As the moon rises, heaven will be flooded with blue light, and one after another the stars will be submerged and lost, until only a solitary shining pinnacle of brightness will here and there remain out of the whole host of them. It is curious to think that, were the moon but a little brighter and truly the ruler of the night, rising to its empire with the setting of the sun, we should never dream of the great stellar universe in which our little solar system swims--or know it only as a traveller's tale, a strange thing to be seen at times in the Arctic Circle. Nay, if the earth's atmosphere were some few score miles higher, a night-long twilight would be drawn like an impenetrable veil across the stars. By a mere accident of our existence we see their multitude ever and again, when the curtains of the daylight and moonlight, and of our own narrow pressing necessities, are for a little while drawn back. Then, for an interval, we look, as if out of a window, into the great deep of heaven. So far as physical science goes, there is nothing in the essential conditions of our existence to necessitate that we should have these transitory glimpses of infinite space. We can imagine men just like ourselves without such an outlook. But it happens that we have it. If we had not this vision, if we had always so much light in the sky that we could not perceive the stars, our lives, so far as we can infer, would be very much as they are now; there would still be the same needs and desires, the same appliances for our safety and satisfaction; this little gaslit world below would scarcely miss the stars now, if they were blotted out for ever. But our science would be different in some respects had we never seen them. We should still have good reason, in Foucault's pendulum experiment, for supposing that the world rotated upon its axis, and that the sun was so far relatively fixed; but we should have no suspicion of the orbital revolution of the world. Instead we should ascribe the seasonal differences to a meridional movement of the sun. Our spectroscopic astronomy--so far as it refers to the composition of the sun and moon--would stand precisely where it does, but the bulk of our mathematical astronomy would not exist. Our calendar would still be in all essential respects as it is now; our year with the solstices and equinoxes as its cardinal points. The texture of our poetry might conceivably be the poorer without its star spangles; our philosophy, for the want of a nebular hypothesis. These would be the main differences. Yet, to those who indulge in speculative dreaming, how much smaller life would be with a sun and a moon and a blue beyond for the only visible, the only thinkable universe. And it is, we repeat, from the scientific standpoint a mere accident that the present--the daylight--world periodically opens, as it were, and gives us this inspiring glimpse of the remoteness of space.