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.
3. Winds do not, and can not, “encounter.” They stratify upon each other. They are produced by the action of opposite electricity, and are connected together in their origin and action. The atmosphere is never free from the regular and irregular currents, however invisible for the want of condensation. Aeronauts find them in the most serene days. They exist without encounter or tendency to rotation, every where, and at all times; even over the head of the distinguished Professor, whether he sleeps or is awake. We can all see them when there is condensation, and it is rarely the case that there is not some degree of it in some of them.
4. That “Great region of expansion” is a chimera. It does not exist. It is a region of lower temperature, and of condensation, instead of expansion of aqueous vapor. The trade does not rise in it, or the S. W. wind overflow from it. See the table cited page [165].
5. The hurricanes do not originate in the surface trades, as he supposes. They originate in the belt of rains, the supposed “region of expansion,” and issue out of it; or in the counter-trade, where volcanic elevations rise far into or above the surface trade.
6. This hypothesis can not be sustained upon his own principles. The distance between Africa and the West India Islands, where most of the hurricanes originate, is from 2,500 to 3,000 miles. These gales are small when they commence, not ordinarily over one or two hundred miles in diameter, and often less. There are trades all the way over from Africa, and S. W. winds also, if they exist, as he supposes, in the West Indies. How can it happen that this lateral overflow should pass without effect, over 2,500 miles of S. W. wind and trade, and concentrating the overflow of a continent over one small and chosen spot of the West Indies, pitch down there, and there only, and crowd the S. W. wind into the trade below? This is too much for sensible men to believe.
What does Professor Dove mean by the term impulsion, as applied to the winds? How are they impelled? It is the fundamental idea of his calorific theory, that they are drawn by the suction caused by a vacuum, and the vacuum created by expansion and overflow above, in obedience to the law of gravity; that the S. E. trade is drawn to the great region of expansion, and the S. W. runs from it as an overflow. But if the S. W. is driven down into the plane and place of the surface-trades, how does it continue to be impelled, and why is it not then subject to the suction of the vacuum which draws the trade? Does that vacuum select its air, and so attract the trade, in preference to the depressed portion of the S. W. current, that the former runs around the latter to get to the vacuum, and the latter around the former to get away from it? And does the trade, when it has got around the S. W. current, instead of going to the vacuum, continue to gyrate, and the S. W. current, instead of pursuing its regular course, gyrate also about the trade, and both move off together, regardless of the vacuum of the great region of expansion, in a new direction to the N. W., in an independent, self-sustaining, cyclonic movement, increasing in power and extent, involving extended and increasing condensation, producing the most violent electrical phenomena, and thus continuing up, even to the Arctic circle? Yes, says Professor Dove. No, say all fact, all analogy, and his own principles.
7. His theory relative to the typhoons is unintelligible. If they originate near the lateral confines of the great region of atmospheric expansion, they originate in the region of the trade-winds, for the two are identical. How the direct pressure of the air from the trade-wind over the Pacific, in the more expanded air of the monsoon region, can occasion a typhoon upon any principles, passes my comprehension. If, as Lieutenant Maury supposes, the monsoons are reversed trades, then the trade-wind and monsoon region are identical. If the monsoons are found in the belt of rains, then, the trades, upon Professor Dove’s principles, pass into the monsoon region by attraction or suction, without pressure. Either way the theory is undeserving of consideration.
A new theory has recently been started by Mr. Thomas Dobson, and, although it is (like all other efforts to get the upper strata down to produce condensation, or those below up, that they may be condensed), without foundation, his collection of facts is brief and interesting. I copy his article from the London, Edinburgh, and Dublin Phil. Mag., for December, 1853. It adds to the collection of facts in relation to the connection between volcanic action and storms for the seventeenth century, made by Dr. Webster:
The following appear to be the main facts which are available as a basis for a theory which shall comprehend all the meteors in question:
1st. The eruption of a submarine volcano has produced water-spouts.