Velocity of Sound. 413 



poses that of the sound, the difference of the separate velocities 

 must be taken. 



6th, That in the case of echoes, the velocity of the refected 

 sound, is the same as that of the direct sound. 



7th, That, therefore, distances may frequently be measured 

 by means of echoes. 



8 th, That an augmentation of temperature occasions an 

 augmentation of the velocity of sound ; and vice versa. — (See 

 Newton, Principia, lib. 2. prop. 50. Parkinson's Mechanics, 

 vol. ii. p. 148.) 



The inquiries with regard to the transmission of sound in 

 the atmosphere*, which, notwithstanding the curious investi- 

 gations of Newton, Laplace, Poisson, and others, require the 

 further aid of experiment for satisfactory determination, are, 

 I think, the following; viz. 



1st, Whether hygrometric changes in the atmosphere have 

 much or little influence on the velocity of sound? 



2d, Whether barometric changes in the atmosphere have 

 much or little influence? 



3d, Whether, as Muschenbroek conjectured, sound have 

 not different degrees of velocity, at the same temperature, in 

 different regions of the earth ? And whether high barometric 

 pressures would not be found (even independently of tempera- 

 ture) to produce greater velocities? 



4th, Whether, therefore, sound would not pass more slowly 

 between the summits of two mountains, than between their 

 bases ? 



5th, Whether sound, independently of the changes in the 

 air's elasticity, move quicker or slower near the earth's sur- 

 face, than at some distance from it? — (See Savart's interesting 

 papers on the communication of sonorous vibration.) 



6th, Whether sound would not employ a longer interval 

 in passing over a given space, as a mile, vertically upwards, 

 than in a horizontal direction? and, if so, would the formulae 

 which should express the relation of the intervals include 

 more than thermometric and barometric coefficients? 



7th, Whether or not, the principle of the parallelogram of 

 forces may be employed in estimating the effect of wind upon 

 sound, when their respective velocities do not aid, or oppose 

 each other in the same line, or nearly so? 



8th, Whether those eudiometric qualities, generally (whether 

 hitherto detected or not) which affect the elasticity of the air, 



* I say nothing in this paper of the transmission of sound through the 

 gases, along metallic conductors, &c. These furnish a most interesting de» 

 partment of separate inquiry. 



will 



