72 Mr Ch. Martins on the Intensity of Sound 



produced 2117 metres lower. To equalize the two sounds, it 

 was necessary to charge the lower mortar with 75 grammes 

 of powder, and the upper one with 90 grammes. 



The accounts of the ascents of the highest mountains 

 contain some observations upon the weakening of the sound, 

 but they often contradict each other. On the top of Mont 

 Blanc, at 4810 metres above the sea, the sounds, according 

 to Saussure, were remarkably weak. A pistol shot made no 

 more noise than a china-cracker does in a room.* Mr 

 Auldjo, being upon the same summit, cut the string retain- 

 ing the cork of a bottle of champagne ; the cork was pro- 

 jected to a distance, but the noise was scarcely sensible : he 

 adds, that the sounds of voices seemed to him weakened. Mr 

 Fellows, who made the ascent of Mont Blanc in the same 

 year, is still more explicit : he says, that having desired the 

 guides who accompanied him to sing the ranz des Faches, 

 they could never succeed, because they could not hear each 

 other. t This assertion is evidently exaggerated. Placed 

 on the summit of Mont Blanc, M. Bravais, M. Lepileur, and 

 I, heard very distinctly the guides speaking to each other 

 near the rock la Tourette, distant about 400 metres from the 

 top, and reciprocally our guides also heard our voices when 

 we conversed together. At fifteen or twenty paces, M. 

 Lepileur remarked the noise I made when tapping with a 

 lead pencil upon the metallic slider of my barometer. J 



Desiring to acquire some ideas more positive upon this 

 subject, I sought the means of obtaining a continuous sound 

 of a constant intensity, and producible at will : this I found 

 in one of M. Marloye's diapasons, mounted upon a hollow 

 box of very dry deal, parallelopipedal in form and 0"^ 305™™ 

 long, by 0™ 065™™ broad. The box was closed on one side 

 and open on the other ; the diapason sounded ut^^ which has 

 512 vibrations in a second. In a state of repose the separa- 



* Voyages dam les Alps, p. 220. 



t Key, Influence sur le corps humain des ascensions sur les hautes montagnes 

 {Revue Medicate, 1842, t. iv. p. 343.) 



X Lepileur, M^moire sur les ph^nomenes physiologiques qu'on observe en 

 s'elevant sur les hautes montagnes {Revue Medicate 1846.) 



