750 THE POPULAR SCIENCE MONTHLY. 



progress of the cyclone proper across the country. They may occur 

 near, or in advance of, the cyclonic storm-center ; or they may appear 

 near the outer edge of the general disturbance, hundreds of miles 

 away. They usually develop within the area of highest temperature, 

 and are often preceded by a brassy sky, and hot, gusty winds, some- 

 times followed by a sultry atmosphere and an ominous calm. They 

 occur most frequently near the close of the day, their general direc- 

 tion being from southwest to northeast. They vary much in size and 

 force, but all have the same general characteristics in regard to ap- 

 pearance and action ; being a funnel-shaped cloud, heavily charged 

 with electricity, that goes bounding and whirling along in close prox- 

 imity to the earth's surface, dealing death and destruction wherever it 

 touches. The generally accepted belief is, that tornado-clouds are 

 formed suddenly, by the meeting of warm and cold currents of air ; 

 or, by the union of a positive with a negative cloud, a partial vacuum 

 being formed, constitutes the axis around which the cloud begins to 

 whirl, gathering strength and increased velocity as it goes. 



As the tornado now sweeps onward in its course, it rises and falls 

 with a series of bounds, and, with a swaying motion, describes a zigzag 

 course, now forming a chain of loops, and again shooting off on an 

 obtuse angle, varying in the speed of its forward motion, which may 

 be anywhere from ten to thirty miles an hour. At the same time it 

 is rapidly whirling on its axis in the opposite direction from a screw, 

 or the hands of a clock, the air revolving around the vortex necessarily 

 attaining a speed of several hundred miles an hour. First widening, 

 then contracting, now bounding above the tree-tops, and again de- 

 scending to sweep the earth bare of every object within its reach, the 

 aerial monster surges onward. The largest forest-trees, mere play- 

 things in its grasp, are plucked up by the roots, or snapped off like 

 pipe-stems ; substantial buildings are first crushed like egg-shells, then 

 caught up in the vortex and the debris carried sometimes for miles, 

 before it is again thrown off by centrifugal force, and falls by gravi- 

 tation anywhere, everywhere, as soon as released from the monster's 

 grasp. 



It is difficult accurately to describe the tornado's appearance and 

 work, even for those who have been eye-witnesses, or who have person- 

 ally passed through the horrors its coming brings. While accounts dif- 

 fer as to its appearance and behavior, as witnessed from different points 

 of observation and under different circumstances, all substantially agree 

 that it is cone-shaped, its motion rotary, that its apex resembles fire 

 and smoke, and that vivid lightning and heavy rain-fall usually ac- 

 company it. In rare instances, electricity, in the form of St. Elmo's 

 fire, will precede the vortex, and a white, steamy cloud will follow. 

 It will be observed that the form of the tornado-cloud is nicely illus- 

 trated by the " proof-plane " used in teaching natural philosophy. The 

 small end of the plane is most heavily charged with electricity, and, 



