76 



NATURE 



\May 22, 1879 



bringing the said Brorsen's comet into line with most other 

 comets, as to possessing both that band and material. 



Secondly, Dr. Watts alludes to Mr. Christie, of the Royal Obser- 

 vatory, Greenwich, having also recently observed the spectrum of 

 the same comet, and stated that he had thereby found the sanie 

 result as Prof. Young. But the Doctor implies there must be 

 some mistake therein, because — what Mr. Christie compared the 

 sharp edge of the comet's green band, with, and found it coin- 

 cident, was not the Buusen gas burner's green band, but that of 

 an alcohol vacuum tube illumined by electric spark ; and this 

 latter green band, he says, is i 1 an absolutely different spectrum- 

 place to that occupied by the coal-gas burner's green band. 



The first answer here, is both pleasant and simple. I know 

 perfectly well what it is the Doctor alludes to, as being visible 

 in t'le alcohol vacuum tube, but would beg to remind an accom- 

 plished laboratory worker that it is so close in spectral place to 

 the coal-gas flame's green band, that in any spectroscope of very 

 small dispersion, and when the subject is seen only faintly and 

 at intervals in a difficult astronomical observation, such minute 

 difference of place might well be disregarded in comparison with 

 the enormous difference or anomaly of an older, almost historic, 

 record, whose large discrepance, eight times larger than the 

 other difference, was really the thing which both Mr. Christie 

 and Prof. Young had before them, either to prove or disprove. 

 And as they have now each of them independently assured us, 

 by special observations at the end of a telescope in the cold 

 night air, that the enormous anomaly suspected of old no longer 

 exists — they both deserve our best thanks. 



But next comes, for those wko work in-doors with brighter 

 lights and more powerful spectroscopes, the second part of the 

 answer, with a proof that Mr. Christie, after all, may not have 

 used a differently placed reference to Prof. Young's, even in the 

 least degree, because, besides what Dr. Marshall Watts says very 

 truly, there is in the spectrum of an alcohol vacuum tube elec- 

 trically illumined, there is also a something else which he either 

 has not seen, or has not yet recognised as such, but which is the 

 vary identical green band of the coal-gas flame in open air. 



The special green band which the Doctor has seen and recog- 

 nised in an alcohol vacuum tube is to be seen equally in vacuum 

 tubes of all gases containing carbon in any combination, and is 

 therefore abundantly visible in tubes of carbon monoxide, car- 

 bon dioxide, and cyanogen. This, too, is the spectrum which 

 he calls the " Carbon spectrum No. 2," but which I call simply 

 the spectrum of carbon ; a spectrum which no one has yet found 

 in any common candle flame, coal-gas flame, or comet in the 

 sky ; and it requires apparently the ecstatic heating of the elec- 

 tric spark for its smallest development. 



But the other green band, which I shall presently prove is also 

 in an alcohol vacuum tube, though the Doctor may not have 

 recognised it there, he has seen abundantly elsewhere, for it is 

 found in the blue base of every candle, lamp, or coal-gas flame, 

 and he has given the spectrum place of the beginning of it with 

 exceeding accuracy. In fact, the only unhappy thing is, that he 

 will look upon it as pure carbon, calling it the "Carbon spec- 

 trum No. I," when it is so evidently the compound "carbo- 

 hydrogen ; " for with my new end-on tubes, while I do not see 

 this green band in vacua of either carbo-oxygen or carbo-nitro- 

 gen (unless ultra-faintly as a trace of impurity), I do see it, and 

 most brilliantly, in tubes of such rich carbo-hydrogens as alcohol 

 and oleflant gas. 



Now it is not a little singular as a coincidence merely, that I 

 was actually engaged only yesterday, after an interval of several 

 years, in pointing out to my friend Prof. Swan, of St. Andrews, 

 the existence of "his" carbo-hydrogen blow-pipe flame's lines 

 of its green band, projected upon, and differently placed from, 

 the true elemental carbon green band ot an alcohol vacuum tube, 

 electrically illumined ; and we proceeded thus to test the identity 

 of what I called "his" flame lines, by a close proof of place, 

 which is everything in spectroscopy. 



A coal-gas and air blow-pipe flame, end-on, was set up before 

 the spectroscope on one side of the table, and on the other side 

 an alcohol vacuum tube, illuminated by i-inch sparks from a 

 small coil, and viewed also end-on. The spectroscope could be 

 rotated easily in azimuth by endless screw motion, so as to look 

 with its gathering telescope -first into the tube, then into the 

 flame, and then again into the tube. The prism train had the 

 large dispersion of 33° between A and H, the telescope a mag- 

 nifying power of 10, and its pointer was one of Mr. Hilger's 

 latest and most refined steel wedges of almost infinite sharpness. 



