208 Afr. Ooldingham on the Velocity of Sound. [Sept. 



Now, by numerous combinations of the observations just 

 given, when the air was cahn, we are led to conclude : first, 

 that for each degree of the thermometer 1*2 feet may be allowed 

 in the velocity of sound for a second ; for each degree of the 

 hygrometer 1*4; and for one tenth of an inch of the barometer* 

 9*2 feet. Then taking these numbers as the basis of the compa- 

 rison, we find the mean difference of the velocity between a 

 calm, and in a moderate breeze of wind, to be nearly 10 feet in 

 a second. And by comparing other results together, a difference 

 of about 21-^ feet in a second, or 1275 in a minute is found 

 between, the wind being in the direction of the motion of sound, 

 or opposed to it. 



Before I conclude these introductory observations, and expla- 

 nations of the experiments, it may be proper to refer more parti- 

 cularly to Table XI. containing the mean motion of sound for 

 each month of the year, by the experiments with the Mount 

 gun, according to the state of the atmosphere indicated by the 

 different instruments ; and to the prevailing monsoons, which 

 may be considered to be the same, during the same months, 

 every year ; full information respecting which is given in the 

 former Tables. On examining this Table, it is rather curious to 

 observe how regularly the mean Telocity proceeds to a maximum 

 about the middle of the year, and afterwards retraces its steps ; 

 giving us a velocity in one case 1164 feet in a second, and in the 

 other of only 1099 feet. This regularity would, no doubt, be still 

 greater with the mean of the observations of several years. 



Table XL 



Mean Motion of Sound for each Month, according to the Expe- 

 riments with the Mount Gun, 



• The rise and fall of the barometer is very limited in this country, a.s will be seen by 

 an examination of the Tables. A huddcn Ml of 0-3 inch indicates a gale of wind. 



