2i2 



SIXTH REPORT — 1836. 



1086*7 feet. This must be considered as applying to the mean 

 state of the hygrometer, the nature of which not being stated, 

 its indications could not be made use of. 



Experiments were made by Captain Parry and Lieut. Foster 

 expressly to determine the effect of low temperatures on the 

 velocity of sound*. The following is a mean of results. 



A comparison of the velocities at the highest and lowest tem- 

 peratures differing by 74°'6, gives an increase of velocity of 

 1*126 feet for each increase of temperature by 1° of Fahren- 

 heit. A like comparison of the velocity at the lowest tem- 

 perature, — 41°*3, mth the velocity in Mr. Goldingham's 

 experiments at the temperature 87°, gives an increase of 1*35 

 feet for each degree of Fahrenheit. 



The experiments of Captain Parry and Lieut. Foster at Port 

 Bowen in 1824 — 1825 have been compared with the theory by 

 Professor MoUf. On using the coefficient 1*375, the velocity 

 given by the theory falls short of the experimental value by 

 17"47 feet, a difference exceeding that resulting from a like 

 comparison of the experiments in the Netherlands by something 

 less than 2^ feet. In the arctic experiments the state of moi- 

 sture in the air was not noted; but Professor Moll shows that 

 this omission is productive of a very small error in very low 

 temperatures. The near agreement of experiments made under 

 circumstances so widely different, must lead us to suspect, as 

 Professor Moll justly observes, that the difference which still 

 remains between the results of computation and observation are 

 to be ascribed to some imperfection in the theoretical formula, 

 and not to any fault in the observations;}:. 



In 1828 M. Dulong§ read a memoir on the specific heats of 

 elastic fluids, which requires to be noticed in conjunction with 



* See p. 235 of the Supplement to the Appendix of Captain Parry's Voyage 

 in 1819—1820. 



+ Phil. Trans. 1823, p. 97. 



X For a synoptical view of the results obtained by different observers, the dates 

 of their observations, and the circumstances under which they were made, I 

 may refer to a table in Art. 16 of Sir John Herschel's Treatise on Sound in 

 the Encyclopesdia Metropolitana. 



§ Memoires de I'Institut, torn. x. p. 147. 



