Before the existence of the earth, throughout an eternity, suns and worlds existed, peopled with beings like ourselves. Millions of years before the earth was, they were. The past of the universe has been as brilliant as the present, the future will be as the past, the present is of no importance. In examining the past history of the earth, we might go back to a time when our planet shone in space, a veritable sun, appearing as Jupiter and Saturn do now, shrouded in a dense atmosphere charged with warm vapors; and we might follow all its transformations down to the period of man. We have seen that when its heat was entirely dissipated, its waters absorbed, the aqueous vapor of its atmosphere gone, and this atmosphere itself more or less absorbed, our planet must have presented the appearance of those great lunar deserts seen through the telescope (with certain differences due to the action of causes peculiar to the earth), with its final geographical configurations, its dried-up shores and water-courses, a planetary corpse, a dead and frozen world. It still bears, however, within its bosom an unexpended energy—that of its motion of translation about the sun, an energy which, transformed into heat by the sudden destruction of its motion, would suffice to melt it and to reduce it, in part, to a state of vapor, thus inaugurating a new epoch; but for an instant only, for, if this motion of translation were destroyed, the earth would fall into the sun and its independent existence would come to an end. If suddenly arrested it would move in a straight line toward the sun, with an increasing velocity, and reach the sun in sixty-five days; were its motion gradually arrested, it would move in a spiral, to be swallowed up, at last, in the central luminary. The entire history of terrestrial life is before our eyes. It has its commencement and its end; and its duration, however many the centuries which compose it, is preceded and followed by eternity—is, indeed, but a single instant lost in eternity. For a long time after the earth had ceased to be the abode of life, the colossal worlds of Jupiter and Saturn, passing more slowly from their solar to their planetary stage, reigned in their turn among the planets, with the splendor of a vitality incomparably superior to that of our earth. But they, also, waxed old and descended into the night of the tomb. Χ Had the earth, like Jupiter, for example, retained long enough the elements of life, death would have come only with the extinction of the sun. But the length of the life of a world is proportional to its size and its elements of vitality.