The slit was made exceedingly narrow, the definition in the 

 centre of the field was super-excellent, and then Prof. Swan mi- 

 crometrically bisected a certain thin but exceedingly bright line, 

 which looked like an anomaly on the surface, and far within the 

 least refracted edge of the elemental carbon green band of the 

 alcohol tube, and clamped the pointer in that exact spectrum 

 place. 



I then rotated the whole instrument round to the blow-pipe 

 flame, and asked him "What is the pointer on now?" 



" On the first and brightest line of the blow-pipe flame's green 

 band," he answered, "Alexander Herschel's green giant of 

 carbo-hydrogen, and it is admirably bisected too. ' 



We next rotated back to the alcohol tube, and found the 

 pointer still accurately bisecting that bright line present there, 

 which was a total anomaly in a pure carbon spectrum, though 

 perfectly agreeable to what Prof. Swan wrote of the compound 

 carbo-hydrogen's flame spectrum, twenty-three years ago. Most 

 opportunely present also in that tube, for it enabled Mr. Christie 

 to compare Brorseu's comet with the same identical reference as 

 that used by Prof. Young, though employing an alcohol spark 

 spectrum, and not a gas-burner. 



The second line of the blow-pipe flame's green band, though 

 much fainter, is also distinctly seen in the end-on view of the 

 alcohol tube's spectrum, and answers perfectly to a similar test 

 for place as the first line. Wherefore, I would beg to ask, how 

 can I hold any other view than that carbon, as a pure chemical 

 element, and the most refractory that is known, has no spectntm 

 short of electric spark temperature ; and what it then shows is, 

 to exact measurement with large dispersion, a perfectly different 

 spectrum to that of the compound gas, carbo-hydrogen'; which 

 compound gas, while still existing to some extent in 'the electric 

 spark tubes, begins its spectral manifestationi in the very mode- 

 rate temperature of merely a farthing tallow candle : a matter to 

 be duly considered in studying the physical condition of comets, 

 which do not show any spectrum (or, for small and "uncon- 

 densed " sparks, we may say the spectrum) of pure elemental 

 carbon. PiAzzi SMYTH 



Edinburgh, May 9 



The Victoria University 



In the article on the Victoria University in the last number 

 of Nature, I observe some inaccurate statements regarding 

 the Queen's University in Ireland. 



In the first place there are no\.four colleges, but three. Next 

 there are no degree examinations in any college, but all are 

 conducted in Dublin by the examiners of the university, who, 

 for the most part, are also professors in the colleges ; but there 

 are some examiners who are not professors, and also some 

 professors who are not examiners. A. J. C. Allen 



Peterhouse, Cambridge 



Maps of Old Geological Coast-lines, &c., &c. 



I NOTICE in Woodward's " Manual of the MoUusca," when 

 speaking of the "Boundaries of Natural History Provinces," 

 p. 352, the following : — 



"The seas are divided by continents and influenced by the 

 physical character of coast-lines, by climates, and currents." 



May not the occurrence of different species in different parts 

 of contemporaneous strata help to determine the positions of 

 land and water, &c., in past geological ages? W. W. 



Cambridge ' 



[In reply to " W. W.'s" interrogatory, "May not the occur- 

 rence of different species in different parts of contemporaneous 

 strata help to determine the positions of land and water, &c., in 

 past geological ages ? " we would say. Yes, most certainly ; and 

 it is not only by recording the occurrence of different species, 

 probably peculiar to different zones of depth, that geologists 

 have long tried to mark out old sea-beds, but more especially 

 by tracing carefully the occurrence of the same species along ex- 

 tended lines of formations, they have attempted to map out old 

 geological coast-lines. Much has been done in this direction 

 by Godwin- Austen, Forbes, Quenstedt, Oppel, Waagen, Hebert, 

 Oswald Heer, and many others ; but much more remains to be 

 accomplished, and " W. W." cannot do better than take up 

 some such line of inquiry for his summer vacations. How 

 much good field-work might be done in three months' holidays 

 in, say, three successive years, with a knapsack on one's back 

 and a hammer in one's hand, let the admirable papers by Dr. 

 Chas. Barrois of Lille teUl— H. W.] 



