"'Let there be light,' said God, and forthwith light Ethereal, first of things, quintessence pure, Sprung from the deep, and from her native east To journey through the airy gloom began, Sphered in a radiant cloud, for yet the sun Was not: she in a cloudy tabernacle Sojourned the while. God saw the light was good, And light from darkness by the hemisphere Divided: light the day, and darkness night, He named. This was the first day, even and morn." The second day's work has been interpreted variously, according to the generally received science of the times of the various commentators who have dealt with it. Even in Milton, though the great poet rejected the earlier idea of a solid firmament, we find prominence given to that of a vast hollow sphere of "circumfluous waters," which, by encircling the atmosphere, kept aloof the "fierce extremes of chaos." Later commentators, such as the late Drs. Kitto and Pye Smith, hold that the Scriptural analogue of the _firmament_ here--by the way, a Greek, not a Hebrew idea, first introduced into the Septuagint--was in reality simply the atmosphere with its clouds. "The historian" [Moses], says Dr. Kitto, "speaks as things would have appeared to a spectator at the time of the creation. A portion of the heavy watery vapor had flown into the upper regions, and rested there in dense clouds, which still obscured the sun; while below, the whole earth was covered with water. Thus we see the propriety with which the firmament is said to have divided the waters from the waters." It is certainly probable that in a vision of creation the atmospheric phenomena of the second great act of the creation drama might have stood out with much greater prominence to the prophetic eye placed in the circumstances of a natural one, than any of its other appearances. The invertebrate life of the Silurian period, or even the ichthyic life of the earlier Old Bed Sandstone period, must have been comparatively inconspicuous from any sub-ærial point of view elevated but a few hundred feet over the sea level. Even the few islets of the latter ages of the period, with their ferns, lepidodendra, and coniferous trees, forming, as they did, an exceptional feature in these ages of vast oceans, and of organisms all but exclusively marine, may have well been excluded from a representative diorama that exhibited optically the grand characteristics of the time. Further, it seems equally probable that the introduction of organized existence on our planet was preceded by a change in the atmospheric conditions which had obtained during the previous period, in which the earth had been a desert and empty void. We know that just before the close of the Silurian ages terrestrial plants had appeared, and that before the close of the Old Red Sandstone ages, air-breathing animals had been produced; and infer that the atmosphere in which both could have existed must have been considerably different from that which lay dark and heavy over the