"The layers of the air," I replied, "are unequally warmed, and their refraction, which causes the rays of light to deviate in their course, reverses the objects which cover the plain, and, on the other hand, causes them to appear more elevated than they really are." "So we see water in a place where in reality there is none." "You don't take the sky into account, which is reflected on the ground beneath us as in a mirror. But the air is becoming cooler, and you will soon see the phenomenon slowly disappear, as if some invisible hand was pushing the mist back towards the horizon." [Illustration: "The moon rose, . . . and rendered the illusion more striking."] While we were looking down over the plateau, and watching the mirage gradually fade away, a distant light suddenly shone out. Loud exclamations hailed the sight of this unknown bivouac; and, fixing our eyes on it, we all formed endless conjectures. We had not expected to meet with any habitation before the next day; and the cry of "land!" on board ship after a long voyage could not have made a stronger impression than the sight of this fire. The air was cool; still l'Encuerado was not allowed to kindle a light, which would perhaps have betrayed us to foes. It was now twenty days since we had met with a human being, and our first feeling, after the instinctive joy at the idea of seeing our fellow-creatures, was, alas! one of distrust. [Illustration] [Illustration] CHAPTER XX. THE MORNING AND NIGHT DEW.--THE TERRE-FROIDE.--WATER-SPOUTS AND WHIRLWINDS.--THE BARBARY FIG-TREES.--THE CACTUS-PLANTS.--THE VIZNAGA.--OUR HOPES DISAPPOINTED.--DON BENITO COYOTEPEC. The sun had not risen when we were up and ready to start. We shivered with cold, for on the great plateau which we had now reached, to which the inhabitants of the lower regions give the name of _Terre-Froide_, the mornings are frosty. The profound darkness was succeeded by a dim twilight, afterwards by a fog, which penetrated our clothing as much as rain. "There has been no shower," cried Lucien, "and yet we are all wet." "It is the dew, Chanito; it is almost as abundant as the night dews in the _Terre-Chaude_." "Are not morning and night dews the same thing?" "Not exactly," I replied; "the morning dew is generally of a beneficial nature; but the Mexicans dread the other, which falls after sunset, and is said to be productive of fever." "But from whence does all this moisture come?" "From the air, which always contains a certain quantity, some of which it deposits on the ground, on stones and plants, as they become cool by radiation."