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Show ANNOTATIO 'S AND ADDITIONS. 151 are often hea.ru to ripple audibly (filets de courant), arc only perceptible in a dead calm (calme plat). (3"') p. 36.-"Increascs the sv.fjocating heat." I have observed in the Llanos de Apure, at the Guadalupe catLle 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 A pure had a temperature of 42° R. (126° Fahr. ). ( 36) p. 37 .-"The illusive image of a cool, rippling, watery mt"rror." 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 wavecovered 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 bas 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. 37.-"The .Melon Cactus." The Cactus melo cactus is often 10 to 12 inches in diameter, and has usually 14 ribs. The natural crop of Cactacere, the whole family of Nopalere of Jussieu, belong exclusively to the New Continent. ~'he cactuses assume a great variety of shapes: ribbed and melon-like (Melo cacti); articulated or jointed (Opuntire); forming upright columns or pillars (Cerei); serpentine and creeping (Rhipsa- |