"What vast flocks of birds!" exclaimed Mrs. Woolridge.
"Those are flamingoes, just rising from their resting-place," added the captain. "They were white just now as we looked at them; notice the color of the inside of their wings, which are of a rose-tinted pink."
"But what became of the wheat-fields that were here?" asked Mrs. Blossom, after they had observed the wild birds for a time.
"The sea broke in and covered the rich lands with sand and salt; and there are towns buried there now."
"Goodness, gracious!" almost screamed Mrs. Blossom. "There's another steamer sailing on the land!"
"It appears to be so, but is not so," replied the commander.
"It is really so," added Mrs. Woolridge; and all the party gazed with interest at the phenomenon.
"Only apparently so," the captain insisted.
"Please to explain it to us, Commodore," said Miss Blanche, who had long ago applied this title to him.
"With pleasure, Miss Woolridge. It is the mirage, from the Latin _miror_, to wonder, which appears to be what you are doing just now. The steamer you see sailing along the shore is an optical illusion, a reflection, and not a reality. Refraction, which is the bending of the rays of light, produces this effect. If you look at a straight stick set up in the water, it will appear to be bent, and this is caused by refraction. The learned gentlemen present will excuse me for going back to the primer of physics."
"We are quite satisfied to have the memory refreshed," replied the doctor.
"The air around us is of different densities, which causes the rays of reflection of our ship to be bent, sending the image up on the shore. What sailors call 'looming,' often seen on our own shores, is produced in the same way; and we often see an island, or a vessel, looming up away above the water, from which it is sometimes separated by a strip of sky. The mirage is often seen in the desert, with a whole caravan up in the air, sometimes upside down.
"An object is often seen when at a considerable distance from it. In the Arctic regions ships below the horizon, or hull down as sailors phrase it, are revealed to other ships far distant by their images in the air. From Hastings, on the English Channel, the coast of France, fifty miles distant, from Calais to Dieppe, was once seen for about three hours. In 1854 a remarkable exhibition of the mirage was witnessed in the Baltic Sea from the deck of a ship of the British navy. The whole English fleet, consisting of nineteen sail, distant thirty miles from the point of observation, were seen up in the air, upside down, as if they had been hung up there by their keels.