1937, 1955, and 1973, affords an excellent instance of the northward
progression of eclipse tracks; and another series, with totality nearly
as great (1850, 1868, 1886, 1904, and 1922), is progressing slowly
southwards."

The word "Digit," formerly used in connection with eclipses, requires
some explanation. The origin of the word is obvious enough, coming as it
does from the Latin word _Digitus_, a finger. But as human beings have
only eight fingers and two thumbs it is by no means clear how the word
came to be used for twelfths of the disc of the Sun or Moon instead of
tenths. However, such was the case; and when a 16th-century astronomer
spoke of an eclipse of six digits, he meant that one-half of the
luminary in question, be it Sun or Moon, was covered. The earliest use
of the word "Digit" in this connection was to refer to the twelfth part
of the visible _surface_ of the Sun or Moon; but before the word went
out of use, it came to be applied to twelfths of the visible _diameter_
of the disc of the Sun or Moon, which was much more convenient. However,
the word is now almost obsolete in both senses, and partial eclipses,
alike of the Sun and of the Moon, are defined in decimal parts of the
diameter of the luminary--tenths or hundredths according to the amount of
precision which is aimed at. Where an eclipse of the Moon is described
as being of more than 12 Digits or more than 1.0 (= 1 diameter) it is to
be understood that the eclipse will be (or was) not only total, but that
the Moon will be (or was) immersed in the Earth's shadow with a more or
less considerable extent of shadow encompassing it.

There are some further matters which require to be mentioned connected
with the periodicity of eclipses. To use a phrase which is often
employed, there is such a thing as an "Eclipse Season," and what this is
can only be adequately comprehended by looking through a catalogue of
eclipses for a number of years arranged in a tabular form, and by
collating the months or groups of months in which batches of eclipses
occur. This is not an obvious matter to the casual purchaser of an
almanac, who, feeling just a slight interest in the eclipses of a coming
new year, dips into his new purchase to see what those eclipses will be.
A haphazard glance at the almanacs of even two or three successive years
will probably fail to bring home to him the idea that each year has its
own eclipse season in which eclipses may occur, and that ecl