it must be so very small that certainly it cannot
authorise weather prophets to found their
predictions upon changes of the moon.

But if the moon will not enable us to foretell
rain or sunshine, she does help us to fix
historical dates and to correct our ancient
chronology.

In an eclipse of the sun, the moon screens
the sun, either totally or in part, from certain
portions of the earth's surface. Here, it is
total or annular; there, it is only partial; further
on, not a trace of it is witnessed. In an eclipse
of the moon, on the contrary, the rays of the
sun are totally or partially intercepted from
the moon by the earth's interposition; and this
privation of light is seen in the same way from
all points of observation.

The ancients (who had nothing like so
precise a knowledge as we have of the moon's
movements) were unable to predict eclipses
of the sun. They foretold lunar eclipses only;
basing their predictions on the fact that those
eclipses are reproduced almost periodically,
presenting the same characters and the same
intervals between each other, every eighteen years
and eleven days. It therefore sufficed to have
observed and registered all the eclipses of the
moon happening during that period, to be able
to announce with certainty the eclipses which
were to occur during the period following.
Now, on the contrary, with the much more
exact information which we possess, not only
of the moon's motions but also of the sun's,
we are in a position to calculate and announce
a great many years and even centuries beforehand,
both the general circumstances of lunar
and solar eclipses, and also all the peculiarities
which the latter will present at any given spot
on earth. In like manner, by a retrospective
examination, we can give an account of all the
circumstances accompanying ancient eclipses in
this or that locality.

Eclipses of the sun are somewhat more
frequent than those of the moon. But as a solar
eclipse can never be visible over so large a
portion of the earth's surface as a lunar eclipse,
it follows that, for any one given spot, solar
eclipses are least numerous. And if, instead
of noting all solar eclipses, we only reckon
those which are total, we shall find that, at
the same spot, they are very far from numerous.
We may even say that, for any determinate
locality, total solar eclipses are veritable rarities.
In Paris, for instance, only one was seen during
the whole of the eighteenth century—the eclipse
of 1724. In the nineteenth century there has
not been, nor will there be, one. The Londoners
were five hundred and seventy-five years without
one total eclipse—from the year 1140 to
1715; and since 1715 they have witnessed no
similar spectacle.

If history mention a total eclipse of the sun
as having been observed at a given spot, without
giving the precise date of the observation, that
date may still be determined by the exact
knowledge we now possess. Recurring to the epoch
to which the phenomenon belongs, we successively
pass in review the different solar eclipses
which occurred during a lapse of years of such
extent, that we are certain it must comprise
the year in which the eclipse in question was
observed. By proceeding in this way we shall
generally find that, out of all those eclipses,
there is only one corresponding to that recorded
in history; because that one only can possibly
have been total at the spot where the observation
was made. We shall thus get, not merely
the year, but the day and even the hour, of the
observation.

Take an example. Herodotus relates (book i.
§74), "After that, the Lydians and the Medes
were at war during five consecutive years. In
this war the Medes frequently vanquished the
Lydians; the Lydians also often beat the
Medes. On one occasion they even fought by
night. Now, as the war continued with equal
chances on either side, in the sixth year, one
day when the contending armies were engaged,
it happened that, in the midst of the strife, the
day was suddenly changed into night. Thales
of Miletus had foretold this phenomenon to the
lonians, indicating the exact year in which it
actually did take place. The Lydians and the
Medes, beholding night suddenly interrupt the
day, put an end to the combat, and thought
only of settling the terms of peace."

The eclipse here referred to, is known as
Thales's eclipse. The various authors who
have mentioned it have assigned to it very
different dates, from the 1st of October, 583 B.C.,
by Scaliger, to the 3rd of February, 626 B.C.,
by Volnay. Professor Airy, by proceeding as
indicated above, and taking advantage of the
most recent data respecting the lunar
movements, has decided that this eclipse occurred on
the 28th of May, 584 B.C.

Between the earth and the moon there exists
one grand difference. The earth has an
atmosphere; the moon has none. She has no
clouds, snows, nor dews—contrary to the
theories of the elder astronomers. Kepler,
and Galileo, held the moon to be encompassed
with a heavy and elastic atmosphere: alleging,
among other proofs, that the moon sometimes
disappears in a clear sky, so as not to be
discoverable by the best glasses (of that day):
little stars of the fifth and sixth magnitude
remaining visible all the time.

Kepler says that he has observed this
phenomenon twice—once in 1580, and once in 1583.
Hevelius did the same in 1620. Ricciolus and
other Jesuits, at Bologna, and many people
throughout Holland, observed the like on the
14th of April, 1642. And yet at Venice and
Vienna the moon remained, all the while,
conspicuous. On December 23, 1703, there was
another total obscuration of the moon, which
must not be confounded with an eclipse. At
Aries, in France, she first appeared of a yellowish
brown; at Avignon, ruddy and transparent, as
if the sun were shining through her. At
Marseilles, one part was reddish, the other very
dusky; "and at length, although in a clear
sky, she wholly disappeared." Here it is