(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 {322} 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).