28 Transactions Tennessee Academy of Science. 



Some Remarkable PKenomena of tne Tor- 

 nado in Montgomer}? County, 

 Tennessee, April aq, 1909 



By James A. Lyon^ Southwestern Presbyterian University, 

 Clarksville, Tenn. 



The general atmospheric conditions favoring the occurrence of 

 tornadoes in the Mississippi Valley are fairly well known to 

 meteorologists, so that it is possible to predict from six to thirty- 

 six hours ahead, that tornadoes may be expected in certain gen- 

 eral regions. Thus the observer at Nashville, after studying the 

 telegraphic reports of weather conditions over the country, may 

 announce, at 8 a. m., "Look out for tornadoes in North Louisiana, 

 Arkansas and Mississippi this afternoon, and in Alabama and 

 Georgia tonight and tomorrow." But, as the exact locality where 

 a tornado is likely to occur cannot be predicted even within one 

 hundred miles, nor the exact time, within several hours, such pre- 

 dictions are of little or no practical value, and are not published, 

 as they would rather tend to terrify than to protect the people. 



It is well known that the general movement of the atmosphere 

 over the United States is from west to east, and that there is a 

 constant procession of great vortices or whirls, whose rotary mo- 

 tion is counter-clock-wise, drifting eastward in the general move- 

 ment of the air, like the eddies and whirls in the current of a great 

 river. These are properly called "Cyclones;' and are of great 

 size, measuring from 500 to more than 1,000 miles in diameter. 

 At the center of a cyclone the barometer is relatively "Low." 

 These cyclones are more marked in the winter and spring sea- 

 sons tlian at other times, and generally follow one another across 

 the country at intervals of about three days, and are separated 

 from one another by areas of high pressure, sometimes called 

 "anti-cyclones." 



