48 W. Ferrel—Oyclones, Tornadoes and Waterspouts. 
wou e determined by the ascending velocity of the air at 
different distances from the center. 
feet high and perhaps about thirty or forty feet in diameter at 
the top. The direction of rotation was the same as of storms of 
the northern hemisphere. Leaving the road the whirl passed 
out on the prairie, immediately filling the air with hay, which 
was carried up in somewhat wider spirals, the diameter of the 
cone thus filled with hay being about one hundred and fifty feet 
at top. It was then observed also that the dust column was 
hollow. Standing nearly under it, the bottom of the dust 
column appeared like an annulus of dust surrounding a circular 
area of perfectly clear air. The area grew larger as the dust 
was raised higher, being about fifteen or twenty feet wide when 
it was last observed.” (Nature, Sept. 11th, 1879.) 
