64 THE CRUISE OF THE BETSEY ; OR, 



municate to the atmosphere those vibratory undulations that 

 are the producing causes of sound : the grains, even when 

 sonorous individually, seem, from their inevitable contact 

 with each other, to exist under the influence of that simple 

 law in acoustics which arrests the tones of the ringing glass 

 or struck bell, immediately as they are but touched by some 

 foreign body, such as the hand or finger. The one grain, 

 ever in contact with several other grains, is a glass or bell on 

 which the hand always rest. And the difficulty has been felt 

 and acknowledged. Sir John Herschel, in referring to the 

 phenomenon of the Jabel Nakous, in his " Treatise on Sound," 

 in the " Encyclopaedia Metropolitana," describes it as to him 

 " utterly inexplicable /' and Sir David Brewster, whom I had 

 the pleasure of meeting in December last, assured me it was 

 not less a puzzle to him than to Sir John. An eastern tra- 

 veller, who attributes its production to " a reduplication of 

 impulse setting air in vibration in a focus of echo," means, I 

 suppose, saying nearly the same thing as the two philosophers, 

 and merely conveys his meaning in a less simple style. 



I have not yet procured what I expect to procure soon, 

 sand enough from the musical bay at Laig to enable me to 

 make its sonorous qualities the subject of experiment at home. 

 It seems doubtful whether a small quantity set in motion on 

 an artificial slope will serve to evolve the phenomena which 

 have rendered the Mountain of the Bell so famous. Lieu- 

 tenant Welsted informs us, that when his Bedouin first set 

 the sand in motion, there was scarce any perceptible sound 

 heard ; it was rolling downwards for many yards around 

 him to the depth of a foot, ere the music arose ; and it is 

 questionable whether the effect could be elicited with some 

 fifty or sixty pounds weight of the sand of Eigg, on a slope 

 of but at most a few feet, which it took many hundredweight 

 of the sand of Jabel Nakous, and a slope of many yards, to 

 produce. But in the stillness of a close room, it is just pos- 



