1874] WRITINGS OF JOSEPH HENRY. 389 



or from a point toward which the wind is blowing, they take 

 this as an infallible indication that in the course of from one 

 to five hours the wind will change to the opposite direc- 

 tion from which it is blowing at the time." The same state- 

 ment was made to me by the intelligent keeper of the fog- 

 signal at Block Island. In these cases it would appear that 

 the wind had already changed direction above, and was thus 

 transmitting the sound more in its own direction than that 

 of the wind at the surface of the earth. 



Another remarkable fact bearing on this same point is 

 established by the observations of General James C. Duane. 

 At Cape Elizabeth, 9 miles south-easterly from the general's 

 house, at Portland, is a fog-signal consisting of a whistle 10 

 inches in diameter; at Portland Head, about 4 miles from the 

 same city, in nearly the same direction, is a Daboll trumpet. 

 There can be no doubt, says the general, that those signals 

 can be heard much better during a heavy north-east snow- 

 storm than at any other time. " As the wind increases in 

 force, the sound of the nearer instrument, the trumpet, 

 diminishes, but the whistle becomes more distinct; but I 

 have never known the wind to blow hard enough to prevent 

 the sound of the latter from reaching this city." In this 

 case the sound comes to the city in nearly direct opposition 

 to the course of the wind, and the explanation which sug- 

 gested itself to me was that during the continuance of the 

 storm, while the wind was blowing from the northeast at the 

 surface, there was a current of equal or greater intensity 

 blowing in an opposite direction above, by which the sound 

 was carried in direct opposition to the direction of the sur- 

 face current. The existence of such an upper current is in 

 accordance with the hypothesis of the character of a north- 

 east storm, which sometimes rages for several days at a given 

 point on the coast without being felt more than a few miles 

 in the interior, the air continuously flowing in below and 

 going out above. Indeed, in such cases a break in the lower 

 clouds reveals the fact of the existence above of a rapid cur- 

 rent in the opposite direction. 

 The full significance however of this idea did not reveal 



