684 
ON THE GRAND CURRENTS OF ATMOSPHERIC CIRCULATION. 
of revolutional momentum, and accompanying want of centrifugal inertial tendency, to 
take part readily in the great circulation between polar and equatorial regions. In fact, 
it cannot get out from its imprisonment there except by being dragged away through 
gradual entanglement with the comparatively rapidly revolving air arriving by the 
great upper current from regions having more rapid revolutional motion and passing 
away in the great middle return current towards the Equator. 
(e.) Further, I may now offer some considerations as to whether, according to 
theory, we should expect very clear skies to prevail in the Polar Region of impounded 
deadened air. I think we must suppose the great upper atmospheric current con¬ 
verging towards the Pole and having over-par of revolutional velocity must be already 
very dry, owing to its greatly reduced pressure and cold temperature. So, when its 
air descends in level to return towards the Equator, that air must, I think, be greatly 
under its saturation point with water-substance ; or, in other words, must be far from 
ready to form clouds, or to precipitate rain or snow. We have to recollect that 
descending air is generally very rainless. 
On the other hand the bottom flow along the surface of the land and sea converging 
towards the Pole I affirm to be moist. It will be from lower latitudes and generally 
warmer climates, and will carry moisture with it from sea and land. This bottom 
current will supply water-substance for cloud and snow in the impounded deadened 
polar air. The cold of radiation out to interstellar space, coupled with expansion in 
ascending before it can join the great middle current of return towards the Equator, 
will cause clouds and snow. 
I will now conclude this paper by offering a sketch of a contemplated experimental 
apparatus for affording practical illustration of the theory of Atmospheric Circulation 
which I have propounded. 
The apparatus would consist mainly of a horizontal circular tray kept revolving 
round a vertical axis through its centre. The tray would be filled to some suitable 
depth with water. Heat would be applied round its circumference at bottom, and 
cold would be applied or cooling would be allowed to proceed in and around the 
central part at or near the surface. Under these circumstances I would expect that 
motions would institute themselves, which would be closely allied to those of the 
great general currents supposed under the theory to exist in either hemisphere of the 
Earth’s atmosphere. The motions of the water, I would propose, should be rendered 
perceptible to the eye by dropping in small particles of aniline dye, and perhaps by 
other contrivances. Great variations would be available in respect to the velocity of 
rotation given to the tray, and in respect to the depth of water used, and the intensity 
of the heating and cooling influences applied. By various trials with variations in 
these respects I think it likely that the phenomena expected could be made manifest. 
