These spots may be seen with almost any telescope, the eye being protected by deeply colored glasses.

Until within one hundred years they were supposed to be islands of scoriae floating in the sea of molten matter.  But they were depressed below the surface, and showed a notch when on the edge.  Wilson originated and Herschel developed the theory that the sun’s real body was dark, cool, and habitable, and that the photosphere was a luminous stratum at a distance from the real body, with openings showing the dark spots below.  Such a sun would have cooled off in a week, but would previously have annihilated all life below.

The solar spots being most abundant on the two sides of the equator, indicates their cyclonic character; the centre of a cyclone is rarefied, and therefore colder, and cold on the sun is darkness.  M. Faye says:  “Like our cyclones, they are descending, as I have proved by a special study of these terrestrial phenomena.  They carry down into the depths of the solar mass the cooler materials of the upper layers, formed principally of hydrogen, and thus produce in their centre a decided extinction of light and heat as long as the gyratory movement continues.  Finally, the hydrogen set free at the base of the whirlpool becomes reheated at this [Page 92] great depth, and rises up tumultuously around the whirlpool, forming irregular jets, which appear above the chromosphere.  These jets constitute the protuberances.  The whirlpools of the sun, like those on the earth, are of all dimensions, from the scarcely visible pores to the enormous spots which we see from time to time.  They have, like those of the earth, a marked tendency, first to increase and then to break up, and thus form a row of spots extending along the same parallel.”

[Illustration:  Fig. 36.—­Solar spot, by Langley.]

A spot of 20,000 miles diameter is quite small; there was one 14,816 miles across, visible to the naked eye for a week in 1843.  This particular sun-spot somewhat [Page 93] helped the Millerites.  On the day of the eclipse, in 1858, a spot over 107,000 miles in extent was clearly seen.  In such vast tempests, if there were ships built as large as the whole earth, they would be tossed like autumn leaves in an ocean storm.

The revolution of the sun carries a spot across its face in about fourteen days.  After a lapse of as much more time, they often reappear on the other side, changed but recognizable.  They often break ont or disappear under the eye of the observer.  They divide like a piece of ice dropped on a frozen pond, the pieces sliding off in every direction, or combine like separate floes driven together into a pack.  Sometimes a spot will last for more than two hundred days, recognizable through six or eight revolutions.  Sometimes a spot will last only half an hour.