The elements of astronomy; a textbook . tru-ment, and the best atmospheric conditions, the surface is seento be made up, as shown in Fig. 46, of a comparatively darkishbackground, sprinkled over with grains or nodules as Her-schel calls them, of something much more brilliant, — likesnow-flakes on gray cloth, according to Langley. These nod-ules or rice grains are from 400 to 600 miles across, and inthe finest seeing, themselves break up into more minute gran-ules. For the most part, the nodules are about as broad asthey are long, though of irregular form; but here and there,especially in the n
The elements of astronomy; a textbook . tru-ment, and the best atmospheric conditions, the surface is seento be made up, as shown in Fig. 46, of a comparatively darkishbackground, sprinkled over with grains or nodules as Her-schel calls them, of something much more brilliant, — likesnow-flakes on gray cloth, according to Langley. These nod-ules or rice grains are from 400 to 600 miles across, and inthe finest seeing, themselves break up into more minute gran-ules. For the most part, the nodules are about as broad asthey are long, though of irregular form; but here and there,especially in the neighborhood of the spots, they are drawnout into long streaks, known as filaments, willow leaves,or thatch straws. Certain bright streaks called faculce are also usually visi-ble here and there upon the suns surface, and though not veryobvious near the centre of the disc, they become conspicuous § 184] SUN SPOTS. 123 near the limb/ especially in the neighborhood of the probably they are of the same material as the rest of. Fig. 46.—The Great Sun Spot of September, 1870, and the Structure of the a Drawing by Professor Langley. From the New Astronomy, by permission ofthe Publishers. the photosphere, but elevated above the general level, and in-tensified in brightness. 124 SUN SPOTS. [§184 Fig. 47 shows faculse around a spot near the suns photosphere is probably a sheet of clouds floating in aless luminous atmosphere, just as a cloud formed by the con-densation of water-vapor floats in the air. It is intenselybrilliant, for the same reason that the mantle of a Wels-bach burner outshines the gas-flame which heats it: the radiat-ing power of the solid and liquid particles which compose theclouds is extremely high.
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