But if an even balance was restored yesterday, the opposite scale kicked the beam this morning. Not a speck of vapor blurred the spotless crystal of the sky, as I walked along the hanging paths of the Alameda. The sea was dazzling ultra-marine, with a purple lustre; every crag and notch of the mountains across the bay, every shade of brown or gray, or the green of grassy patches, was drawn and tinted with a pencil so exquisitely delicate as almost to destroy the perspective. The white houses of Algeciras, five miles off, appeared close at hand: a little toy-town, backed by miniature hills. Apes' Hill, the ancient Abyla, in Africa, advanced to meet Calpe, its opposing pillar, and Atlas swept away to the east ward, its blue becoming paler and paler, till the powers of vision finally failed. From the top of the southern point of the Rock, I saw the mountain-shore of Spain, as far as Malaga, and the snowy top of one of the Sierra Nevada. Looking eastward to the horizon line of the Mediterranean, my sight extended so far, in the wonderful clearness of the air, that the convexity of the earth's surface was plainly to be seen. The sea, instead of being a plane, was slightly convex, and the sky, instead of resting upon it at the horizon, curved down beyond it, as the upper side of a horn curves over the lower, when one looks into the mouth. There is none of the many aspects of Nature more grand than this, which is so rarely seen, that I believe the only person who has ever described it is Humboldt, who saw it, looking from the Silla de Caraccas over the Caribbean Sea. It gives you the impression of standing on the edge of the earth, and looking off into space. From the mast-head, the ocean appears either flat or slightly concave, and æronauts declare that this apparent concavity becomes more marked, the higher they ascend. It is only at those rare periods when the air is so miraculously clear as to produce the effect of _no air_--rendering impossible the slightest optical illusion--that our eyes can see things as they really are. So pure was the atmosphere to-day, that, at meridian, the moon, although a thin sickle, three days distant from the sun, shone perfectly white and clear.