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first and perhaps the only men who could turn it to so good an account. Professor Bunsen's researches are almost as well known in this country as in his own, and from the moment of their publication become the models for all subsequent inquiries in the same subjects. If Professor Kirchhoff's name is here less familiar, it is only because his subjects of study are more abstruse, and less likely to draw the attention of a people who are generally practical in their pursuits.
The earliest observations we have found bearing on this subject were communicated to the Royal Society, in January 1785, by the Rev. M. Morgan.* He examined by the prism the light of bodies in a state of combustion, and mentions the method as if it were nothing new; thus, “if sulphur or æther is burned, or any of those combustibles whose vapour is kindled in a small degree of heat, a blue flame will appear, which, if examined by the prism, will be found to consist of the violet, the indigo, the blue, and sometimes a small quantity of the green rays." He also alludes to a Mr. Melvill's mode of examining bodies whilst on fire by the prism, and the following sentence will prove interesting in regard to the history of the subject: “Mr. Melvill, when he made some of the preceding experiments, observed that the yellow rays frequently escaped in the greatest abundance; but this singularity proceeded from some circumstances which escaped his attention.”† Although this same singularity occurred to all subsequent observers, the circumstances alluded to escaped detection until within five or six years of the present date.
Dr. Wollaston may doubtless be considered the first talented observer in this now important and fascinating branch of science. In the same paper in which he gives the first notice of Fraunhofer lines, he mentions that by candlelight a different set of appearances may be distinguished. Among these is a bright line of yellow. Again, I “ when the object viewed is a blue line of electric light, I have found the spectrum to be also separated into general images; but the phenomena are somewhat different from the preceding. It is, however, needless to describe minutely appearances which vary according to the brilliancy of the light, and which I cannot undertake to explain.” These last remarks lead us to reflect how short is the step in advance which the wisdom even of a man like Wollaston allows him to take, and how great the error of supposing that even the most apparently
• Phil. Trans. vol. lxxv. p. 190.
+ Ibid. p. 194. We know nothing more of this Mr. or M. Melvill, unless he be the same as T. Melvill, the author of a letter on the different refrangibility of the rays of light, in the Phil. Trans. for 1753, p. 261. The letter is dated Geneva, Feb. 2, 1753.
Phil. Trans. (1802), vol. xcii. p. 380.
fickle phenomena of nature will not be reduced to law, and to some useful purpose, by due observation and reasoning.
Among Fraunhofer's observations* were some upon the coloured spectra of flames and the Electric Light, which were published in a supplement to his principal paper.t He noticed a bright orange double line in the spectrum of a lamp, and found it to hold the place where, in the spectrum from sunlight, the dark line D stands. He also found this ray of light, which is, of course, soda light, in the blowpipe flame, and suggested that this simple homogeneous light would be useful in many experiments. This idea was about ten or eleven years afterwards applied by Brewster in the Monochromatic Lamp. So far we find no hint of the principle of spectrum-analysis ; but we come now to mention H. F. Talbot, the chief discoverer of photography, who, thirty-five years ago, recognised and announced the principle with considerable distinctness. The name will be familiar to many from the Talbotype process of photography having been named in his honour by Sir D. Brewster. In 1826 Talbot, at that time a member of Parliament, appears to have occupied himself with a set of rather desultory but clever optical experiments. He analysed light from various coloured flames prismatically, and in the spectrum of the light of deflagrating sulphur and nitre he observed a red ray, also presented by the flame of a spirit-lamp, whose wick had been soaked with nitre or chlorate of potash. He was now led to argue as follows: I
“ This red ray appears to possess a definite refrangibility, and to be characteristic of the salts of potash, as the yellow ray is of the salts of soda, although, from its feeble illuminating power, it is only to be detected with a prism. If this should be admitted, I would further suggest, that whenever the prism shows a homogeneous ray of any colour to exist in a flame, this ray indicates the formation or the presence of a definite chemical compound. An excellent prism is, however, requisite to determine the perfect homogenity of a ray." The concluding paragraph of this paper is as follows:
“ The red-fire of the theatres, examined in the same way, gave a most beautiful spectrum, with many light lines or maxima of light. In the red, these lines were numerous and crowded, with dark spaces between, besides an exterior ray, greatly separated from the rest, and probably the effect of the nitre in the composition. In the orange was one bright line, one in the yellow, three in the green, a very bright one in the blue, and several that were fainter. The bright line in the yel. low is caused, without doubt, by the combustion of the sulphur; and the others may be attributed to the antimony, strontia, &c., which enter into this composition. For instance, the orange ray may be the effect of the strontia, since Mr. Herschel* found in the flame of muriate of strontia a ray of that colour. If this opinion should be correct, and applicable to the other definite rays, a glance at the prismatic spectrum of a flame may show it to contain substances which it would otherwise require a laborious chemical analysis to detect.” (London, March 1826.)
