MOON SUPERSTITIONS.
(Vol. viii., pp. 79. 145.)
Notwithstanding the authority upon which Mr. Ingleby founds the assertion, that there is not the "slightest observable dependence" between the moon and the weather, the dictum is open to something more than doubt. That the popular belief of a full moon bringing fine weather is not strictly correct, is undoubted; and the majority of the popular ideas entertained on the influence of the moon on the weather are equally fallacious; but that the moon exerts no influence whatever on the changes of the weather, is a statement involving grave errors.
The action of the moon on meteorological processes is a highly complex problem; but the principal conclusions to which scientific observations tend, on this matter, may be pointed out without perhaps encroaching too much on the space of "N. & Q."
Luke Howard, of Ackworth, several years ago, concluded, from a series of elaborate observations, extending over many years, that the moon exerted a distinct influence on atmospheric pressure: and Col. Sabine has more recently shown, from observations made at the British Magnetical and Meteorological Observatory at St. Helena since 1842—
"That the attraction of the moon causes the mercury in the barometer to stand, on the average, .004 of an English inch higher when the moon is on the meridian above or below the pole, than when she is six hours distant from the meridian."—Cosmos, vol. i. note 381, (author. trans.); Phil. Trans., 1847, art. v.
Luke Howard farther gives cogent reasons, from his tabulated observations, for the conclusion that the moon has an appreciable effect upon the weather, exerted through the influence of its attraction on the course and direction of the winds, upon which it acts as a marked disturbing cause; and through them it affects the local distribution of temperature, and the density of the atmosphere. There is no constant agreement between the phases of the moon and certain states of the weather; but an apparent connexion is not unfrequently observed, due to the prevalence of certain winds, which would satisfactorily account for the origin and persistence of the popular belief: for, "it is the peculiar and perpetual error of the human understanding to be more moved and excited by affirmatives than negatives" (Nov. Org., Aph. 46.). For example, in 1807, "not a twentieth part of the rain of the year fell in that quarter of the whole space, which occurred under the influence of the moon at full" (Lectures on Meteorology, by L. Howard, 1837, p. 81.). In 1808, however, this phase lost this character completely.
A more marked relation is found between the state of the weather and the declination of the moon: for—
"It would appear, that while the moon is far south of the equator, there falls but a moderate quantity of rain with us; that while she is crossing the equator towards these latitudes, our rain increases; that the greatest depth of rain falls, with us, in the week in which she is in the full north declination, or most nearly vertical to these latitudes; and that during her return over the equator to the south, the rain is reduced to its minimum quantity. And this distribution obtains in very nearly the same proportions both in an extremely dry and in an extremely wet season."—Climate of London, by L. Howard, vol. ii. p. 251., 1820.
Still more recently, Luke Howard has summed up the labours of his life on this subject, and he writes:
"We have, I think, evidence of a great tidal wave, or swell in the atmosphere, caused by the moon's attraction, preceding her in her approach to us, and following slowly as she departs from these latitudes. Were the atmosphere a calm fluid ocean of air of uniform temperature, this tide would be manifested with as great regularity as those of the ocean of waters. But the currents uniformly kept up by the sun's varying influence effectually prevent this, and so complicate the problem.
"There is also manifest in the lunar influence a gradation of effects, which is here shown, as it is found to operate through a cycle of eighteen years. In these the mean weight of our atmosphere increases through the forepart of the period; and having kept for a year at the maximum it has attained, decreases again through the remaining years to a minimum; about which there seems to be a fluctuation, before the mean begins to rise again."—"On a Cycle of Eighteen Years in the Height of the Barometer" (Papers on Meteorology, Part II.; Phil. Trans., 1841, Part II.).
It is satisfactory to all interested in this matter to know that "the incontestable action of our satellite on atmospheric pressure, aqueous precipitations, and the dispersion of clouds, will be treated in the latter and purely telluric portion of the Cosmos" (vol. iii. p. 368., and note 596, where an interesting illustration is given of the effects of the radiation of heat from the moon in the upper strata of our atmosphere).
Jno. N. Radcliffe.
Dewsbury.
Not being quite satisfied with Mr. Ingleby's answer to W. W.'s Query, I beg to refer inquirers to the Nautical Magazine for July, 1850, and three subsequent months, in which will be found a translation by Commander L. G. Heath, R.N., of a paper published by M. Arago in the Annuaire du Bureau des Longitudes for the year 1833, entitled "Does the Moon exercise any appreciable Influence on our Atmosphere?" This treatise enters fully into the subject, and gives the results of several courses of experiments extending over many years; which go to prove that in Germany, at all events, there is more rain during the waxing than during the waning moon. Several popular errors are shown to have arisen in the belief that certain appearances in the moon, really the effect of peculiar states of the atmosphere, were the cause of such atmospheric peculiarities; but we are allowed some ground for supposing that this "vulgar error" may have some foundation in "vulgar truth."
G. William Skyring.