[Page 210] Number.

We find about five thousand stars visible to the naked eye in the whole heavens, both north and south.  Of these twenty are of the first magnitude, sixty-five of the second, two hundred of the third, four hundred of the fourth, eleven hundred of the fifth, and three thousand two hundred of the sixth.  We think we can easily number the stars; but train a six-inch telescope on a little section of the Twins, where six faint stars are visible, and over three thousand luminous points appear.  The seventh magnitude has 13,000 stars; the eighth, 40,000; the ninth, 142,000.  There are 18,000,000 stars in the zone called the Milky Way.  When our eyes are not sensitive enough to be affected by the light of far-off stars the tastimetre feels their heat, and tells us the word of their Maker is true—­“they are innumerable."[*]

[Footnote *:  Telescopic Work.—­Look at the Hyades and Pleiades in Taurus.  Notice the different colors of stars in them both.  Find the cluster Praesepe in Fig. 70, just a trifle above a point midway between Procyon and Regulus.  It is equally distant from Procyon and a point a little below Pollux.  Sweep along the Milky Way almost anywhere, and observe the distribution of stars; in some places perfect crowds, in others more sparsely scattered.  Find with the naked eye the rich cluster in Perseus.  Draw a line from Algol to a of Perseus (Fig. 67); turn at right angles to the right, at a distance of once and four-tenths the first line a brightness will be seen.  The telescope reveals a gorgeous cluster.]

Double and Multiple Stars.

If we look up during the summer months nearly overhead at the star e Lyra, east of Vega (Fig. 72), we shall see with the naked eye that the star appears a little [Page 211] elongated.  Turn your opera-glass upon it, and two stars appear.  Turn a larger telescope on this double star, and each of the components separate into two.  It is a double double star.  We know that if two stars are near in reality, and not simply apparently so by being in the same line of sight, they must revolve around a common centre of gravity, or rush to a common ruin.  Eagerly we watch to see if they revolve.  A few years suffice to show them in actual revolution.  Nay, the movement of revolution has been decided before the companion star was discovered.  Sirius has long been known to have a proper motion, such as it would have if another sun were revolving about it.  Even the direction of the unseen body could always be indicated.  In February, 1862, Alvan Clark, artist, poet, and maker of telescopes (which requires even greater genius than to be both poet and artist), discovered the companion of Sirius just in its predicted place.  As a matter of fact, one of Mr. Clark’s sons saw it first; but their fame is one.  The time of revolution of this pair is fifty years.  But one companion does not meet the conditions of the movements.  Here must also be one or more planets too small or dark to be seen.  The double star x in the Great Bear (see Fig. 70) makes a revolution in fifty-eight years.