in the Barified Air of High Mountains. 71 



this time, however, no rigorous attempt had been made to 

 estimate this variation, w^hich already complicated the first 

 experiments made on the velocity of sound. When Lacaille, 

 Maraldi, and Cassini de Thury, attempted to measure the 

 velocity of sound, the last, placed at the station of Dammar- 

 tin, heard very well for several days an eight-pounder fired 

 from the top of Montmartre, the distance being 31,337 

 metres.* At Cayenne, La Condamine heard the report of 

 a twelve-pounder placed 39,430 metres off.t On the other 

 hand, Godin and Georges Juan, co-labourers with La Conda- 

 mine, did not hear a nine-'pounder at a distance of 37,031 

 metres ;J the two stations being above the plain of Quito, the 

 one Gonapoli, 4110 metres, the other Pamba-Marca, 3009 

 metres above the level of the sea.§ The experiment was re- 

 peated upon the plain of Quito at an altitude of 2900 metres ; 

 the same cannon, placed at a distance of 20,500 metres, was 

 heard, though very faintly. || So that, upon the plain of 

 Quito, the explosion of a nine-pounder appeared weaker at a 

 distance of 20,500 metres than that of an eight-pounder 

 31,300 metres off, in the environs of Paris. 



The intensity of the sound depends on the density of the 

 air at the place of primitive disturbance, and not on that of 

 the strata traversed by it, nor on that of the air surrounding 

 the hearer.lF The following trials furnish a proof of this. 

 When M. Bravais and I made our experiments upon the ve- 

 locity of sound ascending and descending, between Brienz 

 and the summit of the Faulhorn, we employed two mortars 

 of exactly the same fount.** In the first experiments we 

 gave them the same charge, but the sound created in the air, 

 at an altitude of 2682 metres, was much weaker than that 



with a repetition of the same in the open field. — Philosophical Transactions, 

 vol. xxiv. p. 1902. 



* Memoires de V Academic des Sciences, ann6e 1738, p. 128. 



t Relation ahregee d\m voyage fait dans Vinterieur de VAmeriqtte. (Memoires 

 de r Academic des Sciences, ann6e 1745, p. 488.) 



X Journal du Voyage, fait par ordre du Roi d Vequateur, t. i. p. 36. 



§ Be la figure de la Terre, par Bouguer, p. 124. 



II Journal du Voyage, &c., t. i. p. 98. 



% Poisson. Traite de Mecanique, t. ii. p. 706. 

 ** Annales de Chimie et de Physique, 3« serie, t. xiii. p. 1 ; 1845. 



