In his “Conduct of Life” Emerson has an essay on “Illusions” in which he describes the semblance to midnight skies paved with stars which the guide produces in the Mammoth Cave by hiding himself and throwing the rays of his torch athwart the ceiling set thick with transparent rock crystals. The effect is quite startling. For the moment it is hard to resist the conviction that you are actually looking upon the cloudless sky at night. But in reality is not the noonday sky just as much of an illusion, except that there are no mimic stars? The blue dome overhead is an illusion. There is no dome there. The sky is a mere apparition. It is not a body or a reality as it seems to be; it is mere empty space, though it has the effect upon us of a vast blue dome. How genial and inviting it looks when we see it peeping through the clouds, and how glorious when we see it swept free from clouds! Its purity, its serenity, its elevated character, move us to regard it as the abode of superior beings. The telescope dispels our illusions; the sky is not a transparent realm, but only an extension of earthly conditions. Heaven, the abode of the blest, takes its name from this negation of vacancy. Our notions of a personal God are similar illusions. God is as real as the sky is, and no more so, even though in our devout moods we lift our eyes heavenward and identify him with this comforting illusion. All our life illusions brood over us. The night is only a shadow--the negation of light; and yet it plays a part in our lives as real as that of health or friends or climate, as real, but of another kind. Time itself is an illusion. The future does not exist nor the past; yet how are our lives influenced by the memory of the one and our anticipations of the other!