ON THE RADIANT HEAT OF THE MOON. | To Professor Tyndall, F.R.S., &c. | Utrecht, January 6, 1865.
SIR,
Allow me to trouble you for your duly and highly esteemed opinion on a subject to which I have given considerable time and care, as you may know from my Changements périodiques de température dépendants du Soleil et de la Lune,2 and from the Annalen3 of Poggendorff. I remember your having written in the Philosophical Magazine*,4 first, that you could not, as Melloni did, find a heating effect from the full moon’s rays by means of your thermoscope, but that, at the same time, you were of opinion that the smoke of London was an obstacle; and secondly, that you supposed that the moon’s rays cleared the sky, and that from that cause the earth lost more heat than it gained by the direct action of the moon. I want to know whether this was a lapsus calami, or your real opinion.
It is very improbable to me that a source of heat should be in any way a source of cold, even if I could admit Sir John Herschel’s opinion to be a true one—that the moon does clear the sky. I could not find, from many years’ observations, that the sky is more serene when the moon is above than when she is beneath the horizon—in other words, that it is clearer about the time of full moon than it is about the time of new moon.
As for the influence on the temperature, I have added together all the observations taken on the first day of the moon, from 1729 till now, as well as all the observations taken on the second, third, fourth, and so on.
The result is not the same from 1729 to 1789 as it is from 1789 to now. In the first period I found a greater sum of temperatures for the days between the 12th and 26th than for the 27th, 28th, 29th, 30th, and the eleven first days. In the second period I find just the same as Mr. Park Harrison,5 viz. a more elevated temperature about new moon; this is also the opinion of the observers who accompanied the late polar expeditions.
The whole series gives, however, a sum in favour of the full moon, just as it ought to be.
You will agree with me that if the new moon really gives a more elevated temperature at the surface of the earth than the full moon, the question is still more interesting, because the opposite ought to be the case, since the whole earth necessarily contains more heat about the time of full moon than about the time of new moon. I have thought, at the same time, whether the moon, when it has north declination, imparts a more elevated temperature to our thermometer than when it has south declination; and I found it to be so; but the difference is equally variable and small.
Now we all admit that other perturbations, a thousand times as great, may totally eclipse for a considerable time the small influence of the moon; but nevertheless it seems to me, when we have 135 years of continued observation, that those perturbations ought to have annihilated themselves.
Why is the mean result so small and uncertain, while we are so certain of the heating action of the moon? The explanation that has occurred to me is this:—
The moon acts partly directly, and by that part the thermometers are most elevated the second or third day after full moon (the day of the greatest north declination for our latitude); but it also acts in some measure indirectly, by elevating the temperature of the aqueous vapour in the atmosphere. By the latter action the clouds and the air have a more elevated temperature, and contain more heat, about and after full moon; but some days must elapse before those particles of air and cloud reach the surface of the earth. When fourteen days elapse before they reach the surface, they have an action wholly opposed to the direct action, and thus the two parts of the action of the moon are necessarily neutralizing each other, more or less.
Hence it is that experiments at great elevations, such as those of Prof. Piazzi Smyth6 at the Peak of Teneriffe,7 are of the greatest value. It is one instance among many where they are indispensable.
My letter is already too long to give you my numbers. I will publish them, but would like very much to know your opinion before doing so. Probably you have not time and leisure just now to give your attention to this question. Perhaps you may think fit, however, to publish this letter of mine, with verbal correction, in the Philosophical Magazine, together with a few remarks of your own.
Excuse me for thus applying to you; it is in order to fix your attention on the subject and to be instructed by your opinion.
I am, Most respectfully yours, | BUYS BALLOT8
* Vol. xxii. p. 470.
C. H. D. B. Ballot, ‘On the Radiant Heat of the Moon’, Phil. Mag., 29 (1865), pp. 162–3
Christophorus Henricus Diedericus Buys Ballot: Christophorus Henricus Diedericus Buys Ballot (1817–1890), a Dutch chemist and meteorologist known for Buys Ballot’s Law and the Buys Ballot Table. He is most noted for his tracking of large weather system movement and solar rotation observation (CDSB).
Changements périodiques de température dépendants du Soleil et de la Lune: C. H. D. B. Ballot, Changements périodiques de température dépendants du Soleil et de la Lune (Utrecht: Kemink et fils, 1847).
Annalen: C. H. D. B. Ballot, ‘Uber den Einfluss der Temperatur auf die Synaphie’, Poggend. Annal., 147 (1847), pp. 177–320.
written in the Philosophical Magazine: Tyndall, J., ‘Observations on Lunar Radiation’, Phil. Mag., 22 (1861), pp. 470–2.
Park Harrison: probably James Park Harrison (1817–1901), a British church architect, archaeologist, and anthropologist (‘Necrology’, The Periodical, 1 (July 1901), p. 16). Ballot was probably here referring to: J. P. Harrison, ‘Lunar Influence on Temperature as connected with Serenity of the Sky’, Phil. Mag., 17 (1859), pp. 153–62.
Prof. Piazzi Smyth: see letter 2002, n. 8.
Peak of Teneriffe: Tenerife is a large island in the Canary Islands chain. The tallest peak on the island is Mount Teide, which Alexander von Humboldt famously climbed and described.
Following this letter from Ballot, the Phil. Mag. included this note from Tyndall: ‘[In the autumn of 1861 I swept the heavens on several days and nights with my thermo-electric pile, and satisfied myself that this instrument is eminently fitted to examine “the mixed action of our atmosphere and stellar space,” as regards radiation. My observations are referred to in the Philosophical Magazine, vol. xxii. p. 470. I still preserve my little observatory on the roof of the Royal Institution, in the hope of being able to carry out te idea expressed in a note at the page referred to. Until this has been done, any opinion of mine on the questions raised by my distinguished correspondent M. Buys Ballot, would be of little value; but I am glad to see the subject in such excellent hands. It also gives me pleasure to find that M. Poey has recently turned the thermo-electric pile to account in examining the atmosphere of Havana. This zealous observer thinks that his observations regarding the action of aqueous vapour are diametrically opposed to mine: I, however, entertain a strong hope that M. Poey himself will eventually clear up the apparent difference. The experiments demonstrative of the action of aqueous vapour on radiant heat of low refrangibility are, in my opinion, perfectly conclusive.—JOHN TYNDALL.]’ (pp. 163–4).
Please cite as “Tyndall2211,” in Ɛpsilon: The John Tyndall Collection accessed on