occupied by our own moon. The largest of Jupiter's moons has a mass less than the 110,000th part of Jupiter's; our moon, on the contrary, is about equal to the eightieth part of the earth. As respects mass, our moon is in fact rather to be regarded as the fifth and smallest member of the inner family of planets, than as occupying a totally inferior position as a body of another order. The earth exceeds Mercury very much more, as well in mass as in volume, than Mercury exceeds the moon. Jupiter's moons, on the other hand, belong as distinctly to an inferior order, when compared with him or his fellow giants among the planets, as our earth when compared with the sun.

Now, our difficulties begin to diminish when we regard the moons of Jupiter as the abode of life, and Jupiter as the ruler of the system, subordinate of course to the sun. For we must remember that every one of Jupiter's moons is in reality a planet travelling round the sun. Each one

of them has its year, its day, and probably its seasons. For anything, indeed, that is known, the inhabitants of each may regard their little world as the centre of the universe; since to a creature placed on one of those moons all the circumstances would be presented which caused the ancients to regard our earth as the fixed centre of created things. Jupiter must appear to them as a gigantic moon; and he really is capable of compensating them to a noteworthy extent for the small amount of light supplied to them by the sun. Certainly this is the case with the nearest moon, since Jupiter must show a

disc exceeding our moon's more than fourteen hundred. times in apparent surface, and supplying more than fifteen hundred times as much light as our full moon. Even in the case of the outermost moon the apparent surface of Jupiter's disc must exceed that of our moon about sixty-five times, and supply about eight times as much light. It may be noticed that we have not reduced fourteen hundred or sixty-five to their twenty-fifth part, as might appear to be the proper course on account of the diminution of the sun's light in this degree at Jupiter's distance. The reason will be found in what was stated in the last paper respecting the brightness of Jupiter. He is almost three times as bright as a body equally large, and placed where he is, but having a surface of no greater reflective power than the moon's.

This leads us to the consideration that possibly a portion of the light of Jupiter may be inherent-in other words, that he may be glowing with the intensity of his own heat. Certainly the excess of his light is not sufficient to prove this, for as a matter of fact he only gives out as much light as he would reflect if his whole surface were covered with such clouds as ours. Still, as his light is seen in the telescope to be not uniformly white, but to owe its whiteness as a whole to a mixture of many distinct colours, while some of his belts present an actual

1 Everyone who has seen the moon by day, when there are small summer clouds in the sky under full illumination, must have noticed how much inferior the moon's brightness is to that of such clouds.

red colour, as though there were red-hot matter glowing underneath his vaporous envelope, the idea is strongly suggested that he may glow with some small degree of inherent light, and may be capable of supplying a considerable quantity of heat to the orbs which circle around him.

This is not so fanciful as perhaps many readers may at first suppose. If we imagine Jupiter to give out as much heat as though he were a globe as hot as iron when it is beginning to show red with increase of heat, he must warm at least his nearer satellites in an efficient manner. The quantity of heat he would supply to his nearest satellite would be that which a circular sheet of iron, one foot in diameter, and maintained at a dull red heat, would give out to objects two yards from it. This would be by no means a contemptible addition to the supply derived directly from the sun. And it is to be remembered that this heat and any accompanying light would be given out not only, like the reflected sunlight, when Jupiter is full, but whenever he is above the horizon. Thus may it be said of these moons, that

By tincture or reflection they augment

Their small peculiar, though for human sight

Too far remote.

Apart, however, from such considerations as these, it will be manifest that whatever differences may be pre sented in the moons of Jupiter as compared with our earth, the only known abode of life, are differences of

degree only and not of kind. They are not by any means of such a nature as to preclude the conception that life exists on these worlds.

If this be indeed the case, how wonderful must be the scene presented to the inhabitants of these moons by the great planet round which they circle! He must, in fact, replace with them the great object of our own wondering contemplation, the sun. For to them the sun is a minute body, showing a disc scarcely equal to one twenty-fifth of the sun's disc as we see him; but the glorious disc of Jupiter, varying at the several moons from an area 1,600 times as great as their sun, to an area 35,000 times his, and marked by the wonderfully beautiful colours of which our telescopes afford a faint idea, must be an amazing object of contemplation. The changes also which take. place in his aspect as he turns round on his axis, and also as real changes take place in his cloud envelope, must be singularly impressive and suggestive. We may well believe that if there are reasoning creatures on the worlds which circle around Jupiter, they have as good reason as we ourselves to say, 'The heavens declare the glory of God, the firmament showeth His handiwork.'

THE RING-GIRDLED PLANET.

I HAVE often thought that among the most instructive of those lessons which the celestial orbs teach us is the avoidance of rash judgments as to the ways and works of the Creator. We are so often mistaken when we judge by appearances. Some star or planet appears to our judgment inferior to the rest, either in size or brightness, or beauty of colour, and we should be apt to judge that it was among the least important of God's works; and lo, when we see it rightly, it is a miracle of beauty and symmetry, marvellous in its dimensions and in the complexity of its structure, and manifestly a scene where forces the most stupendous are daily and hourly in action.

Certainly there is no known orb which presents so strikingly the contrast I have referred to as the planet Saturn. To the naked eye this body is a dull-looking star, far inferior to Jupiter and Venus in apparent sizenay, even surpassed in lustre by Mars and Mercury, the least of the primary planets. Slowly he drags his course onward from station to station, his slow advance alternating with yet slower retrogression. He was chosen by the alchemists as the representative of the heavy and lustre