Situation of Zones without Rain, and of Deserts. 85 
distance of the sun, the atmospheric refrigeration arrives at 
a certain point. 
This being the case, we can easily understand that be- 
tween these two inverse regions, and at places to which the 
sun approaches most nearly, that is to say, towards the tro- 
pic, there may be a persistence of heat sufficient to maintain 
in solution the vapours transported by the influence of the 
trade-winds, so that there will be an absence of rains, 
and a simultaneous production of deserts, at least, if orogra- 
phical causes do not produce local coolings, or if special 
winds, by their alternate play, do not give rise to disturb- 
ances in the normal arrangement. Examples in support of 
this are sufficiently numerous ; and if we endeavour to ap- 
ply to Asia data resulting from the phenomena of Africa and 
America, we shall immediately find that that continent can- 
not contain deserts, properly so called, or, at all events, ab- 
solute deserts, such as the Sahara. 
A meridian passing along the eastern coast of Africa, in 
some measure divides the globe into two hemispheres: the 
one, the western, in which the trade-winds prevail, and the 
other, the eastern or Asiatic, forming the domain of the mon- 
soons; but these latter, from what has been said of the coast 
of Brazil, do not appear to be capable of producing perma- 
nent droughts, for such can only be the result of the uni- 
formity of the trade-winds. 
As, however, a series of deserts is generally indicated in 
that part of the world, it is of consequence to define them 
properly, in order that they may be reduced to their just 
value. 
The distribution of these deserts may be considered in two 
points of view. According to the one, they would commence 
opposite the Sahara, and would be prolonged in a straight 
line towards the east, following the tropic of Cancer, over a 
part of Arabia, of Syria, of Persia, and of India, where they 
would be interrupted by the edges of the plateau of the Dec- 
can. Over this extent of country, in which they are almost 
contiguous to one another, they would only be interrupted for 
a short space by the Red Sea, by the Persian Gulf, or by the 
mountains of Kurdistan and of Persian India, and their total 
