Page:Popular Science Monthly Volume 58.djvu/392

384 north and south to all points in the east between north and south, making all sorts of combinations, accelerating in speed, slowing up, sometimes standing still seemingly, but yet progressing surely, certainly, inevitably to the east.

The anti-cyclone, judging it wholly from its invariable surface effects, which can be seen day after day on the United States Weather Bureau's daily maps, is essentially a down-draught eddy or center of dispersion for the winds; an area where the barometric pressure is above the normal (Chart No. 1). The cyclone, also invariably, so far as the surface levels of the atmosphere go, is an up-draught eddy, a center of wind concentration; an area where the barometric pressure is below the normal (Chart No. 2). When it is remembered that the winds circulate outward from the high pressure center of an anticyclone spirally, from left to right, clockwise, while the winds move into the low pressure of a cyclone spirally, from right to left, counter clockwise, some idea of the simplicity of weather causation is gained. Remembering also that, by reason of the descent of relatively cool, dry air and its dispersion, the polar anti-cyclone is the cause of clear and cool weather phenomena, while by reason of the rushing in of warm, moist air on one side, its expansion and cooling as it rises, and cool, dry air on the other, the cyclone is the seat of storm phenomena, the first primary lesson in American weather is over.

Through a failure to grasp the greater synthesis of the weather, terminology and local storm differentiation have naturally become hopelessly muddled in the newspapers, though here the difficulty of grasping the facts is even less than in the first issue. The cyclone is the center of rhetorical disturbance, and inky clouds of misuse and abuse gather about it, since, as a parent of storms and as a weather-breeder of no mean type, the cyclone plays the dramatic leading rôle in American meteorology. It is not only itself capable of great development of storm energies in the winter, early spring and late autumn, but in its milder summer moments is particularly likely to be the parent of specific local disturbances. With one of these, the tornado, it is identified popularly by the newspapers, which, in spite of all explanation on the part of the Weather Bureau, have not yet seen the absurdity of applying to a secondary phenomenon, insignificant in size compared with-the primary eddy, the name of the general disturbance. The cyclone, sweeping along with warm, moist weather in front, clear and cool weather in its rear, attended by a general rain, and in its sphere of influence covering a dozen States or more, surely may be separated from the local tornadoes, which, though destructive and terrifying, are but mere local incidents in the parent circulation. This is so markedly shown in the weather map of March 27, 1890, that, once seen, it is incomprehensible how error can so hold its own (Chart No. 3).