HERSCHEL'S THEORY OF THE SPOTS 163 



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 photo- 

 sphere, 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 bright- 

 ness. 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 faculce, 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 



