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 have become so far dispersed that not one of those which was first seen is now above the horizon, while other ships, not at first to be discerned, have come within sight.

These considerations illustrate the transient nature of the appearance of the starry heavens when we contemplate periods of time comparable with those which the facts of geology demand for the requirements of earth -history. It is quite true that for the convenience of the argument I have been obliged to take specific numbers and to assume certain conditions, but there can be no doubt that the illustration is sufficient for demonstrating that in the course of the next million years the disposition of the sidereal heavens must present a totally different appearance from what it now shows. By the same reasoning we feel assured that if a view of the heavens had been obtained from this earth a million years ago, it must have been totally different from that offered by our present skies. Conceive that a man were transported back to the time when those great forests were flourishing whose remains have been preserved in the form of coal. It is, I believe, practically certain that few, if any, of the stars that now adorn our skies would be then discernible by him. I do not mean to say that there were no stars visible at the time of the coal forests. It would be much more reasonable to suppose that the firmament was as richly spangled with gems then as it is now, but those heavens would not be the heavens which we know. The estimates of geological chronology generally received would place the date of the great coal forests at an epoch far more remote than a million years back. Indeed, if anyone were to maintain that the remoteness of the period had to be expressed in