224 Mr. Wheatstone on the 



Other experiments of a similar nature were subsequently made 

 by Herhold and Rafn*, Hassenfratz and Gay Lussacf 

 &c. ; but the first direct observations of the actual velocity of 

 sound through solid conductors were made by Biot, assisted at 

 different times by Bouvard and Martin. These experiments 

 were made on the sides of the iron conduit-pipes of Paris, 

 through the length of 951m. 25 ; and the mean result of two 

 observations made in different ways gave 3459 metres, or 

 11,090 feet per second, for the velocity of sound in cast 

 iron J. 



Previously to these last-mentioned experiments, Chladni 

 had, in an ingenious manner, inferred the velocity of sound in 

 different solid substances ; and his results are fully confirmed 

 by calculations from other grounds. His method was founded 

 on Newton's demonstration, that sound travels through a space 

 of a given length, filled with air, in the same time that a 

 column of air of the same length, contained in a tube open at 

 both ends, makes a single vibration ||. His own discovery 

 of the longitudinal vibrations of solid bodies, which are exactly 

 analogous to the ordinary vibrations of columns of air, enabled 

 him to apply this proposition to solid bodies, and to establish 

 the general law, that sound is propagated through any elastic 

 substance in the same time in which this substance makes one 

 longitudinal vibration. In this manner he ascertained the 

 velocities of sound in the following substances, among others : 

 tin 7,800, silver 9,300, copper 12,500, glass and iron 17,500, 

 and various woods from 11,000 to 18,000 feet in a second. 



From the experiments of M. Perolle , it would appear 

 that the intensity with which sound is communicated through 

 solid matters is nearly in proportion to the velocity of its trans- 

 mission. 



* Reil's Archiv fur die Physiologic, vol. iii., No. iii., p. 178. 



f Annales de Chimie, tome liii., p. 64. 



J Memoires de la Societe d'Arcueil, tome ii., p. 403. 



|| A single vibration is here considered as the motion of the vibrating body 

 between the two opposite limits of its excursion, and with this signification the ex- 

 pression is adopted by Chladni. Other authors, however, regard this, with Newton 

 and Sauveur, as a semi-vibration, and call an entire vibration the motion of the 

 vibrating body from one limit of its excursion until it again arrives at the same 

 limit. This difference of meaning attached to the same term has given rise to 

 several mistakes. 



Journal de Physique, tome xlix., p. 382. 



