"If we suppose the upper portions of the air ascending over Asia and Africa to flow off laterally, and if this takes place suddenly, it will check the course of the upper or counter-current above the trade-wind, and force it to break into the lower current. "An east wind coming into a S. W. current must necessarily occasion a rotatory movement, turning in the opposite direction to the hands of a watch. A rotatory storm, moving from S. E. to N. W., in the lower current or trade, would, in this view, be the result of the encounter of two masses of air, impelled toward each other at many places in succession, the further cause of the rotation (originating primarily in this manner) being that described by me in detail in a memoir 'On the Law of Storms,' translated in the 'Scientific Memoirs,' vol. iii. art. 7. Thus, it happens that the West India hurricanes, and the Chinese typhoons occur near the lateral confines on either side of the great region of atmospheric expansion, the typhoons being probably occasioned by the direct pressure of the air from the region of the trade-winds over the Pacific, into the more expanded air of the monsoon region, and being distinct from the storms appropriately called by the Portuguese 'temporales,' which accompany the out-burst of the monsoon when the direction of the wind is reversed." The analogy between this, and a theory of Mr. Redfield's, will be noticed further on. But I remark, in passing, that there is not a fact or inference in this paragraph which will bear examination. 1. There is no such regular S. W. wind over the surface trade, as he supposes. Doubtless, there are, occasionally, secondary S. W. currents between the counter-trade and the surface one, with partial condensation, for much of both becomes depolarized by their reciprocal action and precipitation, and these induced S. W. currents are sometimes so strong as to usurp the place of the surface-trade, and become very violent in the latter part of hurricanes; but such is not the usual course of the upper currents of the West Indies, as the progress of storms there, and observation, prove. 2. There can not be any _periods_ of extensive and _sudden_ expansion over Africa. If there is any place on the earth which has a more uniformly progressive temperature, either way, and is more free from _sudden_ extremes, or which is more arid and destitute of aqueous vapor, and sudden aqueous expansions, than another, it is Africa. No such occasional sudden expansions are there possible.