* It is of so much advantage to consult original writings, that we regret the difficulty under which most English readers lie in obtaining access to the memoirs of Fraunhofer and many celebrated continental observers. Fraunhofer's celebrated memoir, with his excellent map of the spectrum, is in the Munich Transactions (Denkschriften der Academie der Wissenschaften in München für die Jahre 1814-15, B v.). A French translation is said to be in Schumacher's Astronomische Abhandlungen, 2 Heft, Altona, 1823. The Life of Fraunhofer, and some part of his writings, will be found in Brewster's Edinburgh Journal of Science, vols. vii. and viii. + Translated in Brewster's Edinburgh Journal of Science vol. viii. p. 7.
Brewster's Edinburgh Journal of Science, vol. v. p. 81.
We do not find that he published any thing further on the subject until February 1834, when he discriminates with considerable accuracy between two substances which have since proved so interesting in the hands of Bunsen. He says:f
“Lithia and strontia are two bodies characterised by the fine red tint which they communicate to flame. The former of these is very rare, and I was indebted to my friend Mr. Faraday for the specimen which I subjected to prismatic analysis. Now, it is difficult to distinguish the lithia red from the strontia red by the unassisted eye. But the prism displays between them the most marked distinction that can be imagined. The strontia flame exhibits a great number of red rays, well separated from each other by dark intervals, not to mention an orange, and a very definite bright blue ray ; the lithia exhibits one single red ray. Hence I hesitate not to say that optical analysis can distinguish the minutest portions of these two substances from each other with as much certainty, if not more, than any other known method.”
It may seem surprising that Mr. Talbot did not follow up the principle which here so clearly suggested itself. To a French or German philosopher it would have afforded subject of assiduous study for years. Perhaps the want of an extensive chemical knowledge prevented him from seeing the whole value of method; but we think that it may have been the extreme delicacy of the soda-test, and the almost universal presence of soda, which quite puzzled Mr. Talbot, and perhaps discouraged him from further prosecuting the method. Thus he found that perfectly clean platinum did not affect a flame, but after being touched with soap, or even with the finger, it produced yellow light. Wood, ivory, paper, and many other substances, when burnt, gave more or less of this yellow light, “which,” he says,
Edinburgh Transactions, vol. ix. P. 456. + Phil. Mag. (3d Series), vol. iv. p. 114.
Brewster's Edinburgh Journal of Science, vol. v p. 79.
“I have always found the same in its characters. The only principle which these various bodies have in common with the salts of soda is water; yet I think that the formation or presence of water cannot be the origin of this yellow light, because ignited sulphur produces the very same, a substance with which water is supposed to have no analogy.”
Here was certainly a difficulty very naively and frankly stated, from which Mr. Talbot never extricated himself. More confidence in the principle he had formed would have led him to assert that, because soda-light appeared, soda must have been present, for this is exactly the principle on which Kirchhoff and Bunsen now announce to us the composition of the sun, and assert the existence of new elements before any one has seen them.
