Scientific Intelligence, — Meteorology. 421 



aurora projecting themselves upon a mountain which was at no 

 great distance from his vessel. This observation well merits 

 being confirmed and repeated. — Arago, 



4. On Winds. — The variations in the wind may supply me- 

 teorologists who are travelling, by land or by sea, many subjects 

 of the deepest interest. 



First of all it is important to ascertain concerning every place, 

 what is the direction of its prevailing winds, and what the differ- 

 ent epochs of the year during which each wind is most common. 



None of our meteorological instruments measures the velo- 

 city of the wind with any thing like desirable accuracy. When 

 the sky is quite overcast, the observer who wishes to ascertain 

 the rapidity of the progress of a tempest, finds himself reduced 

 to the necessity of throwing light substances into the air, and 

 with his watch in hand, following them with the eye till they at- 

 tain different objects, the distances of which are known. When 

 the sky is only partially covered with clouds, the course of their 

 shadow upon the earth, for ten seconds for example, will give 

 a very close approximation to the distances they have been 

 moved in that time by the power of the wind. 



The observation of these shadows, then, may be recommend- 

 ed with confidence ; they afford the velocity of the wind much 

 better than the use of light bodies, which scientific men have 

 been under the necessity of rejecting, because their movements 

 near the surface are complicated by the influence of innumerable 

 whirlwinds and counter-currents. 



In the year 1740, Franklin discovered that the hurricanes 

 which so often ravaged the western parts of the United States, 

 propagated themselves in a course contrary to the direction in 

 which they were blowing. Thus a hurricane from the north- 

 east might begin at New Orleans ; after a time it would arrive 

 at Charleston : and two or three hours later it would reach 

 Philadelphia ; then after many hours it would be felt at New 

 York, and at a still later period would reach the more northern 

 towns of Boston and Quebec, in all this course proceeding back- 

 wards, for it always blew from the northward. 



It results from this observation of Franklin that the hurricanes 

 of America are winds of aspiration. Is not the same phenome- 



