If we look up at the sky with the eye of knowledge we can read in the celestial objects with which it is strewn something of the history of our earth. We can only read it dimly even with the aid of the greatest telescopes, and it is quite possible that in some respects we may read it wrongly. Let us, however, consider what the eye and the telescope will reveal to us. The eye will see the Sun--a great ball, into which the earth might sink without greatly altering the Sun's appearance, and surrounded with flaming gases hotter than the hottest furnace man has ever been able to contrive. In that heat every solid thing on the earth would melt and be turned into vapour. The eye will also perceive the Moon--another ball, much smaller than the earth, surrounded by no gases at all, having as far as can be seen no water; and being so cold during its long nights that all gases and liquids of which we know would be frozen solid there. The eye can also see a myriad of stars of varying brightness, but for the most part only thus distinguishable. If the telescope be now called in to aid, the eye will, however, be able to discern differences and distinctions in the stars. It will see that some are balls like the Earth, the Sun, and the Moon. If these balls are studied attentively we shall discover that one of them, Jupiter, is a great deal hotter than the earth, though a great deal cooler than the Sun; and that another of them, Mars, is a great deal colder than the earth, but a great deal warmer than the Moon. Perhaps we might now begin to surmise that the Sun coming first, Jupiter next, the Earth next, Mars next, and the Moon last, were all like stages in the history of one of these balls; and that, for example, any one ball began by being as hot as the Sun, and ended, after passing through stages like Jupiter, the Earth, and Mars, in being as cold and lifeless as the Moon.