192 



NATURE 



{July I, 1880 



experienced at present on Arctic and Antarctic regions. The 

 cold althon<Jh it might to some extent diminish the snowfall, 

 would dry the air and prevent the temperature of the snow rising 

 to the melting-point. It would not prevent evaporation taking 

 place over the ocean by the sun's heat, but the reverse, but it 

 would pre\ent the melting of the snow on the land during the 

 greater part of the year. 



In places lil<e Fuego and S. Georgia, where the suow-fall is 

 considerable, perennial snow and ice are produced by diametri- 

 cally opposite means, as I have elsewhere shown, viz., by the 

 sun's heat being cut off by clouds and dense fogs. In the first 

 place the upper surface of the clouds act as reflectors, throwing 

 back the sun's rays into stellar space ; and in the second place, 

 of the heat which the clou-Js and fogs absorb, more than one- 

 half is not radi.ated downwards on the snow, but upwards into 

 space. And the comparatively small portion of heat which 

 manages to reach the ground and be available in melting the 

 .snow is in.=-uflicient to clear off the winter's accumulation. 



James Croll 



Artificial Diamonds 



On reading Mr. Hannay's communication to the Royal Society 

 on the production artificially of crystallised carbon or diamond 

 (rrcc. Roy. .Soc, vol. xxx., No. 204, May, iSSo), in the course 

 of which Mr. Ilannay states that he has made eighty experiments, 

 only three of which have been successful. In almost every case 

 his iron or steel vessels, enormously thick in proportion to their 

 small bore, have burst at a red heat or above it, by the pressure 

 of the included hydrocarbon vapour. 



Will Mr. Hannay permit me to suggest to him that if, instead 

 of an enormously thick and difficult to weld up tube, he will 

 inclose his materials in a comparatively thin one and then inclose 

 that in another like tube shrunk on or contracted over the 

 former, and so on to a third, or, if necessary, fourth tube, each 

 possessing an initial tension upon those within it, he may thus 

 obtain compound tubes cither of wrought iron or steel easily 

 welded staunch, and capable of withstanding any assignable 

 amount of internal elastic -Pressure. This is the principle upon 

 which, since 1855, all rilled artillery is constructed. 



The Grove, Clapham Road, June 22 R. Mallet 



A Fourth State of Matter 

 In Mr. Crookes' communication on this subject (Nature, 

 vol. xxii. p. 153) occurs the sentence, " An isolated molecule is 

 an inconceivable entity." This proposition would appear to me 

 to be questionable. For if we cannot conceive an isolated mole- 

 cule, how are we to conceive of two (or more) molecules, i.e., 

 conceive of matter at all? For the conception of two molecules 

 involves the isolation of each in the mind, otherwise surely the 

 two woidd be mentally blended into one. It is further said of 

 a molecule, "Solid it cannot be." May not the external quali- 

 ties ordinarily attributed to a "solid" be said to be those 

 of a body possessing a certain amount of rigidity {i.e., whose 

 parts resist displacement) combined with a certain elas- 

 ticity? Would not these be substantially the properties of a 

 single vortex molecule, ace irding to those who have investigated 

 this subject? For it appears that such a molecule would be 

 (perfectly) elastic, and inseparable into parts. At the same time 

 it would seem that there would bs nothing to prevent it from 

 being harder or more rigid tliau any large scale solid (built up of 

 such molecules ?) with wliich we are acquainted. 



" A fourth state of matter," as it appears to me, is a distinc- 

 tipn which has somethin^; arbitrary about it. If (for instance) 

