Essays and addresses / by professors and lectures of the Owens College, Manchester.

Date:
1874
Catalogue details

Licence: Public Domain Mark

Credit: Essays and addresses / by professors and lectures of the Owens College, Manchester. Source: Wellcome Collection.

    98/584 page 77
    III.] SOLAR PHYSICS. 77 sun-spots was first observed by Wilson ; he saw that they behaved as if they were pits with sloping sides, and came to the conclusion that they were in reality caverns of this nature. Another reason in favour of these spots being hol¬ lows is derived from the fact that bright matter has been seen to sail across a spot leaving everything the same as before, just as a bird might fly across the mouth of a pit while it would be lost in a cloud. A third reason is derived from the spectroscopic obser¬ vations of Lockyer, who finds that the light which reaches us from the matter at the bottom of a spot is such as to denote the existence of a greater atmo¬ spheric pressure or denser state of things than at the surface of the sun. Now in the sun, just as in our own atmosphere, a great pressure corresponds to a great depth. All these facts go to show that sun- spots denote depressions in the cloudy surface of the sun. 2 2. Having thus described the large black patches or sun-spots, let us say a few words regarding certain peculiarly bright patches, called faculœ, which are generally seen to accompany spots. As we have three reasons for imagining sun-spots to be depressions, so we have at least two reasons for imagining faculae to consist of the luminous matter of the sun thrown up high into the solar atmosphere. One of these is derived from the fact that the faculae are generally behind the accompanying spot as regards the direction in which the sun is rotating. This can easily be explained on the supposition that the faculae represent matter which has been thrown up from a
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