468 ARTESIAN WELLS IIST THE DESEET. 



indefinite hnman progress liardly expects that man's cunning will 

 accomplisli the universal fulfilment of the prophecy, " the desert 

 shall blossom as the rose," in its literal sense ; but sober geogra« 

 phers have thought the future conversion of the sand plains of 

 Northern Africa into fruitful gardens, by means of artesian wells, 

 not an improbable expectation. They have gone farther, and 

 argued that, if the soil were covered with fields and forests, vege- 

 tation would call down moisture from the Libyan sky, and that 

 the showers which are now wasted on the sea, or so often deluge 

 Southern Europe with destructive inundation, would in part be 

 condensed over the arid wastes of Africa, and thus, without fur- 

 ther aid from man, bestow abundance on regions which nature 

 seems to have condemned to perpetual desolation. 



An equally bold speculation, founded on the well-known fact 

 that the temperature of the earth and of its internal waters in- 

 creases as we descend beneath the surface, has suggested that 

 artesian wells might supply heat for industrial and domestic pur- 

 poses, for hot-house cultivation, and even for the local ameliora- 

 tion of climate. The success with which Count Lardarel has 

 employed natm-al hot springs * for the evaporation of water 



sandstone. Many a cliff in Arabia Petrsea is as manifold in color as the rain- 

 bow, and the veins are so variable in thickness and inclination, so contorted 

 and involved in arrangement, as to bewilder the eye of the spectator like a disk 

 of party-colored glass in rapid revolution. 



In the narrower wadies the mirage is not common ; but on broad expanses, 

 as at many points between Cairo and Suez, and in Wadi el Araba, it mocks 

 you with lakes and land-locked bays, studded with islands and fringed with 

 trees, all painted with an illusory truth of representation absolutely indis- 

 tinguishable from the reality. The checkered earth, too, is canopied wifh a 

 heaven as variegated as itself. You see, high up in the sky, rosy clouds at 

 noonday, colored probably by reflection from the ruddy mountains, while 

 near the horizon float cumuli of a transparent, ethereal blue, seemingly balled 

 up out of the clear cerulean substance of the firmament, and detached from 

 the heavenly vault, not by color or consistence, but solely by the light and 

 shade of their salient and retreating outlines. 



* Although hot springs, sometimes of considerable volume, are numerous, 

 yet the districts in which they occur are generally of small extent, and the 

 absolute quantity of water discharged by the hot springs of the earth may be 

 treated as insignificant in comparison with that derived from springs of ordi- 

 nary temperatures, by which most rivers are fed. The temperature of common 

 springs varies little from the mean atmospheric temperature of the locality, 

 and hence it is clear that the rain which feeds these springs does not descend 



