THE POWERS OF THE AIR.
IN the course of the last fifty years the progress of science has curiously illustrated the significance of the old saying that truth is often stranger than fiction. The good steed Bayard would be eclipsed by the iron horse as the darts of Orion are distanced by a Minié ball, and the dolphin-riding guest of King Periander would be glad to exchange his seat for the steerage-berth of a Cunard steamer.
Still greater, perhaps, would be the surprise of the mystic Bodin, if he could see how far the discoveries of the nineteenth century have surpassed anything dreamt of in the philosophy of his speculations on the acts of the "Invisible Powers." Invisible disease-germs are known to decide the question of life and death for countless thousands of our fellow-men. Invisible currents of a mysterious force carry our messages with & speed immeasurably superior to that of the best broom-bestriding witch, and the " empty air' has been found to possess potencies exceeding those of all the twenty-seven varieties of aërial demons enumerated by the author of "The Enchanted World."
After a few years' cruising in the eastern Mediterranean, Sir Charles Napier became inclined to "doubt if the mariners of Greece and Rome ever experienced such a thing as a genuine tornado;" but only since the establishment of meteorological observatories have even the navigators of the West begun to realize the force exerted by a common ocean gale. The storms of the northern Atlantic have béen known to reverse the current of the tides and to upheave the waters of vast ocean-areas with a force equal to a pressure of sixty billion pounds to the square mile. Storms originating on the plains of our central States have more than once reached the east shores of our continent, crossed the Atlantic, and swept over a considerable portion of Europe and western Africa, overcoming the resistance of all counter-currents and displacing a bulk of atmospheric strata that could not have been more than momentarily moved by the explosion of a mountain of gunpowder.
Air-currents, with their incalculable influence on the climatic conditions of our planet, have, indeed, been recognized as the most potent of all elementary agencies, and it is curious that the manifold inquiries into the proximate causes of their disturbances have as yet not led to more definite results. Dové and Redfield, the discoverers of several important atmospheric laws, suppose storms to be analogous to the eddies formed near the points of contact of two different river-currents, and assume the existence of established storm-routes, corresponding to the deflections of permanent equatorial and polar waves. Storms, however, are by no means confined to the region of the permanent air-currents (trade-winds, etc.), and are notoriously apt to follow a protracted calm. Recognizing the local and, as it were, abrupt origin of many storms, Prof. Espy tried to explain them on the following hypothesis. "Whenever the vapor of the atmosphere," he says, "is condensed into clouds or rain, the heat thus generated will rarefy the surrounding air-strata, thus causing them to rise upward and leave a vacuum which is speedily filled by inrushing air-currents from all sides. Hence the fact that the gusts of a cyclone blow from every quarter towards the centre of the storm." That theory, however, has not yet
