2. Oct.

1. The spot entering the Sun's disk Oct. 7th (foreshortened view). 10th. 3. Oct. 14th; central view, showing the formation of a bridge, and the nucleus. 4. Oct. 16th.

often surround a spot, and hence appear the more conspicuous; such a ridge is shown in Fig. 1, Plate IV.; but sometimes there appears a very broad white platform round the spot, and from this the white crumpled ridges pass in various directions.

114. So much for the more salient phenomena of the Sun's surface, which we can study with our telescopes. There is much more, however, to be inquired into ; and here we may remark that the Sun himself has bestowed a great boon upon observational Astronomy; and, whether brightly shining or hid in dim eclipse, now tells his own story, and prints his image in all parts of the world on a retina which never forgets, and is withal so sensitive as to receive, in a small fraction of a second, impressions of more exact detail than could be made out by hours of scrutiny with a powerful telescope.

F

115. We may begin by saying, that the whole surface of the Sun, except those portions occupied by the spots, is more or less finely mottled; as, indeed, may be seen with no very large amount of optical power. The general arrangement of this mottling comes out very plainly in some photographs of the Sun lately taken by Dr. Janssen at the Meudon Observatory near Paris. They show blurred patches circumscribed by what seem like currents of fine, distinct granulation. This curious appearance is known as the "photospheric network." The luminous masses between the dusky marblings present an irregularly rounded form : they have been variously called "nodules," "floccules," "rice grains," "granules or granulations," and

so on.

FIG. 11.-Part of a Sun-spot. "Willow-leaves" detaching themselves from the penumbra. A very faint one at F.

116. The word "willow-leaf" very well paints the

appearance of the minute details sometimes observed in the penumbra of spots, which occasionally are made up apparently of elongated masses of unequal brightness, so arranged that for the most part they point like so many arrows to the centre of the nucleus, giving to the penumbra a radiated appearance. At other times and occasionally in the same spot, the jagged edge of the penumbra projecting over the nucleus has caused the interior edge of the penumbra to be likened to coarse thatching with

straw.

117. There are darker or shaded portions between the granules, often pretty thickly covered with dark dots, like stippling with a soft lead-pencil; these are what were called "pores,” or “incipient openings,” by Sir William Herschel. They are sometimes almost black, and are like excessively small spots.

118. When the Sun is totally eclipsed, that is, as will be explained by and by, when the Moon comes exactly between the Earth and the Sun,-other appearances are unfolded to us, which the extreme brightness of the Sun prevents our observing under ordinary circumstances: the Sun's atmosphere is seen to contain red masses of fantastic shapes, some of them quite disconnected from the Sun; to these the names of "red-flames" and "prominences" have been given. These are the higher waves of the more vivid portions of a solar envelope, from 5,000 to 10,000 miles in height, called the CHROMOSPHERE, which overlies the photosphere, and is composed chiefly of hydrogen, and an unknown gas named "helium." Outside the chromosphere lies the coronal atmosphere of the Sun, extending to an undetermined, and perhaps variable distance. On these appearances we shall say a word or two further on when we come to deal with Eclipses.

LESSON IX-Explanation of the Appearances on the Sun's Surface. The Sun's Light and Heat. Sun-force. The Past and Future of the Sun.

119. We are now familiar with the appearances presented to us on the Sun's surface in a powerful telescope. Let us see if we can account for them. As the spots break out and close up with great rapidity, as changes both on a large and small scale are always going on on the surface, we can only infer that the photosphere of the Sun, and therefore of the stars, is of a cloudy nature; but while our clouds are made up of particles of water, the clouds on the Sun must be composed of particles of various metals and other substances in a state of intense heat-how hot we shall see by and by. The photosphere is surrounded by an atmosphere composed of the vapours of the bodies which are incandescent in the photosphere. It seems also, that not only is the visible surface of the Sun entirely of a cloudy nature, but that the atmosphere is a highly absorptive one. Moreover its absorption chiefly affects the blue, or more refrangible end of the spectrum, so that, if it were removed, sunlight would be very much bluer than it actually is.

119 a. Faculæ reach high up into this atmosphere, and consequently escape some of its absorption. This accounts for their brilliancy, and also for their increased conspicuousness (as shown in Plate IV.) near the edge of the Sun, where they are thrown into relief by a greater depth of atmosphere. Faculæ really consist of the bright granules, or "domes" of the Sun's mottled surface, heaped up together, or arranged in certain directions. Though by no means confined to the vicinity of spots, they are closely associated with them. Their development, however, is always subsequent to that of spots, and they appear predominantly on their left-hand borders. They exist on a