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PROFESSOR JAMES THOMSON ON THE 
of that hemisphere, another covers the middle latitudes in which winds prevail from 
south of west in the northern hemisphere, and north of west in the southern, and the 
third covers the polar region. 
Now, attention for simplicity being confined to the northern hemisphere, explana¬ 
tions of the scheme may be continued as follows :— 
In the trade-wind zonal ring the bottom current flows from the Calms of Cancer as 
the Trade Wind to the Equatorial Belt and rises there, and flows then in the upper 
regions of the atmosphere till it comes to a situation aloft nearly over the Calms of 
Cancer, and thence it descends obliquely to the Calms at bottom to flow again 
towards the Equator, and so to begin another circuit alike in character to the one 
now described. Next in the zonal ring of the middle latitudes, according to the 
scheme, the current of air taken as beginning at the Calms of Cancer advances in the 
lower regions over the surface of the sea as a wind from south of west till it comes to 
about the Arctic Circle where it ascends to the upper regions, to begin a return 
course proceeding southwards as an upper current till it comes to places aloft nearly 
over the Calms of Cancer, thence to descend to those Calms below, and so to complete 
its circulation from some part of that belt back again to the same belt. Next as to 
the supposed circulation in the zonal ring of the Arctic Regions, it may suffice to say 
briefly that the lower current is asserted to be from the Pole and the upper current 
towards the Pole, the ascent from the lower to the upper being at or near to the 
Arctic Circle, and the descent being in a region closely surrounding the Pole, all as 
may be seen by inspection of the diagram. 
Ferrel, in setting forth in his paper his scheme of circulation and his theoretical 
reasonings on the subject, introduces as a fundamental principle in it the assertion 
