470 RESEARCHES IN SOUND. 



tralized. The results also exhibited, in a striking manner, the diverg- 

 ency of sound from the axis of the trumpet, the trumjiet being heard in 

 the line of its axis in front at 6 miles and behind at 3, the winti being 

 nearly the same in both cases. 



All the observations were repeated on land with the artificial ear as 

 far as the unfavorable condition of the surface would permit. Although 

 the limit, as to distance, at which the sand might be moved was not in 

 most cases observed, yet the relative degree of agitation at a given dis- 

 tance established clearly which was the most powerful instrument, the 

 result giving precisely the same order of penetration of the different in- 

 struments as determined by direct audition. 



During this series of investigations an interesting fact was discovered, 

 namely, a sound moving against the wind, inaudible to the ear on the 

 deck of the schooner, was heard by ascending to the mast-head. This 

 remarkable fact at first suggested the idea that sound Avas more readily 

 conveyed by the upper current of air than the lower, and this apiieared 

 to be in accordance with the following statement of Captain Keeney, 

 who is commander of one of the light-house A^essels, and has been for a 

 long time on the bauks of Newfoundland in the occupation of fishing : 

 "When the fishermen in the morning hear the sound of the surf to the 

 leeward, 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 direction from which it is blowing at 

 the time." The same statement 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 transmit- 

 ting the sound in an opposite dkection to 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 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 DaboU trumjiet. There 

 can be no doubt, says the general, that those signals can be heard much 

 better during a heavy northeast 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 exi)lanation 

 which suggested 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 surface current. The existence of such an upper 

 current is in accordance with the hypothesis of the character of a north- 



