rsed nearly a full quadrant, its
distance from its primary first increasing, till in 1831 the stars were
nearly 7-1/2 seconds apart, and thence slowly diminishing, so that at
present the stars are less than 5 seconds apart. The period usually
assigned to the revolution of this binary system is 117 years, and the
period of peri-astral passage is said to be 1779. It appears to me,
however, that the period should be about 108 years, the epoch of last
peri-astral passage 1777 and of next peri-astral passage, therefore,
1885. The angular motion of the secondary round the primary is now
rapidly increasing, and the distance between the components is rapidly
diminishing, so that in a few years a powerful telescope will be
required to separate the pair.

Not far from [xi] is [pi] Bootis, represented in Plate 5 as a somewhat
closer double, but in reality--now at any rate--a slightly wider pair,
since the distance between the components of [xi] has greatly diminished
of late. Both the components of [pi] are white, and their magnitudes are
3-1/2 and 6.

We shall next turn to an exceedingly beautiful and delicate object, the
double star [epsilon] Bootis, known also as Mirac and, on account of its
extreme beauty, called Pulcherrima by Admiral Smyth. The components of
this beautiful double are of the third and seventh magnitude, the
primary orange, the secondary sea-green. The distance separating the
components is about 3 seconds, perhaps more; it appears to have been
slowly increasing during the past ten or twelve years. Smyth assigns to
this system a period of revolution of 980 years, but there can be little
doubt that the true period is largely in excess of this estimate.
Observers in southern latitudes consider that the colours of the
components are yellow and blue, not orange and green as most of our
northern observers have estimated them.

A little beyond the lower left-hand corner of the map is the star
[delta] Serpentis, in the position shown in the Frontispiece, Map 3.
This is the star which at the hour and season depicted in Map 2 formed
the uppermost of a vertical row of stars, which has now assumed an
almost horizontal position. The components of [delta] Serpentis are
about 3-1/2 seconds apart, their magnitudes 3 and 5, both white.

The stars [theta]^{1} and [theta]^{2} Serpentis form a wide double, the
distance between the components being 21-1/2 seconds. They are nearly
equal in magnitude, the primary being 4-1/2, th