242 LETTERS ON NATURAL MAGIC. 



culty as far as the sandy declivity, a height of 

 seventy or eighty feet, and had rested beneath 

 the rocks where the pilgrims are accustomed to 

 listen to the sounds. 



While in the act of climbing, M. Seetzen heard 

 the sound from beneath his knees, and hence he 

 was led to think that the sliding of the sand was 

 the cause of the sound, and not the effect of the 

 vibration which it occasioned. At three o'clock 

 the sound became louder and continued six 

 minutes, and after having ceased for ten minutes, 

 it was again heard. The sound appeared to have 

 the greatest resemblance to that of the humming- 

 top, rising and falling like that of an ^Eolian 

 harp. Believing that he had discovered the true 

 origin of the sound, M. Seetzen was anxious to 

 repeat the experiment, and with this view he 

 climbed with the utmost difficulty to the highest 

 rocks, and sliding down as fast as he could, he 

 endeavoured, with the help of his hands and feet, 

 to set the sand in motion. The effect thus pro- 

 duced far exceeded his expectations, and the sand 

 in rolling beneath him made so loud a noise, that 

 the earth seemed to tremble to such a degree 

 that he states he should certainly have been 

 afraid if he had been ignorant of the cause. 



M. Seetzen throws out some conjectures re- 

 specting the cause of these sounds. Does the 

 rolling layer of sand, says he, act like the fiddle- 

 bow, which, on being rubbed upon a plate of glass, 

 raises and distributes into regular figures the 

 sand with which the plate is covered ? Does the 

 adherent and fixed layer of sand perform here 

 the part of the plate of glass, and the neighbour- 

 ing rocks that of the sounding body ? We can- 



