ipses are
not to be looked for save at two special epochs, which last about a
month each, and which are separated from one another and from the
eclipse seasons of the previous and of the following years by intervals
of about six months, within a few days more or less. Such, however, is
the case. A little thought will soon make it clear why such should be
the case. We have already seen that the Moon's orbit, like that of every
other planetary member of the Solar System, has two crossing places with
respect to the ecliptic which are called "Nodes." We know also that the
apparent motion of the Sun causes that body to traverse the whole of the
ecliptic in the course of the year. The conjoint result of all this is
that the Moon passes through a Node twice in every lunar month of 27
days, and the Sun passes (apparently) through a Node twice in every
year. The first ultimate result of these facts is that eclipses can only
take place at or near the nodal passages of the Moon and the Sun, and
that as the Sun's nodal passages are separated by six months in every
case the average interval between each set of eclipses, if there is more
than one, must in all cases be six months, more or less by a few days,
dependent upon the latitude and longitude of the Moon at or about the
time of its Conjunction or Opposition under the circumstances already
detailed. If the logic of this commends itself to the reader's mind, he
will see at once why eclipses or groups of eclipses must be separated by
intervals of about half an ordinary year. Hence it comes about that,
taking one year with another, it may be said that we shall always have a
couple of principal eclipses with an interval of half a year (say 183
days) between each; and that on either side of these dominant eclipses
there will, or may be, a fortnight before or a fortnight after, two
other pairs of eclipses with, in occasional years, one extra thrown in.
It is in this way that we obtain what it has already been said
dogmatically that we do obtain; namely, always in one year two eclipses,
which must be both of the Sun, or any number of eclipses up to seven,
which number will be unequally allotted to the Sun or to the Moon
according to circumstances.

Though it is roughly correct to say that the two eclipse seasons of
every year run to about a month each, in length, yet it may be desirable
to be a little more precise, and to say that the limits of time for
solar eclipses cover 36 days (na