430 



NA TURE 



{Sept. 8, 1 88 1 



to-day is, I am assured, but the feeblest of utterances 

 as compared with the heartfelt gratitude and wondering 

 praise that will be the reward of this great thinker in 

 those future times when the very lowliest in the land shall 

 have full grasp of the meaning of his teaching,'' &c. 



On the whole, the " Student's Darwin " deserves to be 

 successful in its object of popularising Mr. Darwin's 

 work. The great bar to its usefulness will be its need- 

 lessly aggressive tone towards religion, which is sure 

 greatly to lessen a circulation which it might otherwise 

 have had. George J. Ro!m.\nes 



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 vianuscripts. 

 No notice is taken of anonymous communications. 



[ The Editor urgently requests correspondents to keep their letters 

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 that it is impossible othenvise to ensure the appearance even 

 of cojnmunicaticns containing interesting and nc-vel facts.\ 



Tebbutt's Comet — Origination of its Proper Light 



While there seems now no doubt that the honour of being 

 the discoverer of the great comet of iSSi belongs without ijues- 

 tion to that life-long and most persevering observer, as well as 

 successful computer, of comets, in Australia, Mr. John Tebbutt, 

 three communications which chance to have arrived here this 

 morning from different countries contain most diverge ideas of 

 the nature of that portion of the comet's light which universal 

 spectroscopic observation proves is inherent to the comet itself, 

 indicating the existence there of carburetted gas of some kind, 

 and is quite distinct from the concomitant weak reflection of 

 solar light. 



1. In Abbe and Chanoine Moigno's Les Mondes for August 

 25, that excellent physicist in Paris, M. Jamin, is represented as 

 staling that the comet's carburetted gas could be rendered 

 "properly" luminous only in two modes, viz., either by com- 

 bustion or electric discharges. "If by combustion," says he, 

 "how did it first take fire? what keeps up the fire perpetually? 

 and how are the materials of the comet kept, in such a fire, from 

 becoming red-hot, and then giving out quite a different spectrum 

 to any that has yet been oliserved?" Wherefore he concludes 

 that the cause of the "proper" light of the comet is the illumi- 

 nation of its constituent molecules by electric discharge, as in 

 the gas-vacuum tubes of our laboratories. 



2. But next comes a pamphlet from that accomplished spectro- 

 scopist and astronomer, Prof. C. A. Young of Princeton, New 

 Jersey, U.S., setting forth that the bands of carburetted gas 

 seen in the comet's spectrum do most admirably and exactly 

 agree with the combustion-bands of coal-gas and air, as seen 

 in a Bunsen-burner or a blowpipe flame, or in the blue base 

 of all carbo hydrogen flames known; while they do, on the 

 contrary, most euiinently, markedly, and distinctly disagi'ee 

 from the bands of the spectra of the same gases as seen in s^as 

 vacuum-tubes when illumined by electric discharge. And this 

 conclusion of the eminent American physicist is confirmed by a 

 pamphlet just received from M. Fievez, the spectroscopic observer 

 of the re-organised Royal Observatory of Brussels ; as was also 

 announced at the very time of the comet's appearance by the 

 present most acutely observing Astronomer- Royal at Greenwich. 



3. What then ! Is M. Jamin's theory of the comet's proper 

 light being entirely due to electrical illumination utterly over- 

 thrown, and the celestial phenomenon given over to a process of 

 combustion, the mere mention of the necessary details of which 

 suflfices to show it ridiculous and impossible? 



