GRAND CURRENTS OF ATMOSPHERIC CIRCULATION. 
683 
the principal flow towards the Equator takes place in the bottom lamina—the lamina 
whose motions constitute the winds noticeable by action on the sails of ships. So we 
may suppose that the main body of that great under-current blows nearly due west¬ 
ward with only a small component of motion equator-ward. I could not venture, 
through theoretical considerations alone, to form an opinion as to the velocity of 
westward relative motion which might thus be attained to in the main body of the 
great under-current, or the velocity of westward relative motion which might remain 
in some parts of the upper current proceeding from the Equator before it has made 
much advance in latitude to places importantly nearer the Earth’s axis. The com¬ 
plications involved in the frictional conditions attendant on the flow of sheets of air 
with others below and with others above going at very different velocities render the 
question practically unsolvable by theory alone. But I have to point out emphatically 
that the Dolclrum air, deadened as it is to the condition commonly spoken of as 
equatorial calm, is very approximately at par of revolutional velocity, and when it 
rises to the top, or to the very high regions, of the atmosphere, it will have scarcely 
any westward relative motion, and therefore will not be able to make its way thence 
as an upper current pole-ward except by flowing as we may say down hill, or as we 
may better say, among isobaric interfaces down-sloping forward. The lower part of 
this sheet of deadened air departing aloft pole-ward, and which lower part is much 
below the top of the atmosphere, and is in close contiguity with the current of 
westward relatively moving air (already just now mentioned) commencing to move 
pole-ward without ever having attained to par of revolutional velocity, will we may 
suppose, by buffeting and commingling between it and that westward relatively 
moving air, be dragged forward from the Equator, even among up-sloping isobaric 
interfaces, in a manner that may be likened to being dragged up hill. 
I might at present extend the explanations and reasonings on this matter some¬ 
what further, but I abstain from doing so in order not to prolong unduly the present 
paper. I prefer to leave the subject over for further consideration and exposition by 
myself, perhaps, and probably by others. 
(cl.) I propose next to offer some considerations in respect to the atmosphere of the 
polar regions. For simplicity of expression I shall speak, in particular, of the polar 
regions of the Northern Hemisphere ; and I intend that in this, as indeed throughout 
nearly all I have said in the present paper, the complications introduced into 
atmospheric motions by local distinctions of the Earth’s surface into land and sea are 
to be, primarily at least, disregarded. 
I consider that we should take as one element of our theories the principle that 
we have to suppose a stagnation of impounded air around the Pole over a great 
extent of the Polar Regions, this impounded air being maintained by the influx along 
the surface of the Earth of air frictionally deprived of the over-par of revolutional 
velocity which is possessed by the great cap of air higher up above the surface of the 
Earth. This impounded air lags, I affirm, in the Polar Regions, being unable, for want 
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