50 SCENERY OF THE HEAVENS. 



the circle itself, or within several degrees of it. They are thus confined to two belts of the 

 solar surface, parallel to its equator, corresponding in some degree to the two temperate 

 zones of the earth. 



Intervals of some length have occurred, during which the disk of the sun has been 

 comparatively pure. This was the case from the year 1650 to 1670; and in 1724 the 

 surface appeared unblemished. But from 1611 to 1629, according to Scheiner, it was 

 never free from tarnish, except for a few days in December 1624. At a more recent date, 

 scarcely a year has passed without spots being seen, many of which have been of great 

 magnitude. It is supposed by Schwabe, whose observations have been continued without 

 intermission for more than thirty years, that the extent of the solar surface obscured by 

 spots increases and decreases periodically, the length of the period being eleven years and 

 forty days. This remarkable conclusion has attracted great attention ; and upon the 

 suggestion of Sir John Herschel, a photo-heliographic apparatus has lately been established 

 at Kew, for the purpose of depicting the actual state of the solar disk from time to time. 

 It has been thought, that spots of vast extent, or unusually numerous, may have the effect 

 of depressing the terrestrial temperature, and thus affect the fertility of the seasons. But 

 so far from such an inference being in harmony with observed facts, some of our warmest 

 seasons have coincided with an accumulation of spots on the sun. 



Besides the dark spots, or maculce, as they are called, the telescope has disclosed other 

 interesting appearances on the sun's disk. There are parts brighter than the rest of the 

 surface luminous aggregations to which the term faculce (little torches) has been applied. 

 They occasionally exhibit a round form, but have generally an extended, ridge-like shape. 

 Though commonly seen in the immediate neighbourhood of spots, they sometimes appear 

 alone, in which case they are almost always the precursors of spots, which become visible 

 on the following day. Messier was frequently enabled by these brilliant indications to 

 predict the appearance of spots twenty-four hours before they actually presented themselves 

 on the disk. While the faculse are confined to the " royal zone," or region of the spots, the 

 remainder of the solar surface is diversified with minute luminous specks and streaks, of 

 varying brightness. These are bordered by more obscure parts, in which a multitude of 

 small pores are observed, as black as the nuclei of the spots. The resulting mottled and 

 corrugated aspect of the sun, Herschel compared to the roughness of an orange. 



Conjecture has been busy respecting the nature of these appearances, their cause, and 

 probable indications respecting the physical constitution of the body to which they belong. 

 The early observers, indulging the vagaries of imagination, supposed the spots to be the 

 fuel of the solar furnace, or ashes floating on the surface of an abyss of combustion, or the 

 smoke of volcanic explosions. But the views first broached by Dr Wilson of Glasgow, 

 founded upon a minute examination of their peculiarities, substantially adopted and 

 amplified by Herschel, now generally obtain with 'astronomers. It seems scarcely to admit 

 of doubt, that the sun is a solid body, surrounded by two envelopes, suspended in a 

 transparent atmosphere ; the upper one luminous, forming the visible surface ; the lower 

 obscure, a layer of dense clouds, highly reflective, throwing back the light of the upper 

 regions. In these strata, temporary openings or rents are supposed to be made by currents 

 operating from below, analogous to the hurricanes and tornadoes of our tropical districts. 

 The altered appearance of the spots, as they are carried round by the solar rotation, 

 strikingly confirm the fact that they are excavations ; for after passing the centre of the 

 disk, the penumbra is impaired on the side nearest to it, and gradually disappears ; then 

 the nucleus is nipped on the same side, till it vanishes ; and then, finally, the penumbra 

 on the opposite side begins to contract, narrows to a line, and is carried out of sight. 

 These variations are exactly those which depressions will present in the course of rotation. 

 Adopting this view, the nucleus of a spot is the exposed dense body or solid substance of 



