186 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



moving over the surface of the earth, the lower part moves 

 with less velocity on account of friction than the upper part, 

 and that consequently the tendency would be to tilt the sound- 

 wave so as to throw the sound downward toward the earth 

 in the case of the sound moving in the same direction as the 

 wind, and to deflect it upward in case the movement is in an 

 opposite direction, throwing it into the air above the head of 

 the observer. This hypothesis gives a ready explanation of 

 all the phenomena observed, and was fully illustrated by a 

 series of experiments made by Professor Henry in the vicinity 

 of the light-ship off Sandy Hook last summer. Two steam- 

 ers were supplied with whistles producing the same tone, and 

 sent, one to the westward and one to the eastward. A wind 

 was blowing from the west at the time with a velocity of 

 six and a half miles an hour. The whistle on one steamer 

 was heard until it sailed a mile from the light-ship on which 

 the observers were stationed, while the sound of the other, 

 which was carried by the wind, was heard two and a half 

 miles. This was in accordance with the general experience of 

 the effect of wind in accelerating - the sound-waves. At noon, 

 however, the experiment was repeated in a dead calm, and 

 the same effect was observed, the sound from the steamer that 

 sailed eastward being heard two and a half times as far as 

 the sound from the other steamer. Ao-ain in the afternoon 

 the experiment was tried after the wind had chopped about 

 and was blowing from the east, but the observers were sur- 

 prised to find no change in the result. Apparently the 

 course of the wind had no effect upon the velocity of the 

 sound. Professor Henry was satisfied, however, that the 

 variation in the wind occurred only at the earth's surface, 

 and that a river of wind was flowing steadily from the west 

 all the time. Next day he repeated the experiments under 

 exactly similar conditions, the wind falling to a calm, and 

 then shifting as before. He sent up small balloons at the 

 same time, and found the idea to be correct. A steady cur- 

 rent from the west prevailed all the time. By this beautiful 

 experiment the truth of his theory as to the uniform effect 

 of wind on sound was completely demonstrated. 



Professor Tyndall, in trying to account for the variable 

 rate of the transmission of sound, and the apparently con- 

 tradictory effect at times of the wind's action, refers the 



