The optic deception of the rarefied and transparent atmosphere of these
elevated plains is truly remarkable. One might almost fancy oneself
looking through a spy-glass; for objects often appear at scarce
one-fourth of their real distance--frequently much magnified, and more
especially much elevated. I have often seen flocks of antelopes
mistaken for droves of elks or wild horses, and when at a great
distance, even for horsemen; whereby frequent alarms are occasioned. A
herd of buffaloes upon a distant plain often appear so elevated in
height, that they would be mistaken by the inexperienced for a large
grove of trees.

But the most curious, and at the same time the most tormenting
phenomenon occasioned by optical deception, is the "mirage," or, as
commonly called by the Mexican travellers, "the lying waters." Even the
experienced prairie hunter is often deceived by these, upon the arid
plains, where the pool of water is in such request. The thirsty
wayfarer, after jogging for hours under a burning sky, at length espies
a pond--yes, it must be water--it looks too natural for him to be
mistaken. He quickens his pace, enjoying in anticipation the pleasures
of a refreshing draught; but, as he approaches, it recedes or entirely
disappears; and standing upon its apparent site, he is ready to doubt
his own vision, when he finds but a parched sand under his feet. It is
not until he has been thus a dozen times deceived, that he is willing to
relinquish the pursuit, and then, perhaps, when he really does see a
pond, he will pass it unexamined, from fear of another disappointment.

The philosophy of these false ponds I have never seen satisfactorily
explained. They have usually been attributed to a refraction, by which
a section of the bordering sky is thrown below the horizon; but I am
convinced that they are the effect of reflection. It seems that a gas
(emanating probably from the heated earth and its vegetable matter)
floats upon the elevated flats, and is of sufficient density, when
viewed obliquely, to reflect the objects beyond it; thus the opposing
sky being reflected in the pond of gas, gives the appearance of water.

As a proof that it is the effect of reflection, I have often observed
the distant knolls and trees which were situated near the horizon beyond
the mirage, distinctly inverted in the "pond." Now, were the mirage the
result of refraction, these would appear on it erect, only cast below
the surfa