292 WRITINGS OF JOSEPH HENRY. [1855- 



heating and rarefaction of the air in the Gulf of Mexico, as 

 probably are also the " northers " which descend from the 

 western plains. 



Still another system of storms, originating in the Caribbean 

 Sea and following the general direction of the Gulf Stream, 

 sometimes sweep over the peninsula of Florida, and over- 

 lap somewhat upon the eastern coast of the United States. 

 These are the great hurricanes, — (or cyclones as the}'' are 

 sometimes called,) the character and nature of which have 

 given rise to so mucii discussion. 



During the warm months of summer almost every part 

 of the United States is occasionally visited with very violent 

 though exceedingly circumscribed commotions of the atmos- 

 phere known, as tornadoes or water spouts. These generally 

 move in nearly the same direction, — toward the northeast, 

 except perhaps on the borders of the Gulf of Mexico, leav- 

 ing their narrow path, sometimes only a few rods wide, 

 marked with the evidence of energetic action of a most de- 

 structive intensity. The question naturally arises, is it pos- 

 sible in the present state of science to give a rational explana- 

 tion of the various commotions (apparently fitful and complex 

 and without an adequate cause) manifested in the light and 

 invisible aerial covering of our globe? Can the question be 

 answered? How is it possible that the soft and balmy air, 

 which offers scarcely the least resistance to the motion of a 

 lady's fan, can yet exert a power sufficient to level with the 

 ground the largest trees of the forest in a single minute, to 

 the number of 7,000 in the space of a square mile, and this 

 devastating energy continue, as it has been known to do, for 

 a distance of many miles? 



The phenomena of these violent circumscribed storms, 

 which appear peculiarly marked in America, have been inves- 

 tigated with much careful and laborious research by Frank- 

 lin, Bache, Loomis, Olmsted, Hare, Redfield, Espy, and others. 

 We owe to the lamented Professor Mitchell, of North Caro- 

 lina, valuable suggestions in regard to the motions of the 

 air in storms of this character. Professor Bache was the 

 first to make an actual survey of the track of a tornado, and 



