The first is the mirage, seen in the desert of Africa. M. Monge, a member of the National Institute, accompanied the French army into Egypt. In the desert, between Alexandria and Cairo, the mirage of the blue sky was inverted, and so mingled with the sand below, as to impart to the desolate and arid wilderness an appearance of the most rich and beautiful country. They saw, in all directions, green islands, surrounded with extensive lakes of pure and transparent water. Nothing could be conceived more lovely and picturesque than this landscape. On the tranquil surface of the lakes, the trees and houses, with which the islands were covered, were strongly reflected with vivid hues, and the party hastened forward to enjoy the cool refreshments of shade and stream, which these populous villages preferred to them. When they arrived, the lake, on whose bosom they floated, the trees, among whose foliage they were embowered, and the people who stood on the shore inviting their approach, had all vanished, and nothing remained but an uniform and irksome desert of sand and sky, with a few naked huts and ragged shrubs. Had they not been undeceived by their nearer approach, there was not a man in the French army who would not have sworn, that the visionary trees and lakes had a real existence in the midst of the desert. The same appearance precisely was observed by Dr. Clarke at Raschid, or Rosetta. The city seemed surrounded by a beautiful sheet of water, and so certain was his Greek interpreter, who was acquainted with the country, of this fact, that he was quite indignant at an Arab, who attempted to explain to him, that it was a mere optical delusion. At length, they reached Rosetta in about two hours, without meeting any water; and, on looking back on the sand they had just crossed, it seemed to them, as if they had just waded through a vast blue lake. A similar deception takes place in northern climates. Cities, battlements, houses, and all the accompaniments of populous places, are seen in desolate regions, where life goes out, and where human foot has never trod. When approached they vanish, and nothing remains but a rugged rock, or a misshapen iceberg.