B. TERRESTRIAL PHYSICS AND METEOROLOGY. 95 



current of air flowing from all directions toward the central 

 funnel had a horizontal diameter of at least twenty miles 

 at the surface of the earth, and probably ten miles at the al- 

 titude of the lowest clouds. The diameter of the funnel at 

 the surface of the ground varied from fifty to seven hundred 

 yards. Its form could be distinguished up to the height of 

 between one and two miles by observers who were favorably 

 situated. The vortex of extreme violent winds varied from 

 nothing to one hundred yards, having an average diameter 

 of about thirty yards. Although the preceding dimensions 

 of the funnel are deduced from more or less reliable observa- 

 tions, yet Sergeant Mcintosh concludes that, in view of the 

 optical delusions incident to such observations, he is justified 

 in considering that the height of the funnel was, at the very 

 utmost, only a few hundred feet. Some observers saw only 

 one funnel; others saw two funnels superimposed with the 

 two narrow ends together, while a good many saw two and 

 even three funnels side by side. The evidence on all these 

 points is beyond question. He considers that, in general, 

 the smaller and lower end of the funnel moved onward in a 

 very irregular manner, and, on the average, lagged behind 

 the advancing cloud overhead ; new centres of condensing 

 vapor, and of consequent rarefaction of the air, were con- 

 tinually forming in advance of the moving funnel, so that 

 new funnels were formed near the surface of the earth, and 

 joined themselves to the cloud above, while the lower end 

 of the old funnel was dissipated, thus giving rise to an ap- 

 parent swaying of the funnel, from side to side, and forward 

 and backward. The tornado traveled in an east-northeast 

 direction, varying its course, however, every few miles, ac- 

 cording as it neared lakes, rivers, or open fields. Its average 

 velocity of progress appears to have been about twenty-nine 

 miles per hour. The wind blew in spirals to the centre of 

 the vortex ; the direction of revolution being contrary to 

 the hands of a watch throughout the whole course of the 

 storm. All who saw the funnel unite in describing it as cir- 

 cular, and whirling in the direction described. Besides its 

 horizontal motion, the wind had necessarily an ascending mo- 

 tion. At one place the angle of ascent was about 45. In 

 the black funnel itself the inclination was at least as great, 

 and probably greater. Twenty-six well-defined cases are 



