118 THE PHYSICAL GEOGRAPHY OF THE SEA. 
gestions of the facts gathered from the sea as I had interpreted 
them, viz., that the trade-winds of the southern hemisphere, after 
arriving at the belt of equatorial calms, ascend and continue in 
their course toward the calms of Cancer as an upper current from 
the southwest, and that, after passing this zone of calms, they are 
felt on the surface as the prevailing southwest winds of the extra- 
tropical parts of our hemisphere ; and that, for the most part, they 
bring their moisture with them from the trade-wind regions of the 
opposite hemisphere. 
218. I have marked on Plate VII. the supposed track of the 
" Passat-Staub," showing where it was taken up in South Amer- 
ica, as at P, P, and where it was found, as at S, S ; the part of 
the line in dots denoting where it was in the upper current, and 
the unbroken line where it was wafted by a surface current ; also 
on the same plate is designated the part of the South Pacific in 
which the vapor-springs for the Mississippi rains are supposed to 
be. The hands (ly^) point out the direction of the wind. Where 
the shading is light, the vapor is supposed to be carried by an up- 
per current. 
Such is the character of the circumstantial evidence which in- 
duced me to suspect that some agent, whose office in the grand 
system of atmospherical circulation is neither understood nor rec- 
ognized, was at work in these calm belts. 
219. Dr. Faraday has shown that, as the temperature of oxygen 
is laised, its paramagnetic force diminishes, being resumed as the 
temperature falls again. 
" These properties it carries into the atmosphere, so that the 
latter is, in reality, a magnetic medium, ever varying, from the 
influence of natural circumstances, in its magnetic power. If a 
mass of air be cooled, it becomes more paramagnetic ; if heated, 
it becomes less paramagnetic (or diamagnetic), as compared with 
the air in a mean or normal condition."* 
220. Now, is it not more than probable that here we have, in 
the magnetism of the atmosphere, that agent which guides the 
air from the south 217) through the calms of Capricorn, of the 
equator, and of Cancer, and conducts it into the north ; that agent 
which causes the atmosphere, with its vapors and infusoria, to flow 
* Philosophical Magazine and Journal of Science, 4th series, No. 1, January, 1851, 
page 73. 
