THE SUN.

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we have just referred, indicated a revolution of the Sun , aboutan axis of its figure, in about 25| days. The spots were oftenseen to be more or less surrounded, or preceded iu their appear-ance, by irregular markings of special brightness, to whichthe name of faculce was given. It was, moreover, evident thatthey were in many cases darkest in their central portions, andthat those portions were depressed below the surroundingsurface, which was proved by the effect of the gradual fore-shortening produced by the Sun ’s rotation, as it carried them

Fig. VII.—The change in the appearance of a spot caused by theSun ’s rotation proves that its central part is depressed belowthe surrounding surface.

from the edge to the centre of its disc, and vice versa. Thiseffect is illustrated in Fig . VII.

One attempt, and only one of any importance, had been madeup to the time to which we refer, to fathom the mystery ofthese spots. It proved, however, to be very erroneous, althoughit originated with so great an astronomer as Sir William Herschel . He put forward the hypothesis, that the very darkcentral portions of the Sun -spots might be parts of a solidnucleus existing within the fiery envelope which dazzles oursight, and that this nucleus appeared to be intensely black by