He caught up a fowling-piece which had belonged to his friend the purser, and handed Frank the fourth gun, an ordinary seaman’s carbine. “Now then, Nick, lead the way.”
Gilbert complied, and the whole party stepped out briskly, their curiosity, as well as their interest, being strongly awakened. They toiled through the heavy sand, which was only varied by heaps of drift-wood flung up by the sea, and the rotten carcasses of mud fish, which had been carried too far inland by the tide to be able to recover their native element. The stench, under the burning sun, was almost insupportable, and the three adventurers were greatly relieved, when, after a walk of three-quarters of an hour, the desert of sand was passed, and they ascended a rocky plateau, where some crags, twelve or fifteen feet in height, afforded at least some shelter from the rapidly increasing heat. “We are getting near the place now,” observed Nick, as they reached the last of a long chain of rocks, and came upon a wide and apparently level plain, but so much enveloped in mist as to be very imperfectly discerned.
“There it is, I declare,” exclaimed Frank, who was the first of the party to turn the corner of the limestone shelf. “There it all is—houses, fortifications, and soldiers, just as Nick said!”
There, indeed, it was. At the distance, as it seemed, of scarcely more than three hundred feet, were seen distinctly the battlemented walls of a city of great size and strength. There were the gateways, the flanking towers, and the embrasures; while behind them rose domes and cupolas, and the sharp-peaked roofs of numberless houses, intermingled with lofty trees. Under the walls ran a broad river, the waters of which rippled brightly in the sunshine, and upon its banks long lines of infantry were drawn up, or what appeared to be infantry, all standing silent and motionless as so many statues.
The two boys gazed in the utmost bewilderment at this spectacle, while Lion bounded forward, evidently meditating a plunge into the cool and sparkling waters. The astonishment of the party was in no way diminished, when the doctor, raising his gun to his shoulder, fired directly at the nearest platoon of soldiers, one of whom was seen to fall. The next moment the whole of his companions rose with loud screams into the air, and dispersed themselves in all directions. Almost at the same moment the walls and battlements of the fortress and ridges of roof behind them wavered and shook, and finally vanished from the scene, as the smoke of a wood fire is lost in the surrounding atmosphere. In their place appeared a low serrated ridge of rock, on which a few stunted shrubs were growing, while in front and behind alike extended the interminable waste of sand.
“Here is your soldier, Nick,” said the doctor, as he picked up the carcass of a large flamingo, which his shot had brought down. “Here’s his red cap and jacket—his beak and wings, that is to say—and here are his white facings—his neck and chest. You are not the first by a good many that has made that mistake!”
“This is what is called a mirage, then?” said Frank. “I’ve often heard of it, and longed to see it; and it is a more extraordinary delusion than I could have supposed possible. Why that low line of rock there, and those dwarf shrubs looked as if they were at least sixty feet high. How in the world do you account for it, Mr Lavie? Why even Lion was taken in!”
“I am afraid I cannot give you an explanation, which you will understand very clearly, Frank. It is caused by the inequality of the temperature in the lower strata of the air; which again is the result of the reflected heat of the sun’s rays on the barren, sandy plain. While the strata are unequally heated, these curious reflections, which are like those seen in broken mirrors, continue to deceive the eye. Objects appear to be raised high into the air, which in reality are to be found on the surface of the earth, often too they are immensely magnified, as indeed you saw just now; a single stone will seem the size of a house, and an insignificant shrub look as big as a forest tree. But when the sun gains sufficient power to raise all the strata to a uniform heat, the mirage melts away.”
“But your shot seemed to disperse it just now.”
“So it did. But my shot only disturbed the strata; and if the mirage had not been nearly on the point of vanishing, from the increasing solar heat, I doubt whether the same effect would have followed. But it is time for us to go back to our hut and finish our work. Nick, I suppose you will join us? We may see pretty plainly for ourselves that there are no fishermen’s huts in this quarter.”