Page:Popular Science Monthly Volume 58.djvu/399

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The only difference between the conditions that caused the Louisville and near-by tornadoes and those that superinduced the St. Louis tornado and near-by outbreaks, on May 27, 1896, was in degree, not in kind. The March cyclone of 1890 was extensive in area and of great intensity; the parent cyclone of May 27, 1896, was a vague low area of the mild summer type, with a pressure at the center of only 29.70 inches, covering several States, St. Louis being in its southeast quadrant in the afternoon. The tornadoes this vague, weak cyclone set up in numerous localities were very destructive, the losses of life in and about St. Louis reaching to over 300 killed, with property losses of $12,000,000. The parent cyclone moved northeast and was central over the Lakes between Lake Huron and Lake Ontario on the afternoon of the 28th, with an increase in intensity, its center having a pressure of 29.40 inches, and, as local conditions allowed, it

caused a handful of small tornadoes in Maryland, Pennsylvania and New Jersey, as well as a large number of thunderstorms.

4.—This chart gives the track of four destructive tropical cyclones, known colloquially as 'hurricanes.' The hurricane differs from the continental cyclones of the North Temperate Zone in its surface effects in nothing but its intensity. The wind circulation is true to the cyclonic type (the term 'cyclone' was invented to describe the movement of the winds in the tropical tempest), but reaches great velocities, and, whereas the barometer in an intense continental cyclone may only fall to 29 inches in the tropical cyclone, its vortex may record 28 inches, and, in certain cases, the barometer has fallen to 27. In consequence of this, the vortical velocity of the wind is very great, reaching in gusts a rate of 80, 90, 100 and 125 miles an hour. As one of these tropical eddies advances from the West Indies and moves up the Atlantic Coast, it gives all localities north of its center, successively, gales from the northeast. These August-September, northeast gales, erroneously called 'equinoctials,' are but a part of the hurricane's