It is not a little curious that, about the same time with Mr. Talbot's experiments, two of the most distinguished physicists of this century, Brewster and Herschel, were likewise experimenting on coloured flames, and both were led into similar error by this evil-disposed soda-light. Thus Brewster, in describing his Monochromatic Lamp for the illumination of objects in Microscopy, by which all chromatic aberration and indistinctness would be avoided, says:*
“It had long been known that a great quantity of homogeneous yellow light was created by placing salt or nitre in the white flame of a candle, or in the blue-and-white flame of burning alcohol. After numerous experiments, attended with much trouble and disappointment, I found that almost all bodies in which the combustion was imperfect, such as paper, linen, cotton, &c., gave a light in which the homogeneous yellow rays predominated ; that the quantity of yellow light increased with the humidity of these bodies ; and that a great proportion of the same light was generated when various flames were urged mechanically by a blowpipe or a pair of bellows."
Knowing, as we now do, that spring-water, rain-water, and even the air itself, are almost never free from traces of soda, the perplexity and despair of the acute Sir David, arriving at a climax in the bellows experiment, are not a little amusing.
Sir J. Herschel,7 too, investigated the nature of these chemical coloured flames; but the curved lines by which he represented the optical types or spectra of lime, baryta, and strontia, bear evidence that this most sound and excellent of natural philosophers was likewise in error about the soda-light. In the flame of sulphur violently burning he noticed perfectly homogeneous light, of a brilliant yellow colour and strictly definite refrangibility
* Trans. of the Royal Society of Edinburgh, vol. ix. p. 435.
It is curious to observe the very different use of these coloured flames which suggested itself to Talbot and to Herschel. The former, calling optics to the aid of chemistry, proposed the method of prismatic analysis, now performing such wonders. Herschel was then an optical philosopher, calling chemistry to his assistance, and his thoughts accordingly took a very different direction. “It is needless,"'* he says, “ to insist on the advantage that may be taken of these and similar properties of coloured flames and media in optical research.”
The next allusion to spectrum-analysis is in 1835, when Professor Wheatstone presented a paper to the British Association, † “ On the Prismatic Decomposition of Electrical Light," describing the spectra observed when the electric spark is taken between points of various metals. In the observations he employed a telescope, furnished with measuring apparatus. He determined that each metal present occasioned bands peculiar to its own spectrum, in perfect independence of any other metals, or of the medium through which the spark is displayed. “The appearances are so different,” it is added, “ that, by this mode of examination, the metals may be readily distinguished from each other.”
In the next place, Dr. W. A. Miller, in the meeting of the British Association in 1845, described the prismatic spectra from flames coloured by copper, boracic acid, strontium, calcium, and barium. No allusion is made to their analytical use, and the spectra, indeed, as given in a coloured print, present but little resemblance to what other observers describe. Perhaps the doctor had some solid substance present in the flame, and omitted to eliminate all rays that do not invariably accompany the element examined.
The “Etudes de Photométrie Electrique” of M. A. Masson now follow in the order of time, in the fourth and fifth parts of which he has described many most interesting observations. He examined the spectrum of the electric spark when taken in air, between poles of various substances, as also in vacuo, in various gases, and in several liquids ; but his results chiefly bear
. Trans. of the Royal Society of Edinburgh, 1823.
* We do not find that more of this paper was published than an abstract in the Philosophical Magazine, a reprint of which is all that appears in the Report of the Association! See Notices of Communications to the British Association at Dublin, August 1835, p. 11. Masson, in a memoir afterwards referred to, also regrets his inability to learn more about Wheatstone's researches; and we must say that a large part of the Association's publications are perfectly useless for reference. The same is the case with the publications of the Association for Social Science. Abstracts have generally no value. (A fuller report of Wheatstone's experiments has, however, very recently appeared in the Chemical News.)
| Phil. Mag. (30 Ser.), vol. xxvii. p. 81.