478 CAUSES OF ARIDITY AND MOISTURE. Chap. XXIV. 



rain on the Kalahari Desert is caused by the mass of air losing 

 its humidity as it passes up, and glides over the subtending 

 ridge, and will turn to the map, he may perceive that the 

 same cause is in operation in an intense degree by the moun- 

 tains of Abyssinia to render the region about Darfur still 

 more arid ; and that the flanking ranges mentioned, lie much 

 nearer the equator than those which rob the Kalahari of hu- 

 midity. The Nile, even while running through a part of that 

 region, receives remarkably few branches. Observing also that 

 there is no known abrupt lateral mountain-range between 6° 

 and 12° S., but that there is an elevated partition there, and 

 that the southing and northing of the south-easters and north- 

 easters probably cause a confluence of the two great atmospheric 

 currents, he will perceive an accumulation of humidity on 

 the flanks and crown of the partition, instead of, as elsewhere, 

 opposite the Kalahari and Darfur, a deposition of the atmos- 

 pheric moisture on the eastern slopes of the subtending ridges. 

 This explanation is offered with all deference to those who have 

 made meteorology their special study, and as a hint to travellers 

 who may have opportunity to examine the subject more fully. 



ticity, they cause a considerable degree of cold, and a precipitation of 

 humidity in the form of fogs, clouds, rain, or snow. A similar effect 

 occurs whatever be the obstacle they find in their way. Now, this is 

 what had gradually taken place before 1856. By some cause or other 

 connected with the currents of the atmosphere, the warm current from 

 the west had annually ascended northward, so that, instead of passing 

 through France, it came from the Baltic and the north of Germany, thus 

 momentarily disturbing the ordinary law of the temperatures of Europe. 

 But in 1856 a sudden change occurred. The western current again passed, 

 as before, through the centre of France. It met with an obstacle in the 

 air which had not yet found its usual outlet towards the west and south. 

 Hence a stoppage, a rising, a consequent dilation and fall of temperature, 

 extraordinary rains and inundations. But now that the natural state of 

 things is restored, nothing appears to prognosticate the return of similar 

 disasters. Were the western current found annually to move further 

 north, we might again experience meteorological effects similar to those 

 of 1856. Hence the regular seasons maybe considered re-established in 

 France for several years to come. The important meteorological com- 

 munications which the Imperial Observatory is daily establishing with the 

 other countries of Europe, and the introduction of apparatus for measuring 

 the velocity of the aerial currents and prevailing winds, will soon afford 

 prognostics sufficiently certain to enable an enlightened Government to 

 provide in time against future evils." 



