part at least of the shelving sides to be elevated above the surface of the Sun; and observed that, contrary to what usually happens, the margin of that side of the spot which was farthest from the limb was the broadest.' It will be noticed that in the picture of the Sun presented in Plate I., Mr. Browning delineates in the case of one spot of the group a precisely analogous

appearance.

Sir William Herschel's explanation of these peculiar appearances need not be quoted, as it has been disposed of by recent researches.

In the year 1791,' he proceeds, I examined a large spot in the Sun, and found it evidently depressed below the level of the surface; about the third part was a broad margin or plane of considerable extent, less bright than the Sun, and also lower than its surface. This plane seemed to rise, with shelving sides, up to the place where it joined the level of the surface.'

How very ill,' proceeds Herschel, would this

* Herschel reasons that there could have been no deception in this appearance, because the Sun looked convex, whereas he had noticed that on those occasions when the Moon's mountains and valleys were apparently reversed, the Moon herself always looked concave, the illusion disappearing when the mind was directed to the fact of the Moon being in truth convex. It may be questioned, however, whether this reasoning can fairly be applied to a self-luminous body. The peculiarity affecting the apparent concavity or convexity of the lunar mountains or craters, depends entirely on the ideas present in the mind at the moment of observation, respecting the direction in which the source of illumination lies-precisely as in the analogous experiment with a seal or coin, discussed in Brewster's Natural Magic. Such considerations cannot affect our views respecting a self-luminous body.

N

observation agree with the ideas of solid bodies bobbing up and down in a fiery liquid-with the smoke of volcanoes, or scum upon an ocean; and how easily is it explained upon our foregoing theory. The removal of the shining atmosphere, which permits us to see the Sun, must naturally be attended with a gradual diminution on its borders; an instance of a similar kind we have daily before us, when through the opening of a cloud we see the sky, which generally is attended by a surrounding haziness of some short extent, and seldom transits from a perfect clearness to its greatest obscurity.'

On August 26, 1792, Herschel examined the Sun with several powers, from 90 to 500. It appears evidently' he remarks, that the black spots are the opaque ground or body of the Sun; and that the luminous part is an atmosphere, which, being interrupted or broken, gives us a transient glimpse of the Sun itself.' He presently suggests that possibly even where there are no spots, the real surface of the Sun may now and then be perceived as we see the shape of the wick of a candle through its flame, or the contents of a furnace in the midst of the brightest glare of it; but this, I should suppose, will only happen where the lucid matter of the Sun is not very accumulated.'

A few days later he studied some well-marked faculæ. In the neighbourhood of a dark spot pretty near the edge, 'I saw,' he says, a great number of elevated bright places, making various figures. I shall call them faculæ, with Hevelius; but without assign

ing to this term any other meaning than what it will hereafter appear ought to be given to it. I see these faculæ extended on the preceding side, over about one-sixth part of the Sun; but so far from resembling torches, they appear to me like the shrivelled elevations upon a dried apple, extended in length; and most of them are joined together, making waves, or waving lines. By some good views in the afternoon, I find

The Sun's corrugated surface.-Secchi.

that the rest of the surface of the Sun does not contain any faculæ, except a few on the following and equatorial part of the Sun. Towards the north and south I see no faculæ; there is all over the Sun a great unevenness in the surface, which has the appearance of a mixture of small points of an unequal light; but

they are evidently an unevenness or roughness of high and low parts.'

The accompanying views (figs. 44 and 45) of portions of the Sun's surface, as delineated by Secchi with the fine telescope of the Roman observatory, correspond exactly with this description. Note also the drawing by Chacornac (fig. 55) farther on.

After a week's observations of the faculæ, Herschel thus reasons about them :-The faculæ being eleva

The Sun's suriace, showing lacula.-Secchi.

tions, very satisfactorily explains the reason why they disappear towards the middle of the Sun, and reappear on the other margin; for, about the place where we lose them they begin to be edgeways to our view; and if between the faculæ should lie dark spots, they will most frequently break out in the middle of the Sun,

because they are no longer covered by the side views of these faculæ,"*

On September 22, 1792, Herschel observed few faculæ on the Sun and few spots, but the whole disc very much marked with roughness, like an orange, and some of the lowest parts of the inequalities blackish. On the following day he thus associates this roughness with the faculæ :- The faculæ are ridges of elevation above the rough surface.'t

On February 23, 1794, Herschel noticed an appearance which is very well illustrated in Mr. Browning's drawing of the Sun, Plate I. One of the black spots on the preceding margin, which was greatly below the margin of the Sun, had, next to it, a protuberant lump of shining matter, a little brighter than the rest of the Sun. About all the spots,' he adds, the shining matter seems to have been disturbed; and is even lumpy and zig-zagged in an irregular manner. I call the spots black, not that they are entirely so, but merely to distinguish them; for there is not one of them to-day which is not partly or entirely covered with whitish and unequally bright nebulosity or cloudiness. This in many of them comes

* Perhaps the most convincing proof we have of the fact that faculæ are elevations, is that supplied by Mr. Dawes, who actually saw a facula projecting from the edge of the Sun's disc.

The observation next following the above in Herschel's paper (Phil. Trans. vol. lxxxv.) is worth citing, though the fact involved is now well-known to all observers of the Sun. It runs thus :-'Feb. 23, 1794. By an experiment I have just now tried, I find it confirmed that the Sun cannot be so distinctly viewed with a small aperture and faint darkening glasses as with a large aperture and stronger ones; this latter is the method I always use.'