167 



PLYMOUTH INSTITUTION. 

 PROCEEDINGS IN THE ATHENAEUM. 



FEBRUARY 13th. Dr. BUND'S Lecture on Sound. 



Having detailed the importance of Acoustics, defined and adduced 

 several instances of the modification of sound by attenuated and 

 dense air ; the Lecturer stated, as the fundamental proposition of 

 Acoustics, that Sound requires some ponderable medium for its pro- 

 pagation, and that in air the intensity of sound increases with the 

 density of the air; he also observed that the next definition is as 

 equally important, viz. that the motion which produces sound is al- 

 ways a motion of vibration such as is perceptible in the chords of a 

 violin, or such as a mass of air is made to exert in the hollow of a 

 flute. 



The Lecturer then proceeded to show that the principle of vibra- 

 tion which was evidently true in its generality, when applied to the 

 sonorous body itself, was equally true when applied to the air, or the 

 medium that surrounds the sonorous body, and that receives the sound 

 to transmit it to in definite distances ; and having explained this ela- 

 borately and at length he noticed the velocity of sound, and observed 

 that it was affected by the velocity and direction of the wind as well as 

 by temperature : from some experiments instituted by the Academy 

 of Paris the velocity of sound was found to be 1090 feet in a second, 

 and from Mathematical calculations made by Sir I. New T ton it was 

 found to be 916 feet in a second, the discrepancy of these results was 

 accounted for by La Place who discovered that the velocity of sound 

 is greater in warm air than in cold. M. Biot proved, by experiments 

 with a tube 300 feet long, that all sounds, whatever be their tone and 

 intensity, travel with the same velocity ; and he further found, that 

 when sound is prevented from losing itself in the air, it may be con- 

 veyed to great distances : the lowest whisper made at one end of his 

 tube was distinctly audible at the other, and the transmission of every 

 agitation of the air was so faithful, that a pistol fired at one extremi- 

 ty blew out a candle at the other. 



Rain, fogs, snow, &c., which have no influence on the velocity of 

 sound diminish its intensity very much, and it is propagated with 

 much force and clearness over tranquil water and ice. 



The Lecturer next spoke of reflected sound. When sound in the 

 course of its propagation meets with an obstacle of sufficient extent 

 and regularity, it is reflected and produces an echo : the reflected 

 sound may be again reflected, by another obstacle, and thus the echo 



