[Illustration: FIG. 10.--SEPT. 26, 1870.] Next we have six enlarged views of it on the 19th, 20th, 21st, 22d, 23d, and 26th. On the 19th it is seen very near the eastern limb, showing like a great hole in the sun, and foreshortened as it comes into view around the dark edge; for the edge of the sun is really darker than the central parts, as it is shown here, or as one may see even through a smoked glass by careful attention. On the 20th we have the edge still visible, but on the 21st the spot has advanced so far that the edge cannot be shown for want of room. We see distinctly the division of the spot into the outer shades which constitute the penumbra, and the inner darker ones which form the umbra and nucleus. We notice particularly in this enlarged view, by comparing the appearances on the 21st, 22d, and 23d, that the spot not only turns with the sun (as we have already learned), but moves and changes within itself in the most surprising way, like a terrestrial cloud, which not only revolves with the rest of the globe, but varies its shape from hour to hour. This is seen still more plainly when we compare the appearance on the 23d with that on the 26th, only three days later, where the process has begun by which the spot finally breaks up and forever disappears. On looking at all this, the tremendous scale on which the action occurs must be borne in mind. On the 21st, for instance, the umbra, or dark central hole, alone was large enough to let the whole globe of our own earth drop in without touching the sides! We shall have occasion to recur to this view of the 21st September again. [Illustration: FIG. 11.--NASMYTH’S WILLOW LEAVES. (FROM HERSCHEL’S “OUTLINES OF ASTRONOMY.”)] In looking at this spot and its striking changes, the reader must not omit to notice, also, a much less obvious feature,--the vaguely seen mottlings which show all over the sun’s surface, both quite away from the spots and also close to them, and which seem to merge into them. [Illustration: FIG. 12.--THE CACTUS TYPE. (FROM SECCHI’S “LE SOLEIL.”)]