We turn to [map No. 18], and, beginning at the western end of the constellation Aquarius, we find the variable T, which ranges between magnitudes seven and thirteen in a period of about two hundred and three days. Its near neighbor Σ 2729 is a very close double, beyond the separating power of our five-inch, the magnitudes being six and seven, distance 0.6", p. 176°. Σ 2745, also known as 12 Aquarii, is a good double for the three-inch. Its magnitudes are six and eight, distance 2.8", p. 190°. In ζ we discover a beauty. It is a slow binary of magnitudes four and four, distance 3.1", p. 321°. According to some observers both stars have a greenish tinge. The star 41 is a wider double, magnitudes six and eight, distance 5", p. 115°, colors yellow and blue. The uncommon stellar contrast of white with light garnet is exhibited by τ, magnitudes six and nine, distance 27", p. 115°. Yellow and blue occur again conspicuously in ψ, magnitudes four and a half and eight and a half, distance 50", p. 310°. Rose and emerald have been recorded as the colors exhibited in Σ 2998, whose magnitudes are five and seven, distance 1.3", p. 346°.
The variables S and R are both red. The former ranges between magnitudes eight and twelve, period two hundred and eighty days, and the latter between magnitudes six and eleven, period about three hundred and ninety days.
The nebula 4628 is Rosse's "Saturn nebula," so called because with his great telescope it presented the appearance of a nebulous model of the planet Saturn. With our five-inch we see it simply as a planetary nebula. We may also glance at another nebula, 4678, which appears circular and is pinned with a little star at the edge.
The small constellation Equuleus contains a surprisingly large number of interesting objects. Σ 2735 is a rather close double, magnitudes six and eight, distance 1.8", p. 287°. Σ 2737 (the first star to the left of Σ 2735, the name having accidentally been omitted from the [map]) is a beautiful triple, although the two closest stars, of magnitudes six and seven, can not be separated by our instruments. Their distance in 1886 was 0.78", p. 286°, and they had then been closing rapidly since 1884, when the distance was 1.26". The third star, of magnitude eight, is distant 11", p. 75°. Σ 2744 consists of two stars, magnitudes six and seven, distance 1.4", p. 1.67°. It is probably a binary. Σ 2742 is wider double, magnitudes both six, distance 2.6", p. 225°. Another triple, one of whose components is beyond our reach, is γ. Here the magnitudes are fifth, twelfth, and sixth, distances 2", p. 274° and 366". It would also be useless for us to try to separate δ, but it is interesting to remember that this is one of the closest of known double stars, the magnitudes being fourth and fifth, distance 0.4", p. 198°. These data are from Hall's measurements in 1887. The star is, no doubt, a binary. With the five-inch we may detect one and perhaps two of the companion stars in the quadruple β. The magnitudes are five, ten, and two eleven, distances 67", p. 309°; 86", p. 276°; and 6.5", p. 15°. The close pair is comprised in the tenth-magnitude star.
[Map No. 19] introduces us to the constellation Pegasus, which is comparatively barren to the naked eye, and by no means rich in telescopic phenomena. The star ε, of magnitude two and a half, has a blue companion of the eighth magnitude, distance 138", p. 324°; colors yellow and violet. A curious experiment that may be tried with this star is described by Webb, who ascribes the discovery of the phenomenon to Sir John Herschel. When near the meridian the small star in ε appears, in the telescope, underneath the large one. If now the tube of the telescope be slightly swung from side to side the small star will appear to describe a pendulumlike movement with respect to the large one. The explanation suggested is that the comparative faintness of the small star causes its light to affect the retina of the eye less quickly than does that of its brighter companion, and, in consequence, the reversal of its apparent motion with the swinging of the telescope is not perceived so soon.
The third-magnitude star η has a companion of magnitude ten and a half, distance 90", p. 340°. The star β, of the second magnitude, and reddish, is variable to the extent of half a magnitude in an irregular period, and γ, of magnitude two and a half, has an eleventh-magnitude companion, distance 162", p. 285°.
