little erratic that they may be looked upon as members of the solar household. We have then

Eight large Planets, as follow, in the order of distance from the sun : 1. Mercury; 2. Venus; 3. EARTH; 4. Mars; 5. Jupiter; 6. Saturn; 7. Uranus; 8. Neptune.

One hundred and six small Planets revolving round the sun, between the orbits of Mars and Jupiter.

Meteoric bodies, which at times approach near the earth's orbit, and occasionally reach the earth's surface.

Comets.

The Zodiacal Light.-A ring of apparently nebulous matter, the exact nature and position of which in the system are not yet determined.

Let us next inquire into the various distances of the planets from the sun, bearing in mind, that as the orbits are elliptical, the planets are sometimes nearer to the sun than at other times. The average or mean distances are as follow; the sizes and times of revolution are also given :

Such, then, is the sun and his system, taken as a whole-a point of view not to be passed over in any general description of the sun. We now pass on to the telescopic appearance of the great central luminary.

II. WHAT THE SUN IS LIKE.

Having now got an idea of the sun's place in the universe, and his size, mass, and density, compared with our own earth, we may begin to scrutinise him somewhat more closely. One of the first triumphs of the telescope was the discovery of spots in the sun-a discovery which sent a thrill through the world of schoolmen, for they imagined that the fundamental Aristotelian doctrine of the immutability and incorruptibility of the heavens was thereby contravened. It is doubtful whether this discovery is to be attributed to the great Galileo, or to Fabricius, or even to our own countryman Harriot; it is certain, however, that they observed sun-spots about the years 1610 and 1611. It is not surprising that the strangest explanations of these curious solar phenomena were hazarded in those early times with the imperfect instruments then

in use. It was at length, however, suspected by Galileo that they really belonged to the sun, and were not planets revolving

Fig. 3.-General Telescopic Appearance of the Sun, shewing spots and faculæ.

round him; and from their motions he at once inferred that the sun turned on his axis like our own earth-some 25 days or so being required for a complete rotation. It needed, however, a period of

Fig. 4-Position of the Sun's Axis, and apparent paths of the spots across the disc, as seen from the Earth at different times of the year. The arrows shew the direction in which the sun turns round.

150 years to make any great step in advance on the work done by Galileo and his contemporaries, and this step we owe to Dr Wilson of Glasgow, who in the year 1769 shewed it to be very probable

Fig. 5.-Sun-spots (the great sun-spot of 1865): 1. The spot entering the sun's disc, October 7 (foreshortened view). 2. October 10. 3. October 14, central view, shewing the formation of a bridge, and the nucleus. 4. October 16.

that the spots were really cavities in the sun's outer shining surface, which is called the photosphere. This proof was based upon the change of appearance which a spot undergoes when seen near the sun's edge, called in astronomical language the limb, and when seen near the centre of the sun's disc; for it will readily be perceived that, owing to the sun's rotation, a spot first appears at one side, then travels across the visible disc, and finally disappears at the other side. Now, when we observe a spot in the centre of the sun, what we generally see is this: in the centre of the spot, a more or less regular patch of blackness, called the umbra, or shade; and surrounding this, and separating the umbra from the photosphere, a half-tone, called the penumbra. Sometimes in the umbra we get a still darker shade, called the nucleus, and surrounding the penumbra are often masses brighter than the general surface of the photosphere, which are called facula (Latin, torches).

When, however, a spot is seen close to the border or limb of the sun, we only see the penumbra on the side farther from the centre. Now, it is only possible to explain these appearances by supposing the umbra of a spot to be nearer the sun's centre than the penumbra; and if our readers will take the trouble to look a common flower-pot or any similar object full in the face, and then look along the top of it sideways, first on one side of them, then on the other, they will see the force of this reasoning. The truth of Wilson's observations has been since abundantly confirmed by an examination of Mr De La Rue's solar photographs taken at Kew.

Spots are regions of incessant change; sometimes in a day we may observe changes taking place which must have resulted from movements of almost incredible velocity, and, indeed, very careful observations reveal changes of less magnitude from hour to hour; and when we recollect that spots 50,000 miles across are not uncommon, and that, with our most powerful telescopes, we can only see what is going on as if the sun were situated some 180,000 miles away, we at once recognise that changes, to be seen at all, must be of a stupendous magnitude, to judge by our planetary standard.

From the spots we next come to the general surface. In a good telescope, the faculæ, which, as we have already stated, often surround a spot, are seen to be irregularly distributed all over the sun, appearing most distinctly when near the limb. The whole solar surface, including the faculæ, but excluding, of course, the spots, appears to be coarsely mottled, and to be made up of bright roundish patches with soft edges, sprinkled, without any approach to regularity, on a less luminous background. These roundish patches, when they are observed near a spot and in the penumbra, are seen to be drawn out as if by currents (like our clouds sometimes); and one is driven to the conclusion that the photosphere of the sun is really of a cloudy nature.

In what has gone before, we have merely alluded to the sun as