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state, we shall then have an exception to the law that incandescent solids give continuous spectra, of which we have only one other example, viz. the spectrum of bright lines obtained by Bahr and Bunsen from glowing erbia. In the case of erbia it is not impossible that the bright lines are really produced by a gas (Huggins and Reynolds, Proc. Roy. Soc. June 16, 1870); and it is by no means improbable that, when a hydrocarbon is burned it is first of all decomposed into its elements, which then combine with oxygen. If this be so, the carbon may exist for the moment in the gaseous state."

The difference to which Professor Piazzi Smyth calls attention between the spectra of compounds and elements (the difference, namely, between Plücker's "spectra of the first order" and "spectra of the second order") is important. It is perfectly true that the spectrum of carbon is a spectrum of the first order, and would, from that evidence, be inferred to be the spectrum of a compound. If, however, this spectrum be caused by a compound, it can only be a compound of carbon with carbon.

XIV. Note on the Spectrum of Carbon.

By Dr. ATTFIELD, Professor of Practical Chemistry to the Pharmaceutical Society of Great Britain.

To the Editors of the Philosophical Magazine and Journal.

N chemistry, when compounds of an element with dissimilar radicals yield similar reactions with a reagent, the reactions are held to be evidence of the presence of the element, even though that element in its free state be a massive metal and those compounds be liquid or even vaporous or gaseous. At least, to the question "who gainsays the deduction?" the answer is, "at present, no one.

In 1862 I showed that gaseous or vaporous compounds of carbon with dissimilar radicals, when ignited by the aid of the chemical force in flames, or by the electric force in tubes, or in certain cases by either force, yielded identical spectra; and therefrom I inferred that the spectrum was that of carbon, though I could not say whether the carbon was free or combined in the gases and vapours. And who gainsays the deduction? Mr. Piazzi Smyth, Astronomer Royal for Scotland, in the current Number of the Philosophical Magazine (January 1875).

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Mr. Piazzi Smyth regards my deduction as a delusion, a blunder, an egregious error, a myth, a mistake patronized, he says, by the Royal Society through secret committees, which he designates accursed things, acting occasionally "as very dragons to keep out any salutary doubt expressed on a favoured topic.”

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These are strong terms, especially when penned by an Astronomer Royal, and with the deliberation involved in the circumstances of serial publication. Very strong experimental evidence obtained by himself would surely scarcely justify an Astronomer Royal in the employment of such terms. Yet (will it be believed?) not a tittle of such evidence is forthcoming. Nay, the spectrum which I stated to be that of carbon, a statement confirmed over and over again by eminent chemists and physicists (Plücker, Morren, Marshall Watts), Mr. Piazzi Smyth asserts is not only not that of carbon, but solely that of a hydrocarbonagain an assertion unsupported by any experimental evidence whatever. It is true that Mr. Smyth quotes Lielegg and Crookes against me. But Lielegg supports me, and Crookes is cited because of an editorial footnote in the 'Chemical News' appended to a notice of Morren's paper, asking experimentalists what they meant by the "vapour of carbon" existing in a flame. As for Lielegg, I will quote without comment the last sentence but one of his paper (Eng. trans. in Phil. Mag. March 1869, p. 216:— "Therefore tubes filled with combinations of carbon and hydrogen show the lines of carbon and those of hydrogen; tubes filled with carbonic oxide or carbonic acid gas show those of carbon and oxygen, giving, in fact, a spectrum of carbon, because the extremely small pressure and the high temperature cooperate in reducing the carbon to a gaseous condition." Plücker, who, with Faraday, General Sabine, and Geissler, spent two or three hours with me at the Royal Institution minutely examining my spectra-Plücker afterwards writes, on Nov. 12, 1862: "Je suis d'accord avec vous sur l'existence du spectre de la vapeur de carbone." Morren says, on page 6 of the paper already mentioned, "Je me mis donc au travail avec la pensée préconçue de combattre l'assertion émise par le savant anglais; mais il résulte, au contraire, des expériences auxquelles je me suis livré, que M. Attfield a raison, et que c'est bien la vapeur du carbone qui donne le spectre indiqué plus haut."

I might just refer to some minor statements made by Mr. Piazzi Smyth. He says, in a paper to which he draws attention as not having been accepted, as he desired, by the Roysl Astronomical Society, but afterwards printed in the 'Observations' of his own observatory, that the question put by Crookes was never answered. I answered it at once, and the reply was inserted in the Chemical News' a fortnight after the question was asked. I did not work "in a rich London laboratory." With ordinary induction-coils, borrowed, the one from a captain in the army, the other from Mr. Gassiot; with a spectroscope which Dr. Frankland would scarcely now own; with tubes and apparatus made by my own hands, and made, I believe chemically clean; and by the aid of well-fitting shutters in an ill-fur


nished room-under these conditions only did I carry out my research on the spectrum of carbon. The absence of Plates and measurements in my paper is not ".... explained (in a memoir crowned by being printed in the Philosophical Transactions of the Royal Society of London) by its one chief burden (viz. putting pure carbon vapour for hydrocarbon) having been grateful to the then already formed prejudices of the secret committee who passed it," but by the fact stated in my paper, that Professor Swan had already measured and recorded, confessedly with great accuracy, the position of the lines of the spectrum (observed by him in hydrocarbon flames*).

