in 

 many instances 20 volumes of hydrogen ; even 100 has 

 been noted. Iron therefore contains from about 0-013 to 

 0-026 per cent, of hydrogen, 100 volumes equalling 0-13 per 

 cent., all deemed important in metal with like proportions 

 of carbon and sulphur and phosphorus. It is now fully 

 admitted that hydrogen hardens iron, and should there- 

 fore be estimated: i gram frozen H, ice = 7-2 c.c, 

 0-1=0-72 c.c. I note also iron=i c.c. =7-2 gram iron. 

 II 1 1 c.c. of solid H = i/io gram in 100 iron =14-4 c.c. = 

 7 grams per 1000 c.c, and 1000 ordinary pressure = only 

 0-08961 gram. The figures quoted are apparently in 

 accordance with the periodic law, series 1-7. 



As regards the above, more might be said if space 

 permitted. John Parry. 



October 19. 



Research Defence Society. 



In connection with the cases of plague in Suffolk, let 

 me say that this societ}^ has lately published an illustrated 

 pamphlet, on "Plague in India, Past and Present," by 

 Lieut. -Colonel Bannerman, director of the Bombay 

 Bacteriological Laboratory. It gives a full account of the 

 experiments which proved that fleas carry the plague from 

 rats to man ; it also gives a full account of Haffkine's 

 preventive treatment, and of the many thousands of lives 

 which have been saved by this treatrnent. I am sorry that 

 th.' Research Defence Society cannot afford to give away 

 this pamphlet in large quantities, but I shall be happy to 

 send it to any of your readers who will send me seven 

 stamps. I shall also be happy to send copies, on sale or 

 return, to all booksellers. 



Stephen Paget. 

 (Hon. Secretary Research Defence Society.) 



21 Ladbroke Square, London, W. 



British Mammals. 



I AM grateful for your reviewer's good wishes for the 

 success of my book (Nature, October 20). He writes 

 that he has only one fault to find, namely, that a paper 

 of Dr. K. .Andersen's dealing with the authority for the 

 names Nyctalus noctula and N. leisleri is not mentioned 

 anywhere. I beg to state that the title of this paper is 

 given on p. 53. It could not be cited in the synonymy, as 

 the. names Nyctalus noctula and N. leisleri do not actually 

 occur in it. In fact, I believe that my book is the first in 

 which these names occur. 



G. E. H. Barrett-Hamilton. 



