The caravan halted. One of the Arab attendants had fallen upon the sands. He was the first to succumb to the sufferings of thirst, increased by the burning heat of the desert. Most of the men dismounted, and gathered around him, but they could do little for him. A loud shout from a couple of men on the camels caused the whole party to look up. The men pointed to the westward. Exclamations of delight burst from the lips of all; for there, not two miles away, lay an oasis, a palm grove in the midst of a clear lake, whose waters sparkled invitingly in the sunlight. [Illustration: A VISION OF DELIGHT.] Even the sick Arab turned his dim eyes thither, and his feeble lips uttered a faint cry of joy. The sight so revived him that he was able, lying on a camel’s back, to go with the others to this oasis. But, alas! the nearer they drew to the palm grove the more distant it appeared; and, at last, they lost sight of it altogether. Then the travelers knew it to have been a _mirage_, and they looked at each other in despair. But Calvert encouraged them. A mirage, he said, was a picture of some object painted in the air by the refraction of the sun’s rays through a peculiar atmosphere. It was a deceptive appearance, but it was caused by a real thing. In order to produce the picture of an oasis in the sky the oasis itself must be _somewhere_. True, it might be at a long distance from them; but he thought it more probable that it was quite near. And he indicated in what direction it was likely they would find it. Calvert spoke so earnestly that the courage of the party revived. They immediately started off again under his direction. And, after seven hours’ march, they did come upon a real oasis. Whether it was the one they had seen pictured in the air they did not know, but this was no matter. It was smaller than the picture, but images of things are often distorted. The sick Arab recovered after a couple of days’ rest, and the caravan renewed its march, men and beasts strengthened and refreshed. They took with them a liberal supply of water. At this oasis they also found guides, who conducted them into the regular caravan route; and they all arrived safely at Damascus. CORAL. Coral had been used many hundreds of years before men found out what it was. The savages used to fashion it into ornaments for their knife and axe handles; and, when men were more civilized, and had learned to work in iron, and to make armor, they liked to adorn their shields and helmets with coral. Women made of this beautiful red substance, necklaces for the neck, bracelets for the arms, and ornaments for the hair. But it is not likely that any of these savages or partially civilized people made any attempt to find out what kind of substance this coral was. They gathered it near the surface of the sea, and never stopped to think how it got there.