[Illustration:  Fig. 75.—­Aspects and Revolution of Double Stars.]

The meaning of these double stars is that two or more suns revolve about their centre of gravity, as the moon and earth about their centre.  If they have planets, as doubtless they have, the movement is no more complicated than the planets we call satellites of Saturn revolving about their central body, and also about the sun.  Kindle Saturn and Jupiter to a blaze, or let out their possible light, and our system would appear a triple star in the distance.  Doubtless, in the far past, before these giant planets were cooled, it so appeared.

We find some stars double, others triple, quadruple, octuple, and multiple.  It is an extension of the same principles that govern our system.  Some of these suns are so far asunder that they can swing their Neptunes between them, with less perturbation than Uranus and Neptune have in ours.  Light all our planets, and there would be a multiple star with more or less suns seen, [Page 214] according to the power of the instrument.  Perhaps the octuple star s in Orion differs in no respect from our system, except in the size and distance of its separate bodies, and less cooling, either from being younger, or from the larger bodies cooling more slowly.  Suns are of all ages.  Infinite variety fills the sky.  It is as preposterous to expect that every system or world should have analogous circumstances to ours at the present time, as to insist that every member of a family should be of the same age, and in the same state of development.  There are worlds that have not yet reached the conditions of habitability by men, and worlds that have passed these conditions long since.  Let them go.  There are enough left, and an infinite number in the course of preparation.  Some are fine and lasting enough to be eternal mansions.

Colored Stars.

In the cloudy morning we get only red light, but the sun is white.  So Aldebaran and Betelguese may be girt by vapors, that only the strong red rays can pass.  Again, an iron moderately heated gives out dull red light; becoming hotter, it emits white light.  Sirius, Regulus, Vega, and Spica may be white from greater intensity of vibration.  Procyon, Capella, and Polaris are yellow from less intensity of vibration.  Again, burn salt in a white flame, and it turns to yellow; mix alcohol and boracic acid, ignite them, and a beautiful green flame results; alcohol and nitrate of strontia give red flame; alcohol and nitrate of barytes give yellow flame.  So the composition of a sun, or the special development of anyone substance thereof at any time, may determine the color of a star.

[Page 215] The special glory of color in the stars is seen in the marked contrasts presented in the double and multiple stars.  The larger star is usually white, still in the intensity of heat and vibration; the others, smaller, are somewhat cooled off, and hence present colors lower down the scale of vibration, as green, yellow, orange, and even red.