ON THE MATHEMATICAL THEORY OF FLUIDS. 



211 



cities of sound when aided, and when opposed by the wind. 

 The experiments were made with intervals between the stations, 

 varying from less than half a mile to 2^ miles, and in tempera- 

 tures varying from 27° to 66° Fahr. The mean of eight results 

 reduced to the temperature of freezing is stated by Sir John 

 Herschel (Art. Sound, Encij. Metro]}.) to be 1088-05 feet. The 

 velocity observed at the temperature of freezing was 1090' 17 

 feet. 



A valuable series of experiments was made byMr.Goldingham, 

 at Madras, in 1820, extending through every month of the year. 

 The following is a table of the mean temperature and mean de- 

 termination of velocity for each month. 



It is interesting to observe, as the author remarks, " how re- 

 gularly the mean velocity proceeds to a maximum about the 

 middle of the year, and afterwards retraces its steps, giving us 

 a velocity in one case of 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." In 

 these experiments (which have been compared with theory by 

 Mr. Galbraith*) the indications of the barometer and hygro- 

 meter were noted ; and though the experiments were not made 

 by simultaneous reports, the effect of the wind may be consi- 

 dered to be completely eliminated in the mean of the observa- 

 tions of the whole year. It is worthy of remark that the differ- 

 ence between the greatest and least velocities is much more 

 considerable than, according to theory, would be due to the 

 corresponding difference of temperature. The greatest and least 

 indications of the hygrometer were 27*85 and 1*43, the former in 

 July and the other in December, the two months in which the ve- 

 locity of sound was greatest and least. Sir John Herschel gives 

 as the mean determination from the total of Mr. Goldingham's 

 experiments reduced to the temperature of freezing, a velocity of 



• See Phil. Mag. vol. Ixvi. p. 109, and vol. Ixviii. p. 214. 

 VOL. V. — 1836. R 