4. Not yet, I venture to think. We ought to discriminate in 

 such a ca^e most carefully between electricities of different in- 

 tensities and different temperatures. Something too of that 

 kind, and even much to the purpose of this cometary case, I had 

 the honour of setting forth to the Royal Society, Edinburgh, 

 last year, in a paper which is now being printed for their Trans- 

 actions. For it was shown therein that, ivhen using an induc- 

 tion-coil capable of giving sparks of such intensity as to be five 

 inches long in the open air, a gas vacuum-tube of olefiant gas 

 showed only the carburetted bands which Prof. Young alludes 



to as being absolutely not the bands which the spectrum of the 

 comet exhibited. But when a smaller cod was employed, and 

 more particularly when its outer helix of long thin wire was 

 replaced by another of short thick wire (specially prepared for 

 the experiment), and the sparks thereby lowered in intensity to 

 such a degree as from i"3 of an inch, to be capable of only 

 passing through o'2 inch of air, then, when euiployed to illu- 

 minate the same olefiant gas vacuum-tube, besides the band.s 

 feen before (Imt now more faintly), another set of bands ap- 

 peared, which were exactly tho^e of the combustion of coal-gas 

 and air, of Bunsen burners, blowpipe flames, blue base of all 

 carbo-hydrogen flames, and finally — teste Prof. C. A. Y'oung, 

 M. Fievez, the Astronomer- Royal, W. H. M. Christie, and 

 others — of Tebbutt's great comei of 18S1. 



5. From this condensation of testimonies I presume that no 

 other conclusion is to be drawn than that the electrical dis- 

 charges permeating the whole length of a comet's tail must be 

 .something exceedingly weak in intensity ; — and the gentlemen 

 who'employ electrically lit-up gas vacuum-tulies in their labora- 

 tories must do their spiriting with them in future much more 

 gently, if they would really arrive at w hat goes on in cometary 

 existences. The following exception, loo, duly mentioned by 

 Pri>f. Young, to his general rule, seems to tend in the same 

 direction. For he states "that while the evidence as to the 

 identity of the flame and comet spectra is almost overwhelming, 

 the peculiar ill-defined appearance of the cometary bands at the 

 time of the comet's greatest brightness is, however, something 

 which he has not yet succeeded in imitating with the flame 

 spectrum." 



6. " Certainly not," we may add to this most honest con- 

 fession ; for as the comet's greater brightness near its perihelion 

 pas'-age could hardly be due to anything else than a temporary 

 increase in the intensity of its illuminating electric currents, that 

 would tend to bring out the tube-set of carburetted bands to 

 interfere with, and spoil the neatness and sharpness of, the so- 

 called ^(2W(?-bands, and would certainly imply a quality or tem- 

 perature which does not exist in any known simple flame, but 

 is found in the spark of even the smallest induction coil, unless 

 some special means are taken to damp down its intensity. 



I have long wished at this Observatory to try a whole course 

 of electric illuminations, as of the old friction machine, Holtz's 

 machine, modern dynamo-machine, coils in variety, and what- 

 ever is capable of giving out electricity in anyvi'ible luminous 

 shape ; but the state of miserable starvation in which this Royal 

 Observatory, Edinburgh, is kept throughout all its branches by 

 Government, and their continued neglect of the applications of 

 their own " Board of Visitors" to "endeavour to obtain justice 

 to this Observatory "—the very words of the l.nst public remit 

 from the Board-meeting, of which the venerable Duncan 

 McLaren, then M.P. for Edinburgh, was chairman — prevent 

 any important apparatus being purchased, or even obtained on 

 loan, to prosecute the inquuries which the science of the times 

 demands. PiAzzi Smyth, 



Astronomer- Royal for Scotland 



Royal Observatory, Edinburgh, August 29 



Schaeberle's Comet 



Since my last remarks I have had an opportunity to examine 

 this fine object with the 6" Cooke equatorial. On Wednesday 

 evening, the 24th, simultaneously with the Great Bear stars, it was 

 easily seen as soon as twilight set in, near the horizon and consider- 

 ably more to the west than on the 21st. With a comet eyepiece 

 it presented, in spite of its low aUitude, a sharp and well-defined 

 figure. The nucleus was stellar-like, with, I thought, a still 

 brighter minute centr.al point. No jets of light proceeded directly 

 from it, but it appeared surrounded by a circular nebulosity of 

 greater extent than the base of the tail, and giving the headed 

 form to the comet frequently seen in old drawings of these 

 objects. The tail was straight, long, and luminous, with a 

 central ray of condensed light which gave it a cylindrical look. 

 When firs't examined three small stars were involved in the tail 

 without any apparent diminishing of their brightness ; while two 

 others below served to define the limit of the tail's visibility in 

 the comet eyepiece. This measured two degrees only, but 

 both it and the nucleus were of a peculiarly fine pale blue 

 tint. I send a drawing of the telescopic appearance of the 

 comet at 8h. 40m. On the nights of the 27th and 2Sth the comet 

 was again examined at about 8h. 30m. Under a lower power 

 Kelhier the appearance was that of a round comet with a central 



