ynly%, 1880] 



NATURE 



225 



Salleion, so that they could be similarly looked at in the 

 direction of the long line of the capillary — the effects 

 weie found almost startling in the brilliancy of the 

 principal lines (chiefly indeed at the red end of the 

 spectrum, for only weak sparks were employed) and in the 

 immense number of additional lines in almost every tube- 

 spectrum examined. These results had been communi- 

 cated to the Royal Scottish Society of Arts in 1S79, 

 before it was ascertained that similar tubes for end-on 

 use in photographing the violet lines had been made by 

 the eminent Dr. van Monckhoven, at Gand, Belgium, 

 three years earlier. But while fully acknowledging the 

 Doctor's undoubted priority of invention, and inviting him 

 to communicate his first published results at one of their 

 meetings, the Society found the case already before them 

 a perfectly independent invention ; a part, too, of a more 

 general system, and accompanied by a series of measures 

 of some of the gas spectra, both in blowpipe flames and 

 spark-illumined tubes, to a greater refinement than had 

 ever been made before. They therefore graciously crowned 

 the paper with a prize and printed it at full length in 

 their Transactions for March, 1879. 



Now some of these increased refinements in knowledge 

 of the spectra of the gases referred to matters long in 

 dispute before the world; and especially to the contention 

 of whether the so-called " carbon-lines'' of some observers 

 seen by them in candle-flames, could possibly be the lines 

 of that most refractory element carbon, or were not rather 

 the lines of some of the very easily volatilised compounds 

 of carbon, unless all the usual chemistry of carbon be 

 utterly at fault. Herein the powers of the aurora spectro- 

 scope with its bright images, its still brighter end-on 

 methods of viewing gas-flames, and its easy powers of 

 rotation from one source of light to another, proved of 

 inestimable advantage ; for not only could large dis- 

 persions, approaching those employed on the sun, be used 

 with effect, but the minutest line in one spectrum could 

 be so cjuickly compared with a similar line in any other, 

 and decided on absolutely as to whether it was or was not 

 in the same spectrum place. 



Wherefore the Edinburgh experimenter proceeded in 

 the following manner : after repeating Prof. Swan's 

 ancient observations and finding with him that all the 

 various hydrocarbons gave more or less comphtely the 

 same spectrum as the blue base of a candle-flame does, 

 he set up for permanent reference, end-on, a blowpipe 

 flame of coal-gas with common air as the best example of 

 that kind of spectrum, viz., the spectrum of a something 

 which vapourises at merely lamp-flame temperature. 

 That that thing could be pure carbon, the chemists one 

 and all declare is impossible, because no furnace heat 

 can vapourise that clement ; but the Royal Society, 

 London, had printed a paper declaring that the unknown 

 agent must be carbon, pure and elemental, because the 

 author of that paper had seen the same spectrum, not 

 only in all combinations of hydrogen with carbon, but in 

 those of oxygen, and also nitrogen, with carbon. This 

 statement too was further strengthened by a Report from 

 the Greenwich Observatory in 1877, to the eflect that 

 gas- vacuum tubes electrically illuminated, having been 

 examined there spectroscopically, no sensible or material 

 difterenccs were found between carbo-hydrogens, carbo- 

 oxygens, and carbo-nitrogens ; the one common spectrum 

 seen there must also, it was argued, though very different 

 from the blowpipe flame spectrum, be the spectrum of 

 pure carbon. 



But as soon as the Edinburgh experimenter tried his 

 end-on vacuum tubes he found an immense difference 

 between carbo-hydrogens on one side, and both carbo- 

 oxygens and carbo-nitrogens on the other ; for the former, 

 though with some other features constant, invariably 

 showed many most brilliant lines in the orange, the citron, 

 the green, and the blue ; while the other tubes either had 

 not any trace at all of those lines, or only so faint a mark- 



ing as to indicate they were there as impurities and not 

 as the whole contents of the so-called "vacuum-tube." 



What were these lines then, so peculiar to carbo-hydrogen 

 tubes .' A reference to the coal-gas blowpipe flame 

 showed that they were its characteristic lines ; the lines, 

 too, of an easily dissociable compound gas therein, and 

 not of an ultimate and most refractory element ; for as 

 soon as the electric sparks illuminating the tubes were 

 somewhat increased in intensity, quantity, and heat, these 

 blowpipe, or we may now safely call them carbo-hydrogen, 

 lines faded out of view ; while the two elements which 

 had made them, viz., pure hydrogen, show-ed its lines, and 

 pure carbon showed, not its ultimate, elemental lines 

 (which nothing short of the most powerful sparks, large 

 batteries, and enormous condensers far above the private 

 means of the Edinburgh experimenter can bring forth), 

 but its low-temperature, compound-linelet, or bank, 

 spectrum. 



Next, on examining the tubes of carbo-oxygen and 

 carbo-nitrogen certain differences between them were de- 

 tected, due apparently to the compound gas in each case 

 being partly dissociated, and partly left untouched, by the 

 simple, small induction-sparks employed. When largely 

 dissociated, then carbon bands and oxygen lines were 

 grandly present in one case, and carbon bands and nitro- 

 gen bands in the other ; with some indications also of 

 the compound's presence in either case, though never to 

 the magnificent degree of the carbo-hydrogen in tubes of 

 that gas. This, however, w^as merely for the simple 

 reason that carbo-hydrogen is by nature a more magnificent 

 "Jighter-up" in luminous spectra ; just as it is indeed the 

 basis of all the means yet adopted in the history of man- 

 kind to correct the darkness of night ; and there seems 

 little chance that science will ever find anything better 

 forevery kind of occasion wherein we now employ candles, 

 gas-lights, and lamps. 



On further examining the carbon bands in the end-on 

 tubes by a dispersion power of 33° from A to H, a pecu- 

 har structure was discovered by the experimenter in their 

 component lines ; and when he found that to be as 

 distinct in a cyanogen tube which contained no trace of 

 either oxygen, or more unusual still, hydrogen impurity, 

 he considered it a proof that that electric spark-raised 

 carbon-band (to which the chemists will probably not 

 object) was the low-temperature spectrum of that element, 

 and not the spectrum, as argued by M. Thalen, of an 

 oxide of carbon. 



Many important points, therefore, seem to be indicated 

 by these experiments, but with the general eflect also of 

 showing that spectroscopy loses much [of its exceeding 

 accuracy in power of discrimination, unless its ob;er\'a- 

 tion be accompanied by some record of the particular 

 '• heat-level " at which the materials examined by it were 

 rendered incandescent. 



Hence a paper on these subjects was communicated to 

 the Philosophical Magazine, London, in August, 1879; 

 and further observations are now being carried on by the 

 same experimenter on a new variety of his end-on tubes, 

 prepared also by I\L Salleron, and giving still brighter 

 spectra than before, with the same electric illumination. 



But all this is only while waiting for the aurora to 

 appear, that phenomenon being the proper cynosure of 

 this particular Edinburgh spectroscope. And now all men 

 trust that the said aurora is soon to reappear, as the 

 multifarious solar activities of a new sun-spot cycle have 

 so evidently begim in the increased size and number of 

 these spots ever since October, 1879; when they were 

 critically considered, and openly announced in Nature, 

 to have at last shaken oft" the languor of their long mini- 

 mum epoch, and to have begun in earnest their prepara- 

 tion for the new series now fairly under way. 



(Since the above paper was written, the first of the new 

 cycle of auroras to come, has been caught. See Nature, 

 vol. xxi. p. 492). 



