gain, it must be noted that, although the maps are necessarily
arranged in a certain order, there is in reality no first or last
in the series. The map numbered I. follows the map numbered XII.
in exactly the same manner that the latter follows the map numbered
XI. The maps form a circular series, in fact.

The only reason for numbering the maps as at present, is that the map
numbered I. Happens to exhibit the aspect of the sky at a convenient
hour on the night of January 1st. It will be found that the dates
follow on with intervals of seven or eight days right round the year,
the end of the year falling in the left-hand column of the table
under Map I., while the beginning of the year is in the right-hand
column of the same map.[*]

[Footnote *: It may be mentioned in passing, that the dates have
not been thrown in so as to fall regularly round the year, but
correspond with the variations due to the earth's variable motion
round the sun.]

It will be seen at once that a map can always be found corresponding
to a convenient hour on any night of the year. (In midsummer, on
a few of the dates mentioned under the maps, night has not begun
at the hour named.) On any date named under a map, the aspect of
the sky two hours later than that named is that represented in
the following map. Thus at eight o'clock in the evening of January
22d, the aspect of the stars is as shown in Map I. At ten o'clock
on the same night the aspect of the sky is that shown in Map II., as
a date under that map shows. Applying this rule to the few occasions
on which the hour named is not available for observation (five or
six in all out of ninety-six dates), the observer can manage as
well for those occasions as for any others.

Next, as to finding the north point, or any point of the compass
which will enable the observer to determine the rest. If he is
only familiar with the aspect of those seven bright stars of the
Great Bear which have been called the Dipper, Charles' Wain, (really
"The Churl's Wain,") the Butcher's Cleaver, and by other names,
he can always determine the north point by means of the two stars
called the Pointers, since these seven stars never set. In the
explanation of each map I have shown where the Great Bear is to
be looked for on each night, the observer being assumed to have
such a general knowledge of the direction of the compass-points,
as will suffice for the purpose of finding so marked a collection
of stars. Thus