298 LETTERS ON NATURAL MAGIC. 



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 soimd, M. 

 Seetzeen 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 produced far exceeded 

 his expectetions, 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 respecting the 

 cause of these sounds. Does the rolling layer of sand, 

 saps 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 neighbouring rocks that 

 of the sounding body? W cannot pretend to answer 

 these questions, but we trust that some philosopher com- 

 petent to the task will have an opportunity of examining 

 these interesting phenomena with more attention, and 

 describing them with greater accuracy. 



The only person, so far as I can learn, who has visited 

 El Nakous since the time of Seetzen is Mr. Gray, of 

 University College, Oxford ; but he has not added much 

 to the information acquired by his predecessor. During 

 the first visit which he made to the place, he heard at the 

 end of a quarter of an hour a low continuous murmuring 

 sound beneath his feet, which gradually changed into 

 pulsations as it became louder, so as to resemble the 

 striking of a clock, and at the end of five minutes it 

 became so strong as to detach the sand. Returning to the 

 spot next day, he heard the sound still louder than before. 



