Andersenian University | Glasgow | Jan. 13th 1865.
Professor Tyndall
Dear Sir,
Having read most of the articles which have appeared on the subject which you have designated Negative Fluorescence, I felt somewhat surprised at Dr. Akin’s remarks1 in the Philosophical Magazine for December last. Although I consider that you were quite right in replying2 still there does not seem to me to be anything in the subject really worth contending for.
The whole matter appears to be comprehended under the two following particulars:—
1. Heat a platinum wire for example in an oxyhydrogen flame and the wire becomes white hot.
2. The rapid vibrations of the platinum molecules are produced by the slow vibrations of the aqueous molecules constituting the flame.
As regards to No. 1. neither you nor Dr. Akin, of course, claims to be the first observer. But unquestionably you were the first to establish No. 2. For it was your famous experiments on Radiant Heat which proved that the oxyhydrogen flame consists of waves or, rather we should say, vibrations of slow period.
The point however to which most importance is attached is not these facts themselves, but a certain conclusion supposed to be derived from them, viz that when the platinum wire is heated in the oxyhydrogen flame, a change of period, or a conversion of long waves into short ones takes place.—I am sorry to say that I have been wholly unable to perceive the legitimacy of this conclusion. All that I can perceive is simply this; the vibrating molecules of the flame set the molecules of the platinum a vibrating, but owing to some physical difference in the two sets of molecules the one set vibrates more rapidly than the other.
It is certainly an abuse of language to say that because the vibrations of the platinum molecules are more rapid than those of the flame, that there is a change of period, or a breaking up of long waves into short ones.—A blacksmith will render the platinum incandescent by simply striking it with his hammer. But who would speak of a change of period in this case? And yet there is no essential difference between the two cases. In the one case the molecules of the platinum are set a vibrating by the blows imparted by the hammer, in the other case these molecules are set a vibrating by blows imparted by the molecules of the flame. But the molecules of the flame may be justly regarded as so many small hammers striking the platinum. The vibrating molecules of the platinum stand in precisely the same relation to the blows of the hammer, that they do to the blows of the molecules of the flame. And it appears to be just as proper to say that the slow blows of the hammer are converted into the rapid vibrations of the platinum molecules, as it is to say that the slow vibration of the flame molecules are converted into the rapid vibrations of the platinum molecules.
Trusting that you will pardon me for troubling you with these few random remarks
I am, | Sir, | Yours respectfully | James Croll.
RI MS JT/1/TYP/1/65–6
LT Typescript Only
Dr. Akin’s remarks: C. K. Akin, ‘On Calcescence’, 29 (1865), pp. 28–43. This article appeared in the January 1865 issue, not December 1864.
quite right in replying: J. Tyndall, ‘On the History of Negative Fluorescence’, Phil. Mag., 29 (1865), pp. 44–55. This immediately followed Akin’s article. Akin followed up in the March issue with ‘Further Statements concerning the History of Calcescence’, Phil. Mag., 29 (1865), pp. 136–51. This article included a note from editor William Francis that ‘the discussion of this subject must close, so far as our pages are concerned’ (p. 151). On Tyndall’s dispute with Akin, see the introductory essay to this volume for further context and commentary, and letters 1925, 2075, 2076, 2079, 2114, 2162, 2167, 2168, 2170, 2173, 2182, 2183, 2190, 2197, 2198, 2201, 2204, 2208, and 2214.
Please cite as “Tyndall2214,” in Ɛpsilon: The John Tyndall Collection accessed on