G80 
PROFESSOR JAMES THOMSON ON THE 
regions to a minimum height over the Equator remains in the diagram, but it is 
expressly eliminated by words in the accompanying text. This diagram, when cor¬ 
rected according to Mr. Ferrel’s printed words is, as may readily be seen, essentially 
the same as my own. 
In the closing passage of his second paper, 1860, Ferrel made mention of the 
theory given by me at the British. Association meeting in Dublin, 1857, but he did 
this with erroneous representation of the theory, and with inadequate recognition of 
its importance and of the fundamental changes he had made from his own previous 
theory in adopting the main features of mine and incorporating them with some 
remnants of his own previous views or modes of consideration. 
I proceed next to offer some considerations which, I think, may be of intrinsic 
interest in themselves, besides helping towards the development and elucidation of 
true theory in regard to atmospheric motions and other conditions. 
I have to mention, at this stage, that it may sometimes be convenient, as an 
aid towards brevity and clearness in expression, to characterize air which has no east¬ 
ward or westward motion relative to the Earth’s surface as having par, or being at 
par of revolutional velocity and, likewise, to use the designation over par of 
revolutional velocity to signify eastward relative motion, and under par to signify 
westward relative motion. 
(a.) Recalling to notice the theory of Maury and the first theory of Ferrel 
given in his 1856 paper, and drawing attention to the confluence supposed, under both 
these theories, of two great upper currents of the atmosphere meeting aloft over the 
belt called the Calms of Cancer in the Northern Hemisphere, and of other two 
currents likewise meeting over the belt called the Calms of Capricorn in the Southern, 
I think it is well to remark that, if such a confluence were to take place of two 
currents, one coming from higher latitudes and the other from lower to a zonal belt of 
meeting, the current from the higher latitudes would have a rapid westward motion 
relatively to the Earth below, that is, a revolutional velocity greatly under par, and 
the current from lower latitudes would have a rapid relative motion eastward, or, in 
other words, a revolutional velocity greatly over par. They would meet one another 
obliquely with a velocity of each relative to the other very great because of its having 
had no frictional mitigating resistance such as the Earth’s surface would afford to 
currents meeting in like manner at bottom of the atmosphere. Thus the belt of 
meeting aloft would be a place of extraordinary commotion, and this commotion would 
be propagated with the two descending currents down to the surface of the Earth 
below ; and thus, instead of the Calms of Cancer or Capricorn we ought to expect to 
find there a belt of wild and varying storms. This very simple, and, I think, very 
obvious principle, is one of the numerous objections which might singly or conjointly 
have checked both Maury and Ferrel in the early inception of their theories, and 
might reasonably have prevented them from propagating views so fallacious. 
(b.) Next we may raise questions, and proceed to solve them more or less completely. 
