Page:Popular Science Monthly Volume 58.djvu/393

Rh The simplest study of the invariable facts shows that the tornado is a small eddy, superinduced under favorable meteorological and topographical conditions in the outer circulation (southwest to southeast quadrant) of a general low area disturbance (cyclone). It is of extreme intensity, the rotary motion of its winds around the central core (vortex) being inconceivably swift (100 to 500 and perhaps 1,000 miles an hour), but is limited as to duration—it lasts, at the longest, but a few hours; limited as to the width of path, this may vary from fifty to five hundred yards, one of a mile in width being exceptional, and limited as to the length of track, which if it exceeds 100 miles is unusual. Now, a cyclone is continental in magnitude, and may travel for weeks, going two-thirds of the way around the globe. Just as the cyclone's path is determined by interaction of barometric stresses in the general drift of the whole atmosphere, so the path of tornadoes is determined by the interaction of currents in the cyclonic drift. Individual tornadoes do not cross the country intact, as so many weather quacks prophesy, but the parent cyclone that conditions a number of them in the Western States one day, having traveled further east the next day, if local conditions allow, may superinduce similar local outbursts in the Middle States.

Thunder-storms, as a rule, are familiar enough and definite enough to escape the general muddlement, but even they have not escaped the tendency to 'cyclonize' every weather phenomenon. Hence the old-fashioned thunder-gust, the familiar straight outrush of the thunder squall, sometimes destructive, figures nowadays as a 'cyclone,' a 'tornado,' or mayhap a 'hurricane.' Not only this, but the thunderstorms that occur along the line of change from the warm front of a cyclone to the cooler rear—a cool anti-cyclone following—are accused of causing the anti-cyclone when they are an effect of the advancing anti-cyclone and not its cause, any more than the cow-catcher is the cause of the approach of a train.

Above all, the most extraordinary pother and confusion prevail over another storm type, the hurricane or tropical cyclone. Here the newspapers are seconded in their obscurantism by writers of books on the West Indies or the Philippines, all of whom should know better, or could know better if they only so elected. The hurricane—the typhoon is its Asian congener—though the smallest of cyclones, since its diameter usually ranges from 100 to 500 miles, is easily differentiated from the biggest tornado, since the latter diameter at the greatest barely reaches one mile. As the tornado in its narrow swath kills tens and hundreds, so the hurricane, with vast areas of sea and land swept by the besom of its great winds and washed by its tremendous storm wave, runs the death total up to the hundreds and thousands. The hurricane does not originate in the circumpolar drift, but is a