BIRTH OF THE TORNADO. 39 



METEOROLOGY. 



BIRTH OF THE TORNADO. 



CAPTAIN SILAS BENT. 



The prevailing winds of the Basin of the Mississippi are from the westward ; 

 being from the northwest in winter and from the southwest in summer. 



The westerly winds are cold, dry and compact, or heavy; whilst the south- 

 erly winds — especially if coming from the Gulf of Mexico — are warm, moist and 

 diffuse, or light. 



This marked meteorological difference in these winds, forbids their ready or 

 fluent commingling, but on the contrary, in fact, rather establishes a vital antag- 

 onism, between them, which leads to dire conflicts for supremacy wherever they 

 encounter each other during the transition seasons of spring and autumn ; at 

 which times, the atmospheric convulsions are often so great as to culminate in 

 most destructive storms. 



When these encounters take place, the north wind, owing to its greater 

 specific gravity, wedges under, or under-runs the lighter south wind and is thus 

 placed between the warm earth below and the still warmer south wind above, 

 and feeling the impulse of its increasing temperature, begins to expand, but be- 

 ing still pressed onward by its own volume in the rear and finding no escape, its 

 travail begins. 



Meanwhile, its own chilling effect upon the humid atmosphere above con- 

 denses and wrings out from the latter, torrents of rain. This rain in turn, how- 

 ever, is not unfrequently converted into heavy hailstorms before it reaches the 

 earth, by the rapid evaporations to which it is exposed in passing through the 

 cold, dry stratum of north wind beneath. 



The struggle thus begun, continues until the underlying cold wind finds a 

 weak spot in the stratum above, through which it makes a breach and bursts forth 

 with an upward force, proportioned to the pressure it is sustaining. 



An opening once made, the rush of the surrounding air towards the central 

 outlet — obedient to physical law — assumes a rotary and upward whirl, the vortex 

 of which is a vacuum, but whose substance becomes a writhing column of wind, 

 water and electric fire ; with its base resting upon the earth, but whose summit 

 reaches above the contending winds; and the Tornado has sprung into existence, 

 ready to start on its brief but terrible career of destruction and death ! 



In addition to this whirHng movement — the velocity of which is beyond com- 

 putation — the tornado at once takes place on an onward or progressive motion 

 over the earth's surface, whose path is probably the resultant of the relative 



