188 KEPORT— 1871. 



On an Acoustic Phenomenon at Jebel Ncigus, in the Peninsula of Sinai, 

 By Captain H. S. Palmer, B.E. 



Jebel Nagus is the name given to a liigh sand-slope in tlie western coast-range 

 of the peninsula of Sinai, about five miles north of the port of Tor. The sand of 

 this slope possesses the peculiar property of giving forth loud musical sounds when 

 set in motion b}' design or by natural causes. According to a ciuaint native legend, 

 founded on the former monastic occupation of this part of the peninsula, the sounds 

 are said to proceed from the ndgus, or "wooden gong"*, of a monastery buried 

 beneath the sand. Hence the application of the name Nagus to the slope in 

 question. 



The sand-slope is about 200 feet high, and 80 yards wide at its base, narrowing 

 towards the top ; it faces west-south-west. Sandstone cliffs overhang it, and bound 

 it on either side, and an open sandy plain stretches from the foot of the slope to the 

 sea-shore, about three-quarters of a mile distant. The sand of the slope appears to 

 be that from the neighbouring desert plain, derived in the first place from the 

 waste of the sandstone rocks, and then conveyed to its position on the hill-side by 

 the drifting action of high winds ; its grains are large, and consist entirely of 

 quartz. The rock in situ is a soft friable quartzose sandstone, of a pale brown 

 inside, and weathered externally to a dull dark brown. The sand of the slope 

 is so clean, and in its usual condition so extremely dry, and inclined at so steep 

 an angle (about 29^") to the horizon, that it may be easily set in motion by such 

 causes as the passage of men or animals across it, falling debris from the clifls 

 above, or disturbance by the wind. Sometimes also movement on a smaller scale 

 may arise from an abnormal excess of heat and drought, or from the separation 

 of the surface-particles, after their consolidation by rain or dew, on the return of 

 heat and the sun's burning rays. When any considerable quantity of tlie sand is 

 in movement, rolling gradually down over the surface of the slope in thin waves 

 an inch or two deep, just as oil or any thick liquid might roll over an inclined 

 sheet of glass, and in similar festoons or curves, then is heard the singular acoustic 

 phenomenon from which the hill derives its name, at first a deep, swelling, vibratory 

 moan, rising gradually to a dull roar, loud enough, when at its lieight, to be almost 

 startling, and then as gradually dying away, till the sand ceases to roll. Tlie 

 sound is difficult to describe exactly ; it is not metallic, not like that of a bell, nor 

 yet that of a itdf/us. Perhaps the very hoarsest note of an yEolian harp, or tlie 

 sound produced by drawing the finger round the wet rim of a deep-toned finger- 

 glass, most closely resembles it, though there is less music in the sound of the 

 rolling sand : it may .also be likened to the noise produced b^^ air rushing into tlie 

 mouth of an empty metal flask ; sometimes it almost approaches to tlie roar of very 

 distant thunder, and sometimes it resembles the deeper notes of a violoncello, or the 

 hum of a humming-top. The author found by experiment that hot surface-sand was 

 more sonorous than the cooler layers beneath ; it also seemed to run more quickly ; 

 the first experiments on any one part of the slope produced louder effects than 

 subsequent ones. Surface-sand, at a temperature of 103° Falir., exposed to tlie 

 sun's full glare, produced the grandest effect observed, while sand in shade, at G2^, 

 was almost mute. By day the heat on the slide is generally very great. Move- 

 ment of the sand when moist is not accompanied by unusual sounds. Excavation 

 was impossible, on account of the continuous flow of the sand when disturbed ; in 

 some places nothing solid could be reached by probing; in others, rock was felt a 

 few inches below the surface, but whether (';; situ or not could not be ascertained. 

 When sand is rolling down and producing sound, there is a distinct vibration on 

 the slide, increasing with the intensity of the sounds. Throughout Capt. Palmer's 

 stay, the wind blew from N.W. ; the effects produced on the slide by winds from 

 other quarters have yet to be observed. Experiments on two other sand-slides, a 

 little to the south of Jebel Nagiis, and resembling it in many particulars, did not 



Jebel Nagiis had been several times visited and described, but the author had 

 * Used in place of bells in convents of the Greek Church. 



