PHILOSOPHICAL SOCIETY OF WASHINGTON. 39 



With regard to fog, Mr. Taylor said, we are not to conceive the 

 sound vibrations as passing alternately through air and water, (as 

 a ray of light does,) but taking into view the average wave-length 

 of sound (several feet ordinarily) and the enormous number of 

 water particles contained in that space, we must contemplate the 

 whole mass as a homogeneous medium taking up the sound waves 

 in the same manner, whether the air were perfectly dry, or were 

 precipitating excessive moisture in the form of rain. In the absence 

 of sensible wind, the air thus supersaturated with moisture would 

 be practically very homogeneous, and thus generally well adapted 

 to the normal transmission of sound. 



A similar remark applies to falling snow, (when not accompanied 

 with strong wind,) with the additional circumstance that, while the 

 precipitation and congelation would tend to warm the upper regions 

 of the air, any melting of the snow as it fell would cool the lower 

 region. This condition of relative warmth above and cold below 

 is favorable to the conveyance of sound to a distance — as first 

 pointed out by Prof. Osborn Reynolds, of Manchester, — by reason 

 of the expanding spherical wave-front being slightly more accele- 

 rated above than below, (in accordance with well known principles,) 

 and thus causing the horizontal or slightly rising sheets of sound 

 to be dished downward. 



The next communication was by Mr. William Harkness on 

 the relative accuracy of different methods of determining the solar 

 parallax. 



This paper is published in full in the American Journal of 

 Science for November, 1881, No. 131, vol. 22, pp. 375-394. 



205th Meeting. November 5, 1881. 



The President in the Chair. 

 Forty-three members present. 

 Mr. J. C. Welling presented the following communication on 



ANOMALIES OP SOUND SIGNALS. 



In the year 1865 Prof. Henry, while making some observations 

 on the intensity of sounds, discovered that a sound moving against 

 the wind, and which was inaudible to the ear of an observer on the 



