106 A. S. Whitfield on Tornadoes in the Southern States. 
This will plainly appear from a diagram. Let a circle be de 
scribed representing the rim of a tornado. Then let two lines — 
be drawn, one representing the resultant of the forces of the 
southern currents, and the other the resultant of the forces of 
the northern currents, each deflected as it approaches the vortex, — 
but the former more than the latter. Each will maintain its 
owes a 
TE gee ee 
cloud-formation. In the Tuscaloosa tornado the gyration had | 
formed and travelled three-and-a-half miles when the first flash | 
occurred, | 
n is due, at any time before June, to the effect of the solar 
rays in our own latitude, and therefore answer the necessary 
condition of a stratum heated uniformly over a large are& 
Our tornadoes consequently do not grow out of the heat ray 
that penetrate our latitude, but ceili from the heat of 
tropics, transported hither in the winds; and this is the reason 
of their appearance either in the daytime or night. We never 
witness them in the hot summer, because then the lower atmos 
phere is warmed by direct rays, and a uniform temperature — 
over a wide extent, is impossible, from the fact that the cleared 
lands and forests, hills and valleys, are heated unequally, giv 
ing rise to ascending columns and moderate storms. If the 
theory of Espy were true, then July, August, and September 
* 
