Page:Popular Science Monthly Volume 47.djvu/531

Rh 75°. Σ 2744 consists of two stars, magnitudes six and seven, distance 1·6″, p. 171°. It is probably a binary. Σ 2742 is a 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 fifth, tenth, and two eleventh, 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, distant 162″, p. 285°.

Our interest is revived on turning, with the guidance of map No. 20, from the comparative poverty of Pegasus to the spacious constellation Cetus. The first double star that we meet in this constellation is 26, whose components are of magnitudes six and nine, distance 16·4″, p. 252°; colors, topaz and lilac. Not far away is the closer double 42, composed of a sixth and a seventh magnitude star, distance 1·25″, p. 350°. The four-inch is capable of splitting this star, but we shall do better to use the five-inch. In passing we may glance at the tenth-magnitude companion to η. distant 225″, p. 304°. Another wide pair is found in, magnitudes third and ninth, distance 185″, p. 40°.