478 
CAUSES OF ARIDITY AND MOISTURE. Chap. XXIV. 
rain on the Kalahari Desert is caused by the mass of am 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 Kile, even while running tlirough 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 oj)portunity 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 may be 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 ap)paratiis for measuring 
the velocity of the aerial currents and prevailing winds, will soon afford 
prognostics sufficiently certain to enable an enhghtened Government to 
provide in time against future evils.” 
