-1859] WRITINGS OP JOSEPH HENRY, 301 



The thunder storm differs from the tornado in its less con- 

 centration, and consequently in the less intensity of its vio- 

 lence. It occurs usually in the United States in the after 

 part of a sultry day, when the air has attained its maximum 

 amount of vapor, and has therefore assumed a condition of in- 

 stable equilibrium. These storms are usually produced over 

 a considerable extent of country on the same day, and occur 

 nearly at the same hour for several days in succession, and 

 probably serve to restore a more stable equilibrium to the 

 air, and thus perform the office of the great winter storms 

 which sometimes regularly succeed each other at given inter- 

 vals. Their general course is eastward, but they sometimes 

 deviate from this direction to a certain extent, apparently on 

 account of the attraction of water courses; they partially ex- 

 haust, carry up and precipitate the moisture of the atmos- 

 phere, but sometimes leave the air immediately afterwards 

 in a sultry condition. We hope to be able to give in another 

 article an exposition of the electrical phenomena exhibited 

 by thunder storms, but we may mention here the fact of the 

 almost instantaneous fall of rain after each peal of thunder. 

 It has been supposed that the drops of rain in this case were 

 produced by the agitation of the discharge of lightning; but 

 a little reflection will render it evident that the rain must 

 have commenced its rapid descent before the discharge took 

 place, since it follows the flash at so short an interval that 

 we must suppose that it commenced to fall previous and not 

 subsequent to the discharge. It is more probable that the fall 

 of rain, on account of offering a conducting medium for the 

 electricity, is the cause and not the consequence of the dis- 

 charge in question. 



The great interior storms we have mentioned usually com- 

 mence at the Far West, even at the base of the Rocky Moun- 

 tains, and generally occur in November, December, January, 

 February and March. They are sometimes of great extent 

 in a north and south direction. One of these storms, that of 

 1836, which was investigated with so much ability by Pro- 

 fessor Loomis, reached from the Gulf of Mexico to unknown 

 regions in the north. They are of varying breadth, some- 



