164 A. Guyot—Dry Zones in both Hemispheres. 
and oceans and participating therefore in the nature of the mon- 
soons. ‘To the first, I believe, the scarcity of rain in the dry 
zones must be attributed; to the others the abundance of 
rain in the well-watered portions of the same zones, which inter- 
rupt the continuity of the dry lands. 
of the atmosphere vast masses of air which overflow on 
sides toward the temperate zones, causing an accumulation of 
air about the 30th degree of latitude, enhanced still more by 
the decrease of the areas poleward. This accumulation is. 
shown by the existence of a belt of high barometric pressure, 
which there reaches the maximum known on the surface of the 
trades and the southwesterly winds characteristic of the tem- 
perate zones. e part, however, which each of these bodies. 
of winds plays in the condensation of rains is very unlike; the 
first brings drought; the second is the principal source of the 
rains of the temperate latitudes. 
t may, at first sight, appear singular that these two branches 
of the same aerial current should have so different an effect on — 
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