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the sixth magnitude, which included the faintest stars that the best eye could see under a clear sky.

Modern astronomers carry this system down to the telescopic stars. Those which are one degree fainter than the smallest visible to the naked eye are called of the seventh magnitude; the next in brightness are of the eighth, and so on. The faintest that can be seen or photographed with the largest telescopes are probably of the fifteenth, sixteenth, or seventeenth magnitude.

The reader will of course understand that the magnitude of a star does not express its real brightness, because a shining body looks brighter the nearer it is to us. No matter how bright a star may be, if it were removed far enough away it would grow so faint as to be invisible. The smallest star in the heavens if brought near enough to us would shine as of the first magnitude.

It was formerly believed that the actual brightness of the different stars was nearly the same, and that some looked brighter than others only because they were nearer to us. But the case is now known to be different. Estimates of the distance of the stars show that among the nearest to us are many quite invisible to the naked eye, while some of the first magnitude are so far away that their distance is immeasurable. The brightest ones probably emit hundreds of thousands of times as much light as the smallest ones.

The whole number of stars in the heavens which can be seen by the ordinary eye is between five and six thou-