Prevailing Currents of the Atmosphere. 307 
and veering to E. S. E. or S. E., than has been generally imag- 
ined. 
But the courses traversed by storms, in the trade-wind latitudes 
of the western Atlantic, and in corresponding latitudes in the 
western portions of other seas, as shown by my own inquiries 
and those of Col. Reid, I conceive to have proved this horizon- 
tal course of atmospheric circulation, in the clearest manner; and. 
it was this kind of evidence which first brought conviction to my 
own mind.* In pursuing this branch of the evidence we are thus 
able fully to establish the western half of the north Atlantic cir- 
cuit of revolution in the general winds; while, the better defined 
courses of the regular winds from the latitude of Madeira to the 
trades, in the eastern Atlantic, is such as to remove all reasona- 
ble doubt of a nearly continuous circuit of revolution, from left 
to right, around the region of extratropical calms, called the horse 
latitudes. 
I may add, on this occasion, that if further proofs were wanting 
of this horizontal circuit of revolution in these general winds, it 
is found in the rotation of the great storms, from right to left in 
the northern hemisphere, around their several moving axes, while 
pursuing their natural course of progression in this great aerial 
circuit. The question has often been asked, why should all these 
storms revolve in this direction, rather than in the opposite? 
And why the contrary rotation which is noticed in the southern 
hemisphere?) Now I have been convinced for several years, that 
this law results from the conditions which necessarily attend the 
earth’s rotation. For, in the westwardly movements of the at- 
mosphere upon the earth’s surface, obliquely from the equator 
towards the poles, the narrowing of the meridional spaces and the 
reduced velocities of rotation in the earth’s crust on the parallels 
newly arrived at by the surface wind, with the constant retarda- 
tions of eastern movement in the front of the mass which results 
* See my published maps of 1830 and 1835 containing the tracks of storms; also, 
my communications in Silliman’s Journal and the Nautical and Naval Magizines, 
since April, 1831; likewise, the charts &c., of Col. Reid, R. E., published in the 
Professional Papers of the Royal Engineers, and his elaborate work on the Law 
of Storms, issued at the time these remarks were in preparation ; a copy of which 
work was received and forwarded to the expedition. More recently the labors of 
Mr. Piddington of Calcutta have afforded much additional evidence, as relates to 
the Indian and China seas. 
