The Winds of Kimberley. 95 
‘The answer is simple. If the units be yards the mean height of 
each cube would be 10-2 yards, and there would be a measurable 
difference between the pressure at this height and that at the 
bottom.. Hence the expansion by heating would be easier upwards 
than outwards. On the other hand, the contraction by cooling 
would be more energetic inwards near the ground than downwards, 
resulting in an indraught throughout the whole cool hemisphere, and 
thereby assisting to some extent the outward expansion opposite. 
It seems scarcely likely that the excess of upward over outward 
expansion can extend to the highest limits of the atmosphere, but it 
is not unlikely that much of it intermixes with the constant north- 
westerly current above, in the cloud strata, and is thus drawn off as 
an outflow. If, however, expansion be wholly upwards, and con- 
traction wholly downwards, the base of each cube will at first 
remain unaltered in size and shape, together with the pressure upon 
it, the tops of the cubes rising by different amounts, but also remain- 
ing in a surface of equal pressure ; and no transfer of air can ensue, 
either above or below, until the high crest of the expanded air falls 
away from its altitude. Curiously enough, von Siemens maintains 
that in a surface of equal pressure, such as that in which our 
expanded and contracted cubes are supposed to lie, there can be no 
sliding away down the slope of equal pressure by the higher portions. 
The statement is doubtless only statically true, for it leaves out of 
account the fact that a free particle on an expanding surface is by 
the mere acquisition of motion projected by the earth’s rotation into 
an elliptical orbit with a focus at the earth’s centre of gravity. Con- 
sequently the atmospheric chimney must tend to bend over at the 
top in the direction of the equator, giving relief to the pressure at its 
base. The total effect is probably not great, yet it may partially 
explain the differences in the two calculated results above. On the 
whole, the case for an actual spiral outflow near the ground, from 
the hot to the cold hemisphere, seems to be not only possible, but 
very probable. 
