I 



1874] WRITINGS OF JOSEPH HENRY. 423 



There is however a meteorological condition of the atmos- 

 phere during a north-east storm on our coast which appears 

 to me to have a direct bearing on the phenomenon in ques- 

 tion. It is this, that while a violent wind is blowing from 

 the north-east into the interior of the countrj', a wind of 

 equal intensity is blowing in an opposite direction at an 

 elevation of a mile or two. This is shown by the rapid east- 

 wardly motion of the upper clouds as occasionally seen 

 through breaks in the lower. 



As a further illustration of this principle I may mention 

 that on one occasion (in 1855) I started on my way to 

 Boston from Albany, in the morning of a clear day, with a 

 westerly wind. The weather continued clear and pleasant 

 until after passing the Connecticut river, and until within 

 fifty miles of Boston. We then encountered a storm of wind 

 and rain which continued until we reached the city. On 

 inquiry I learned that the storm had commenced in Boston 

 the evening before, and although the wind had been blowing 

 violently toward Albany for twenty hours it had not reached 

 inwardly more than fifty miles. At this point it met the 

 west wind and was turned back above in almost a parallel 

 current. This is the general character of north-east storms 

 along our coast, as shown by Mr. Espy, and is directly 

 applicable to the phenomenon mentioned by General Duane, 

 which must be accepted as a fact, though by no means a 

 general one applicable to all stations. While a violent wind 

 was blowing toward his place of observation from Cape Eliza- 

 beth at the surface of the earth, a parallel current of air was 

 doubtless flowing above with equal or greater velocity in the 

 opposite direction. The efifect of the latter would be to in- 

 crease the velocity of the upper part of the wave of sound, 

 and of the former to diminish it; the result of the two being 

 to incline the front of the wave of sound toward the observer, 

 or to throw it down toward the earth, thus rendering the 

 distant signal audible under these conditions when other- 

 wise it could not be heard. I think it is probable that the 

 same principle applies to other cases of the abnormal propa- 

 gation of sound. 



