Curiosities of Science. 27 



Sountr ant ILtgfjt 



SOUNDING SAND. 



MR. HUGH MILLER, the geologist, when in the island of Eigg, 

 in the Hebrides, observed that a musical sound was produced 

 when he walked over the white dry sand of the beach. At each 

 step the sand was driven from his footprint, and the noise was 

 simultaneous with the scattering of the sand ; the cause being 

 either the accumulated vibrations of the air when struck by 

 the driven sand, or the accumulated sounds occasioned by the 

 mutual impact of the particles of sand against each other. If 

 a musket-ball passing through the air emits a whistling note, 

 each individual particle of sand must do the same, however 

 faint be the note which it yields ; and the accumulation of 

 these infinitesimal vibrations must constitute an audible sound, 

 varying with the number and velocity of the moving particles. 

 In like manner, if two plates of silex or quartz, which are but 

 crystals of sand, give out a musical sound when mutually 

 struck, the impact or collision of two minute crystals or par- 

 ticles of sand must do the same, in however inferior a degree ; 

 and the union of all these sounds, though singly imperceptible, 

 may constitute the musical notes of " the Mountain of the 

 Bell" in Arabia Petraea, or the lesser sounds of the trodden 

 sea-beach of Eigg. North-British Review, No. 5. 



INTENSITY OF SOUND IN RAREFIED AIR. 



The experiences during ascents of the highest mountains 

 are contradictory. Saussure describes the sounds on the top 

 of Mont Blanc as remarkably weak : a pistol-shot made no 

 more noise than an ordinary Chinese cracker, and the popping 

 of a bottle of champagne was scarcely audible. Yet Martius, 

 in the same situation, was able to distinguish the voices of the 

 guides at a distance of 1340 feet, and to hear the tapping of a 

 lead pencil upon a metallic surface at a distance of from 75 to 

 100 feet. 



MM Wertheim and Breguet have propagated sound over 

 the wire of an electric telegraph at the rate of 11,454 feet per 

 second. 



DISTANCE AT WHICH THE HUMAN VOICE MAY BE HEARD. 



Experience shows that the human voice, under favourable 

 circumstances, is capable of filling a larger space than was ever 



