CHAP. 58.—THE RISING AND SETTING OF THE STARS.
The whole of this system is based upon the observation of
three branches of the heavenly phænomena, the rising of the
constellations, their setting, and the regular recurrence of the
seasons. These risings and settings may be observed in two
different ways:—The stars are either concealed, and cease to
be seen at the rising of the sun, or else present themselves to
our view at his setting—this last being more generally known
by the name of "emersion" than of "rising," while their dis-
appearance is rather an "occultation" than a "setting."—
Considered, again, in another point of view, when upon certain days
they begin to appear or disappear, at the setting
or the rising of the sun, as the case may be, these are called
their morning or their evening settings or risings, according
as each of these phenomena takes place at day-break or twilight.
It requires an interval of three quarters of an hour at least before
the rising of the sun or after his setting, for the stars to
be visible to us. In addition to this, there are certain stars
which rise and set twice.1
All that we here state bears
reference, it must be remembered, to the fixed stars only.