Note 1 — III THE EVENING SKY AT THE AUTUMNAL EQUINOX

The reader who is curious concerning such matters is advised to consult a paper by Dr. Louis Bell on “Star Colors,” in the Astrophysical Journal (vol. xxi, No. 3, April, 1910). Dr. Bell’s experiments with artificial stars seem to show that physiological effects play a great part in producing the pronounced colors of the small stars in many telescopic doubles. The paper is very interesting, especially in its description of a startling imitation of the singular cluster, Kappa (κ) Crucis, which Sir John Herschel described as resembling a gorgeous piece of colored jewelry. But, whatever part physiological optics may play in the phenomena of colored doubles, it is certain that many single stars, including some of great magnitude, possess distinctive tints. Compare, for instance, Castor and Pollux or Rigel and Betelgeuse. Aldebaran and Betelgeuse are both reddish, yet the color tones that they exhibit are clearly different.