On March 18, 1911. A three-story building whose first story is buried under twenty-six feet of snow] A _tornado_ (popularly miscalled a "cyclone") is an extremely violent vortex in the air, usually less than 1,000 feet in diameter. Besides its very rapid rotary motion, it has a progressive motion at a speed averaging forty or fifty miles an hour. Its position at any moment is marked by a black funnel-shaped cloud, which grows downward from the sky and does not at all times reach the earth. A waterspout at sea is an identical phenomenon, though usually less violent. Along its narrow path the tornado demolishes everything,--wooden houses are blown to splinters, trees uprooted or stripped of their branches, structures of heavy masonry laid in ruins. Something like a hundred lives are lost each year in these storms, on an average, and one of them (St. Louis, May 27, 1896) destroyed thirteen million dollars' worth of property. [Illustration: Courtesy of the Scientific American A WATERSPOUT NEAR BEAUFORT, N. C., IN AUGUST, 1911] [Illustration: TURPAIN'S THUNDERSTORM RECORDER Or ceraunograph. This is one of several instruments designed to register the natural electric waves, or "strays," which sometimes interfere seriously with the transmission of wireless telegrams. Strays are often generated by lightning discharges, near or distant, and this instrument therefore serves to give notice of an approaching thunderstorm] A _blizzard_ is a high, cold wind, accompanied by blinding snow, which in winter sometimes blows out of the front of an advancing anticyclone, especially in our North-Central States. A similar wind, with or without snow, is called in Texas a _norther_. A _chinook_ is a warm, dry wind that descends the eastern slope of the Rocky Mountains in Montana, Wyoming and Colorado, and flows north-eastward over the plains. Its effects are most pronounced in winter, when it brings about a very sudden rise in the temperature--in extreme cases as much as forty degrees in fifteen minutes! It causes snow to vanish as if by magic, and is appropriately nicknamed the "snow-eater." "_Cloudburst_" is merely a picturesque name for a very heavy shower; usually a thunder-shower. [Illustration: IN THE WAKE OF A TORNADO The tornado destroyed a house and barn, but left a path in the center with practically no harm done]