C. GENERAL PHYSICS. 187 



phenomena to a flocculent condition of the atmosphere, pro- 

 duced by the mingling of air and vapor, and by patches of 

 air of different temperature. Professor Henry said that fog 

 has been shown to have no apparent effect on the penetrating 

 power of sound. A sound has been heard twenty-five miles 

 through a dense fog. Snow-storms have no effect. Vapor 

 in the air could not, therefore, produce the phenomena, as 

 Tyndall supposes. The fault with Tyndall's experiments 

 were that they were all made in one direction, and from 

 these partial experiments he derived his theory of the acous- 

 tic opacity of the atmosphere. Last summer Professor Henry 

 placed a large steam-trumpet on a steamer. The wind was 

 from the west, and the trumpet was pointed northward. The 

 steamer sailed toward the wind, and carried the sound only 

 three and a half miles, but in sailing in a contrary direction the 

 sound was heard for a distance of eiii'ht miles. If Professor 

 Tyndall had observed the sound from one direction only, he 

 would have called the day opaque ; if from the other only, he 

 would have concluded it was quite clear. JV. IT. Tribune. 



ON THE REFRACTION OF SOUND BY THE ATMOSPHERE. 



The above is the title of a very interesting paper, read be- 

 fore the Royal Society April 23, 1874, by Professor Osborne 

 Reynolds. The principal object of this paper is to show 

 that sound is refracted upward in the atmosphere in direct 

 proportion to the upward diminution of the temperature, and 

 hence to explain several phenomena of sound, and particular- 

 ly the results of Professor Tyndall's recent observations off 

 the South Foreland. 



The paper commences by describing the explanation of the 

 effect of wind upon sound, viz., that this effect is due to the 

 lifting of the sound from the ground, and not to its destruc- 

 tion, as is generally supposed. The lifting of the sound is 

 shown to be due to the different velocities with which the 

 air moves at the ground and at an elevation above'it. Dur- 

 ing a wind the air moves faster above than below, therefore 

 sound moving against the wind moves faster below than 

 above, the effect of which is to refract or turn the sound 

 upward ; so that the " rays" of sound, which would otherwise 

 move horizontally along the ground, actually move upward 

 in circular or more nearly hyperbolic paths, and thus, if there 



