CHAPTER X.
SUN-SPOTS.
Grave Doubts.
Herbert Spencer says: "At present none of the interpretations of the sun-spots can be regarded as established."
How numerous and how strange have been the theories promulgated as to the character of the manifestations called sun-spots. The dark spots in the sun have been supposed to be "solid bodies revolving very near its surface," "Smoke of volcanoes;" "Scum floating upon an ocean of fluid matter;" "Clouds;" "Opaque masses floating in the fluid matter of the sun, dipping down occasionally," "Fiery liquid surrounding the sun which, by its ebbing and flowing, the highest parts of it were occasionally uncovered, and appeared under the shape of dark spots, and by the return of the fiery liquid, they were again covered, and in a manner successively assumed different phases;" "Interruptions of continuity in the bright envelopes immediately surrounding the sun," "Cavities" etc.
Overestimate of the Degree of Spot-shadow.
Public sentiment in regard to the degree of darkness which is disclosed in sun-spots is exceedingly erroneous. It is believed that the spots are really dark. Zöllner, however, states that "The black umbra of a spot emits four thousand times as much light as that derived from an equal area of the moon." "The blackest part of the spot is intrinsically bright."