length, or nearly twice as far as the distance of the moon from the earth! Then spots were seen of such a depth that when they reached the sun's edge they made a notch on the rim. It was evident they were not volcanoes spouting forth solid matter to immense heights and blackening with solar smoke the photosphere, as Schroeter called the envelope of light which clothed the sun. They were not dark bodies like planets circling round this fiery ball. Nor were they masses of black scum floating on an ocean of brightness. In 1779 Herschel saw a great spot which appeared to be divided into two parts. One of them was more than thirty-one thousand miles in length, the other was about twenty thousand, and a ridge of shining light separated the one from the other. Four years later he observed another, "a fine large spot," and followed it to the edge of the sun. He came to the conclusion that he was looking into a vast pit, with "very broad, shelving sides," on to "the real solid body of the sun itself." Eight years after, in 1791, he came to the same conclusion regarding another large spot: it was a pit below the level of the bright surface; round the dark part it had a broad margin less bright than the surface, and also lower down. Accompanying the spots were the faculæ, as Hevelius called "the ridges of elevation above the rough surface" of the sun. "About all the spots the shining matter seemed to have been disturbed; and was uneven, lumpy, and zigzagged in an irregular manner." These waves or ridges of brightness are of immense extent, but Herschel objected to call them torches, as "they appeared like the shrivelled elevations on a dried apple, extended in length, and most of them
