The earth is every day overspread with the veil of night for the same reason as the cages of birds are darkened,--namely, that we may the more readily apprehend the higher harmonies of thought in the hush and quiet of darkness. Thoughts, which day turns into smoke and mist, stand about us in the night as lights and flames: even as the column which fluctuates above the crater of Vesuvius, in the daytime appears a pillar of cloud, but by night a pillar of fire.