W. B. Taylor— Recent Researches in Sound. 97 



erable increase of temperature in the lower strata of the air, the 

 lower portion of the sound waves is projected in advance of 

 the upper portion, (p. 71.) Atmospheric vapor also, though 

 exercising but little direct influence on the velocity of sound, 

 " nevertheless plays an important part in the phenomena under 

 consideration ; for it gives to the air a much greater power of 

 radiating and absorbing heat, and thus renders it much more 



susceptible of changes in the action of the sun It is a 



well-known fact that the temperature of the air diminishes as 

 we proceed upward, and that it also contains less vapor. Hence 

 it follows that, as a rule, the waves of sound must travel faster 

 below than they do above, and thus be refracted or turned 

 upward." (p. 72 ) 



The variation of temperature will be greatest in a quiet at- 

 mosphere when the sun is shining. The report of Mr. Glaisher 

 >'0n eight Balloon Ascents in 1862" showed that "The decline 

 of temperature [upward] near the earth with a partially clear 

 sky is nearly double that with a cloudy sky."* " During the 

 night the variations are less than during the day. This reason- 

 ing at once suggested an explanation of the welf-known fact that 

 sounds are less intense during the day than at night. This is a 

 matter of common observation, and has been the subject of 

 scientific enquiry." (p. 73.) The opinion must here be haz- 

 arded that this familiar phenomenon has first received its true 

 and satisfactory explanation from Professor Reynolds. 



Assuming that for a few hundred feet upward, the diminu- 

 tion of temperature on a clear summer day is 1° for each hun- 

 dred feet, a horizontal sound-ray would be bent up in an arc 

 having a radius of about 20 miles. From a clift' 235 feet high, 

 a sound should be audible from 1^ to 2 miles on the sea, and 

 the ray should then begin to rise above the observer's head. 

 This is shown to accord very closely with the observation of 

 Tyndall [6]. Professor Reynolds after quoting the observation 

 at length, remarks : " Here we see that the very conditions 

 which actually diminished the range of the sound were precisely 

 those which would cause the greatest lifting of the waves. 

 And it may be noticed that these facts were observed and re- 

 corded bj Professor Tyndall with his mind altogether unbiased 

 with any thought of establishing this hypothesis. He was look- 

 ing for an explanation in quite another direction. Had it not 

 been so he would probably have ascended the mast and thus 



* Mr. Grlaisher remarks : " Erom these results we may conclude that in a 

 cloudy state of the sky, the decline of temperature is nearly uniform up to the 



decline of 1° in less than 100 feet, gradually decreasing as in the general law- 

 indicated in the preceding section, till it requires 300 feet at the height of 5,000 

 feet, for a change of 1° of temperature." (Rep. Brit. Assoc, 1862, p. 462.) 

 Am. Jour. Sci.— TntRD Series, Vol. XI, No. 63.— Feb., 1876. 