Spectral analysis brings to light marvellously minute traces of matter, traces difficult to remove even from the surfaces of apparatus, and still more difficult to extract from large volumes of other matter. Have I overlooked traces of hydrocarbons in some of my flames and tubes? Scarcely; for I adopted all precautions known to chemists to obtain chemical purity and cleanliness. Again, other chemists, armed with prejudice against my conclusions, have ended by confirming those conclusions. Still here perhaps is room for sound original investigation; something new could hardly fail to be discovered by eyes trained to observe. Is it too much to expect that a gentleman occupying so high a position as Mr. Piazzi Smyth will either support his statements by such sound evidence or withdraw them altogether†?


XV. On the General Theory of Duplex Telegraphy.

[Continued from vol. xlviii. p. 138.]


HE first part of this investigation concluded by giving (Phil. Mag. vol. xlviii. p. 138) the best relations between * Had so good an observer as Swan worked, instead of the writer, in 1862, with the light just then shed on spectroscopy, I am sure he would have looked for the spectrum in flames not containing hydrogen, and would thus have discovered what I discoved, the spectrum of carbon.-J. A.

†The tone of Mr. Piazzi Smyth's communication renders desirable on my part an expression of regret that my duties in the department of chemistry to which I was appointed within a month of the publication of my research on the spectrum of carbon, have quite prevented me from carrying on similar researches. That regret is much tempered, however, by my belief that such work would have been done far less efficiently by me than by men like Plücker, Morren, Lielegg, Troost and Hautefeuille, and Marshall Watts. I am obliged to add that nevertheless my labours, from the promotion of original investigation in other directions, have neither been few nor unsuccessful. This is the only notice I can take of the personalities in Mr. Piazzi Smyth's paper.-J. A.

From the Journal of the Asiatic Society of Bengal, vol. xliii. part 2, 1874 (read on the 4th of February, 1874). Communicated by the Author.

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the resistances of the different branches of the bridge arrangement-under the limiting supposition, however, that the line used for duplex working was perfect in insulation, or, more generally, that the real conduction-resistance of the line could be neglected against the resistance of the resultant fault*.

It now remains, therefore, to investigate if the simple relations given are generally true; or if not, what they become in case the line has an appreciable leakage. In fact this is clearly the case of practical importance; since all overland lines, especially long ones, even if constructed on the best known principles, will always have a very considerable leakage; i. e. the resistance of the resultant fault (i) will generally be by no means very large in proportion to the real conduction-resistance (L) of the line.

In order to obtain the best general solution of the problem, we must conduct the investigation with great caution; that is, we must be careful not to introduce beforehand any relation between the different variables, however convenient, that is not necessarily a consequence of the paramount condition to be fulfilled for duplex telegraphy, i. e. regularity of signals.

Thus it will be seen that the present general investigation must be conducted somewhat differently from the special one given in the First Part.

It must, however, be understood from the beginning that, whatever the best relations may be which should exist between the different resistances of the bridge method when used on an imperfect line, these relations must revert to the special one given before if we put i=0; and this fact affords a certain check upon the correctness of the new relations to be found.

General solution of the first problem for the Bridge Method.

The annexed diagram (p. 110) represents the general case; and to it therefore I shall refer in the present paper.

The general mathematical question which is to be solved for duplex telegraphy has been stated as follows:

REGULARITY OF SIGNALS.-D and S are two functions which must be rigidly equal to zero when no variation in the system occurs ~and which for any given variation in the system must be as small as possible, and approximate rapidly towards zero as the variation in the system becomes smaller and smaller.

Further, these two functions D and S were expressed, say for station I., as follows:


EN" 1 A'




E′′N'μ' m'f' *For a definition of the terms resultant fault," "real conduction," measured conduction," ‚""real insulation," "measured insulation," &c., which will be of frequent occurrence in this paper, see my 'Testing Instructions,' Part II. Section I.

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These two expressions are quite general; i. e. they do not as yet contain any restrictive conditions (beyond those involved by




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K, telegraph-key of peculiar construction, to be described hereafter. 9, the receiving-instrument connected up in that branch of the bridge which, when measuring resistances, would contain the galvanometer.

a, b, and d are the branches of the bridge.

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f, the resistance between the rest-contact of the key and earth.

w, an additional resistance to be inserted in the battery-branch, for reasons to be given further on.

i, the resistance of the resultant fault ("real absolute insulation" of the line) acting at a distance l' from station I. and at a distance l" from station II. (both ' and l" expressed in resistances so that l'+l"=l equal the "real conductor resistance" of the line).

the mode of arrangement of the system of conductors) between the different variables; and the signification of the abbreviated terms can be found from the First Part*.

*For convenience of reference, I shall give here all the terms of which use will be made hereafter.



These expressions have been obtained by the application of Kirchhoff's rules to the bridge arrangement as represented in the diagram; and they are quite general, as no other relations beyond those represented by the diagram have been introduced as yet.

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