Prevailing Currents of the Atmosph 305 
_-6. The sixth objection which I offer to the common theory of 
the trade winds, consists in the frequent occurrence, in our Ameri- 
can climate, of the highest summer heats for several days in suc- 
cession, sometimes irrespective of the immediate heat of the sun, 
which heated air, as appears from comparative observations, is 
mainly brought to us by geographical transfer along the earth’s 
surface, and which appears to depart in the same manner. ‘This 
could never happen if the most heated portions of the atmosphere 
necessarily ascend from the surface. A like objection is derived 
from the frequent interstratification and horizontal transfer of 
currents of unequal temperatures and hygrometrical conditions, 
which appear to move over great distances without any obvious 
change in their relative altitudes. 
Having already noticed; in the course of these remarks, the 
system of horizontal circuits of revolution pursued by the winds 
on each side of the equator, it is now only necessary that I refer 
the observers of the expedition to the particular delineations of 
these circuits, and of the alternating system of monsoon winds, 
on the maps which are furnished herewith.* 
It must not be supposed, however, that these circuits of revo- 
lution in the great winds, are generally uniform or strictly defined 
in their location or development, even on the open ocean. On 
the contrary, the winds which proceed outward from the trades, 
often overlie those which at the same time are returning into the 
trades, This often occurs extensively, on different meridians 
along the same parallel; besides the incidental fluctuations and 
disturbances to-which the winds are always liable, and the shitt- 
ing of their. field of revolution to the north or south, by the 
change of seasons. But the general result, is a continued and 
* 27 ny ee t . 
said to reign in it-all the year round. We shall find more than one opportunity to 
make the same observation.” cat bai 
“This relates to the southern Pacific in long. 110° to 115° west from Greenwich, 
and serves to show an extension of the westerly monsoon winds at that season, 
rvations have tended to con- 
umerous 
fimme the tenn ethene of these winds in the intertropical latitudes of the Pacific, 
, i er the whole western coasts 
opposite to the alleged course of the trade winds 
of intertropical America, 
* In the al of the maps referred to, some general notion of the system of 
xxv, p. 124-125. 
Vol. xv, No. 2.—July-Sept, 1843, 39 
