-18591 WRITINGS OP JOSEPH HENRY. 291 



uniformly has this been the case during the last year, that 

 we have been enabled to decide whether it would be proper 

 to advertise during the day the lecture to be given in the 

 evening. 



In summer it frequently happens that thunder storms 

 commence their course at points intermediate between Cincin- 

 nati and Washington, and therefore it will not always fol- 

 low that a clear sky in the morning at the former place will 

 indicate a clear evening at the latter. But wherever the 

 thunder storm commences it always moves eastward, or 

 rather eastward inclining to the north, a direction which 

 indicates that the direction of these circumscribed storms is 

 principally governed by the motion of the lower stratum of 

 air. 



The extent of the interior storms, north and south, is ex- 

 ceedingly variable. In some cases a storm of not more than 

 a hundred miles in width travels eastward along the lakes ; 

 and again at another time a storm of a similar width may 

 commence at the south and move along the shore of the 

 Gulf of Mexico. Again at other times the commotion ap- 

 pears to extend from some northern point in the British pos- 

 sessions, down to the Gulf of Mexico, and even farther south, 

 and to move eastward, side foremost. In this motion the 

 southern part of the storm first reaches the Atlantic Ocean, 

 in the southeastern part of Georgia, and since the general 

 trend of the coast is to the northeast, it is evident that the 

 storm will appear to move from south to north along the 

 coast, while in reality the whole system of disturbance is 

 moving eastward, and will finally leave the continent at New- 

 foundland. 



Another system of interior disturbances — which commenc- 

 ing apparently at the south and confined principally to the 

 eastern coast tends to draw in the air from the Gulf Stream 

 along the surface, to be carried outward again by the upper 

 current, — gives rise to our northeast storms. These are how- 

 ever in a great degree intercepted by the Alleghany Moun- 

 tains, and do not extend very far into the interior. Accord- 

 ing to a suggestion of Dr. Hare, these storms are due to a. 



