Fi tert Sua 
EF. Loomis— Contributions to Meteorology. 21 
Such an effect may be produced by an obstructing range of 
mountains, and if a district is completely surrounded by ranges 
of mountains, any strong upward movement of the air over this 
district seems impossible, unless from currents of air prevailing 
at an elevation greater than the summits of the surrounding 
mountains. Spain affords a remarkabie example of the opera- 
tion of this principle. This country is divided by numerous 
chains of mountains, one of which upon the north and north- 
west sides condenses the vapor coming in from the ocean, and 
presents a continuous belt of excessive rain-fall. But between 
the different ranges of mountains which traverse this country 
are small table lands almost entirely surrounded by mountain 
ranges, and these regions are marked by a great deficiency of 
rain. One of these is in the neighborhood of Salamanca, where 
the mean rainfall is only 9°45 inches, although at Santiago, 
distant less than 200 miles, the average annual rain-fall amounts 
to 67-60 inches. The extreme dryness at Salamanca does not 
seem to be due entirely to the great rain-fall upon the moun- 
tains situated on the western coast, because in many other parts” 
ol Murope (e. g. the coast of Norway) a similar rain-fall upon a 
range of mountains is not accompanied by an equal dryness 
upon the eastern side of the mountains. The dryness which 
prevails over the desert of Gobi is doubtless due in a great 
measure to the extreme precipitation upon the elevated moun- 
tains on the southwest, but this effect is aggravated by the in- 
fluence of the other mountain ranges by which Gobi is almost 
entirely surrounded. The small rain-fall which prevails on the 
east side of the Caspian Sea, is in part due to the influence of 
the Caucasus and other mountains on the southwest; but this 
effect is aggravated, as in the case of Gobi, by the mountains 
and high lands which enclose this region on every side except 
the northwest. The small rain-fall in Peru is obviously, the 
effect of the Andes upon the easterly winds which blow over 
em. 
‘satin of the Great Desert of Sahara. The prevalent winds 
Here are similar to those near the northern margin of the Sa- 
hara, and if a great continent stretched eastward from South- 
ern California without any considerable range of mountains, it 
is believed that it would show an immense desert similar to the 
Sahara. The small breadth of the American continent south 
of latitude 30°, together with the continuous chain of moun- 
tains which forms the great back bone of the American conti- 
