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 fall of the Barometer by this cause, inferring, that at a certain height the rising air overflows the rest of the atmosphere, forming a ring of cloud vapor and air, which pressing on that below, occasions the rise of the barometer found at the edges of severe storms.

Mr. Thomas Hopkins of Manchester, in a work published in 1844, entitled “On the atmospheric changes which produce Rain, Wind and Storms,” admits with Mr. Espy the ascent and condensation of vapor in the air from various causes, and that all horizontal winds are thus produced. He considers also that the ascending winds produce descending ones, and that the rain produced in the higher regions brings air and vapor with it in its descent, and thus constitutes the lower atmospheric currents; and finally, that storms are produced by the same causes that produce other winds, and that the greatest storms are descending winds.

Dr. Alex. Thom. [sic], of H. M. 86th Regiment, in his book upon “Storms in the Indian Ocean, and South of the Equator,” is of opinion, that the cause of the rotatory motion in storms—is, at first, opposing currents of air on the borders of the monsoons and trade-winds, which differ widely in temperature, humidity, specific gravity, and electricity. These, he thinks, give rise to a revolving action which originates the storm, which subsequently acquires an intestine and specific action involving the neighboring currents of the atmosphere, and enabling the storm to advance through the trade-winds to its opposite limits.

He further inclines to believe that “as the external motion is imparted to the interior motion of the mass, and centrifugal motion begins to withdraw the air from the centre and form an up-current, the whole will soon be involved in the same vortical action.” The up-current he accounts for by the pressure being removed from the centre, when the air there increases in bulk, diminishes in specific gravity, and hence its upward tendency.

There is, however, another point of view in which some writers have considered the formation and continuance of