A. Guyot—Dry Zones in both Hemispheres. 168 
“Garua, furnishes moisture enough to render all hills and pas- 
tures green with verdure. In the latitude of the dry zone, 
however, from 20° to 80° S. lat., in the desert of Atacama, 
about the tropic of Capricorn the atmosphere is not only rain- 
less but perfectly dry. Even on the coast of Chili, Copiapo, 27° 
S. lat., receives only 0°32 inch of rain, La Serena in Chili 0°5 
inches. In the same lat. on the east of the Andes the plains of 
the Pampas are subject to great droughts. ’ e gran-seco 
(great drought) of nearly three years duration, which took 
place in this century, is still remembered as having cost the 
life of millions of cattle which came to die along the few river 
courses which had retained some water; leaving their bones 
accumulated just as the fossil bones of the Quaternary mam- 
mals are now found in the Pampas. 
Tn the same latitudes in Africa the Kalahari Desert extends 
over the whole western half of the continent an cae 
Australia the dry zone passes from west to east through the 
very center of the continent between the summer rains of the 
tropics and the winter rains of the more southern latitudes, 
with the exception of a narrow strip of the eastern coast which 
is watered by the winds from the sea; condensing rather scanty 
eo irregular rains-on the Blue Mountains and the Australian 
ps 
‘The existence in each hemisphere of a dry zone in the sub- 
tropical latitudes may thus be considered as a fact for which a 
cause must be found. On the other hand it is true that both in 
the northern and southern hemispheres notable interruptions 
are found, and it is to be remarked that they are all on the 
eastern side of the continents. In America from eastern Texas 
along the gulf to Florida the latitude of the dry zone has an 
abundance of rains. In the Old World from the Sind desert 
near the Indus through both Indian peninsulas and Southern 
China, the lands in the latitudes of the dry zone are still more 
plentifully watered. In the southern hemisphere the eastern 
half of South America and South Africa and the eastern coast 
of Australia, though moderately supplied, are not wanting in 
rain, especially near the sea. This apparent anomaly also has 
to be accounted for. a 
_ As among the causes which govern the aqueous precipita- 
tion the course of the winds occupies the first place, I am 
inclined to think that a close consideration of the normal move- 
ment of the atmosphere in the latitudes of the dry zones will 
“account for the above mentioned facts. _ ys 
(hese winds belong to two classes. In the first are those 
which form a part of the general circulation of the atmosphere, 
resulting from the spherical form of the globe. In the other 
“are itis mainly due to the relative distribution of continents 