 the rether be a gas, the n.ean length of path of whose minute 

 molecules is not less than planetary distances — a proposition 

 wliich it might not be easy to disprove directly — then this would 

 l;c a mean path indefinitely greater than that of the molecnles 

 of the most rarefied gas. Would it, hov/ever, be legitimate to 

 rcjard the tether (under this condition) as matter in "a fourth 

 ;ate"? This would seem, in my judgment at least, only to 

 .- implicate the subject unnecessarily. For after all we are con- 

 cerned in such cases with the mere quantitative difference of 

 length of path. S. ToLVER PRESTON 



Loudon, June 2S , 



Auroral Observations 



In order to get nearer, if jnssibic, to the unravelling of the 

 mysteries of the aurora borealLs, I have in the course of the last 



two years endeavoured to procure a great number of observations 

 of this phenomenon in Norway, S.weden, and Denmark. I have 

 succeeded in engaging throughout the above-named countries 

 several hundreds of observers, who, led only by scientific interest, 

 Iiave lent me their assistance, and from whom I have already 

 received a consider.able amount of information. These observa- 

 tions are to be continued, as there is reason to suppose that the 

 aurora borealis in the near future W'iU appear much more fre- 

 quently than has been the case during the last years. Finland 

 and Iceland will also now be drawn within the circle, and it 

 would be most deiirable that similar observations were made also 

 in Great Britain, which country — especially in the maximum 

 years of the appearance of the aurora borealis — certainly would 

 yield characteristic contributions in this respect. I therefore 

 take the liberty to invite friends of science to make such obser- 

 vations in accordance with the system which I have introduced in 

 Sc.indinavia; a schedule for recording observations, along with 

 the necessary instructions, will be sent to any one who, before 

 the end of August, informs me of his name and address. 



SOPHUS Tromholt 

 Bergen, Norway, June Professor of Mathematics 



Other papers in Great Britain are requested kindly to give the 

 above appeal a place in their columns. 



The Hydrographic Department 



As you have been misinformed on several points respecting 

 my connection with the Hydrographic Department, I request, 

 both on public grounds and in ordinary fairness to myself, that 

 you w'iU insert the following corrections of statements in your 

 article on this subject in Nature, vol. xxii. p. 86. 



My tt'Ork on the Norwegian coast has not been "dignified 

 into a hydrographical survey." That work, combined with my 

 knowledge of the Norwegian language, charts, and pilotage, 

 satisfied the hydrographer that I was competent to compile a 

 " Norway Pilot." It is incorrect to represent that I have ever 

 laid claim to anything more than that. 



I have not made a "rude" or "ungenerous" attack on the 

 Hydrographic Department. I have temperately stated facts 

 which cannot be disproved, in the interests of hydrography, and 

 to show the necessity for giving increased strength and efficiency 

 to the department. It is no answ-er to these facts to disparage 

 my own efforts in the cause, or to call me a small and 

 obscure clique actuated by personal motives. The clique to 

 which I belong is small indeed, for it consists only of myself. 

 It may also be obscure, but it is untrue that I am influenced, in 

 anything I may do, by other than public motives and a desire to 

 further the interests of commerce and of hydrography. 



The gravest error into which your informant has led you is the 

 statement that the Hydrographic Department had confided to 

 me, "mistakenly" or otherwise, the "revision of the sailing 

 directions" for part of Norway. I compiled those sailing 

 directions, as expressly stated in the official printed ' ' Advertise- 

 ment," signed by the hydrographer himself, and the depart- 

 ment has done exactly the opposite of what your informant 

 states ; it has refused to allow me to revise my own work, and 

 has consequently published an erroneous light list, which will be 

 followed by an incomplete "Pilot." Against this procedure it 

 is my obvious duty to protest. I am also bound to warn all those 

 whom it may concern of the errors to which the department has 

 deliberately given dangerous publicity. 



The paper read before the Society of Arts brought the dangers 

 along the trade route between England and Siberia to public 

 notice in some detail, and contained other facts relating to 

 neglected surveys and to charts compiled from antique and in- 

 adequate data, which it was right that merchants and seamen 

 should be aware of. If my statements are accurate — and I chal- 

 lenge your informant to disprove any one of them — then the 

 Society of Arts did useful service in accepting my paper. No 

 good end can be gained by calling me names and accusing me of 

 personal motives. Let my statements be disproved if your in- 

 formant is able to disprove them. If he cannot do so, then 

 those statements are incontrovertible witnesses to the fact that 

 the Hydrographic Department is unequal to the demands upon 

 it. Unsupported assertions that the department stands "well, and 

 deservedly so, in the estimation of scientific circles," are of no 

 weight when opposed to facts, which your informant cannot dis- 

 prove, and apparently dares not face. George T. Temple 



The Nash, near Worcester, June 2 



[We have given publicity to Lieut. Temple's reply to the 



