Mechanical Bdmce, 8^. 163 



iii. Nor consequently does a difference in the instrument from 

 which the sound is emitted. 



iv. That wind greatly affects sound in poiot of in^ensiVy, and that 

 it affects it also in point of velocity. 



V. That when the direction of the wind concurs with that of the 

 sound, the sum of their separate velocities gives the apparent velocity 

 of sound : when the direction of the wind opposes that of the sound 

 the difference of the separate velocities must be taken. 



vi. That in the case of echoes the velocity of the reflected sound 

 is the same as that of the direct sound. 



vii. That therefore distances may frequently be measured by 

 means of echoes. 



viii. That an augmentation of temperature occasions an angmen- 

 tation of velocity of sound, and viceversd. 



The inquiries with regard to the transmission of sound in the 

 atmosphere, which, notwithstanding the curious investigations ef 

 Newton, Laplace, Poisson, and others, require the further aid of 

 experiment for satisfactory determination are, I think, the following, 

 viz., 



i. Whether hygrometrie changes in the atmosphere have much 

 or little influence on the velocity of sound. 



ii. Whether barometric changes in the atmosphere have much or 

 little influence. 



iii. Whether, as Muschenbroek conjectured, sound have not differ- 

 ent degrees of velocity, at the same temperature, in different re- 

 gions of the earth ? And whether high barometric pressure would 

 not be found (even independently of temperature) to produce greater 

 velocities? 



iv. Whether, therefore, sound would not pass more slowly between 

 the summits of two mountains than between the bases? 



V. Whether sound, independently of the changes in the air's 

 elasticity, move quicker or slower near the earth's surface than at 

 some distance from it? (See Savart's interesting papers on the com- 

 munication of Sonorous Vibration.) 



' vi. 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 ba- 

 rometric coefficients ? 



vii. Whether or not the principal 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 ? 



viii. Whether those eudiometric qualities generally (whether 

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

 not proportionally affect the velocity of sound? and if so, how 

 are the modifications to be appreciated? 

 M2 



