NATURAL PniLOSOPnT. 179 



He finds also that the diminution of the velocity of sound in tubes 

 full of air increases with the len^^th of the wave of sound. He 

 further has established that fine powder (as the extremely light 

 powder from dried gelatinous silica), in the interior of a large 

 tube, had no effect on the velocity of transmission, while in tubes 

 of small diameter the velocity decreased in proportion to the 

 quantity and lightness of the powder. He finds, finall}', that the 

 velocity of propagation in a tube is not influenced by the intensity 

 of the sound, nor by the roughness or smoothness of the interior. 



NEW FACTS IN ACOUSTICS. 



M. Regnault, of the Institute of France, has been making use 

 of the new sewers of Paris for the purpose of testing, on a large 

 scale, some of the questions in acoustics concerning which there 

 has been much doubt. By firing a pistol in tubes and sewers of 

 various diameters, he found that the sound was carried to the fol- 

 lowing distances : 1,282 yards in a passage of 4.2 inches diameter ; 

 4,191 yards in a passage of 11.8 inches diameter; 10,494 yards in 

 a passage of 43 inches diameter. The nature of the materials 

 and the construction of such passages exercise great influence on 

 the rapidity with which sound is transmitted. In the large Paris 

 sewers, trumpets are used to convey orders to the workmen, and 

 it is found that in those passages whose sides are cemented, the 

 sound is convej'ed to a much longer distance than in others whose 

 sides are left as first constructed, with the rough stones only. It 

 is one of the primary principles laid down in text-books, that the 

 velocity of the vibrations of sonorous bodies in the same medium 

 is the same for all sounds, grave or sharp, strong or feeble, and 

 whatever may be their pitch ; but the researches of M. Regnault 

 would seem to show that this generally received belief is not 

 correct. He asserts that sounds of different pitch are not prop- 

 agated with equal rapidity but separate from each other on the 

 way. 



Acute sounds, also, travel with less swiftness than grave ones : 

 thus, when a barytone sang in very long sewers, and at the en- 

 trance of water conduits, the key-notes were heard at a distance 

 before the harmonics which succeeded it and one another, accord- 

 ing to the degree of their altitude. The propagation of sound 

 consequently disarranges the harmonics of which it is composed ; 

 thus an air, eml^racing a certain extent of the gamut, if heard at 

 a lung distance, would be seriously altered. This decomposition 

 in tubes may be on account of the friction caused by the sides of 

 the tube or passage-way, and cannot be noticed in the open air. 

 The facts propounded by M. Regnault will cause the philosophers 

 to renew their investigations with renewed interest. — Scientific 

 American. 





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