The singular phenomenon of these “sand spouts,”--something analogous to which may occasionally be seen on a small scale in Europe where four roads meet,--is particularly characteristic of the Peruvian Sand Desert between Amotape and Coquimbo. Such a dense cloud of sand or dust may prove dangerous to the traveller who does not cautiously avoid its approach. It is also worthy of notice that these partial conflicting currents of air only arise when the air generally is perfectly calm. The aerial ocean resembles the sea in this respect, for in the latter also the small currents which are often heard to ripple audibly, (filets de courant), are only perceptible in a dead calm (calme plat). [35] p. 18.--“_Increases the suffocating heat._” I have observed in the Llanos de Apure, at the Guadalupe cattle farm, the thermometer rise from 27° to 29° Reaumur (92°.7 to 97°.2 Fahr.) whenever the hot wind began to blow from the Desert, which at such times was covered either with sand or with short withered turf. In the middle of the sand-cloud the temperature was for some minutes 35° R. (111° F.). The dry sand in the village of San Fernando de Apure had a temperature of 42° R. (126° Fahr.) [36] p. 18.--“_The illusive image of a cool rippling watery mirror._” The well-known phenomenon of the mirage is called in Sanscrit the “thirst of the gazelle.” (See my Relation historique, T. i. pp. 296 and 625; T. ii. p. 161.) All objects appear to hover in the air, and are at the same time seen reflected in the lower stratum of air. At such times the entire desert assumes the aspect of the wave-covered surface of a wide spread lake. Palm trees, cattle, and camels, sometimes appear inverted on the horizon. In the French expedition to Egypt, the soldiers, parched with thirst, were often brought by this optical illusion into a state of desperation. This phenomenon has been remarked in all quarters of the globe. The ancients were acquainted with the remarkable refraction of the rays of light in the Lybian Desert. I find mention made in Diod. Sic. lib. iii. p. 184, Rhod. (p. 219, Wessel), of extraordinary illusive images, an African Fata Morgana, with most extravagant explanations of the supposed conglomeration of the particles of air. [37] p. 19.--“_The Melon-Cactus._”