division of the galaxy is shewn in the following section, in which S is the position of the sun. The
Milky Way, when carefully examined, exhibits a mottled appearance, shewing an unequal distribution of stars. Some spots appear absolutely black, and one very marked is, from this circumstance, called the coal-sack; some look like holes or rather prolonged funnels, projecting beyond the general limits of the stratum. An idea may be formed of the crowding of the stars in the Milky Way from the fact, that in many places upwards of a thousand stars have been counted in a space which the disc of the moon would cover. Probably the whole number amounts to more than twenty millions.
But the Milky Way, with its outlying stars constituting our firmament, is only one of the many thousands of the stellar aggregations scattered throughout space. These are the nebulæ which, when resolved by adequate optical power, yield galaxies, wondrous from their dimensions and the strangeness of their forms. There are some nebulous masses quite visible to the naked eye. The most remarkable of these are the clouds of Magellan in the southern hemisphere. They are very conspicuous, and occupy
