A yet unsolved riddle of Nature.
HE two explorers, Mr. Bertram Thomas and Mr. H. St. John Philby, the only white men ever to have crossed the Great Desert of the so-called “Empty Quarter” of Arabia, both describe how they were startled by the phenomenon known as “singing sands,” the exact causes of which have long been debated by scientists.
Mr. Thomas and his party were in the heart of the vast desert, floundering along through heavy sand dunes, when the intense silence was suddenly broken by a loud droning of a musical note. One of his Badu companions pointed to a steep sand cliff about 100 feet high and shouted, “Listen to that ridge of sand bellowing!”
All the explorer could see was a filmy wisp of sand being carried up the gentle windward slope to spill like smoke over its top. On another occasion, Mr. Thomas was similarly startled by a curious note emitted from the sand as his camel trod on it, but the tribesman at his side, a Murri who was quite familiar with the phenomenon, could only give as an explanation some dark activity in the uppermost of the seven underworlds. The Arabs, as a matter of fact, attributed the sounds to the spirits of the sand dunes talking.
In Mr. Thomas’ case, the note continued for about two minutes, ceasing as abruptly as it had begun. When Mr. St. John Philby experienced a similar thing a few months later, it was set up artificially, although accidentally. He, too, was in the heart of the Empty Quarter, and he heard the noise in the afternoon, at about the same time as Mr. Thomas had heard it. The explorer was resting in his tent when his attention was arrested by a deep, musical, booming sound. Looking out, he discovered that it had been set up by one of the party walking up the steep sand slope of the dune encircling the camp.
The traveler’s own description of what he heard and saw is worth quoting: “Quite suddenly the great amphitheatre began to boom and drone with a sound not unlike that of a siren or perhaps an aeroplane engine—quite a musical, pleasing, rhythmic sound of astonishing depth . . . . The conditions were ideal for the study of the sand concert, and the first item was sufficiently prolonged—it lasted perhaps about four minutes—for me to recover from my surprise and take in every detail. The men working at the well started a rival and less musical concert of ribaldry directed at the Jinns [desert spirits] who were supposed to be responsible for the occurrence. . . . I realized that the key to the situation was Sa’dan, seated on the top of the slope. It was evident that the music was being engendered by the sand sliding down the steep slope from under him.”
Mr. Philby followed Sa’dan’s example and found that he, too, was able to produce the same sound by setting masses of sand in motion down the side. The noise commenced with a grating sound and was gradually increased into a musical booming, which just as gradually decreased until it died away. He experimented by pushing a bottle into the singing sand, and as he withdrew it there followed a wail like that of a trombone. At another time he plunged into the moving mass of sand halfway down the slope, and it appeared to throb beneath him like a great organ.
These singing sands of southern Arabia have only become known to science this century, but it has been truly said that there is nothing new under the sun. The phenomenon was known to the Chinese at least a thousand years ago. One of their writers left an account of an area in the province of Kansu where it had been noted in the ninth century. The document speaks of the “Hill of Sounding Sand,” which was 500 feet high in places. According to the author it possessed strange, supernatural qualities: “Its peaks taper up to a point, and between them there is a mysterious hole which the sand has not been able to cover up.” The writer said that in the height of summer this hill of sand gave out sounds of itself, but if trodden by men or horses, the notes could be heard for long distances. The manuscript also spoke of a queer custom which was followed at the time to induce the singing. The account runs, “It is customary on the tuanwu day (the Dragon Festival on the fifth of the fifth moon) for men and women from the city to clamber up to some of the highest points and rush down again in a body, which causes the sand to give forth a rumbling noise like thunder. Yet when you come to look at it the next morning the hill is found to be just as steep as before. The ancients called this the Hill of Sounding Sand; they deified the sand and worshiped it there.”
The Misses French and Cable, well-known missionaries in inland China, have also recorded their observations of the phenomenon in Chinese Turkestan. The City of Sands (Tunhwang) takes its name from the ranges of sand dunes that lie to the south, stretching out into the great desert of Lob. These sand hills possess the property of “singing” when the sand is moved. Before the desert gale blows, a sound like the rattle of drums is heard, but at any time the hills can be induced to voice their curious song by those who will pay the price of climbing their steep slopes. Visitors do this and then slide down the sharp incline from the knifelike edge of the highest point for the sheer fun of hearing the great vibration, which seems to spring from the very center of the mighty hill of loose sand.
Tschiffely, the “Iron Swiss,” hero of the famous horseback ride from Buenos Aires to Washington, records a strange experience he had on the Peruvian coast, and one wonders whether this, too, was allied with the phenomenon of singing sands . He fell asleep one night on a sand hill but was awakened several times by a strange noise like the beating of drums or like a motor launch traveling on a river. As he could see nothing, he went to sleep again and only awoke when the sun was hot. Then he noticed that he had been sleeping near a “gentilar,” as the ancient Indian burial grounds are called.
The next day the natives asked him if he had heard the manchang. As this sounded rather like Chinese to Tschiffely, he asked them what it meant. They explained that the sand hill where he had slept was haunted and that every night the dead Indians of the “gentilar” danced to the beating of drums. In fact, they told him so many blood-curdling stories about the hill that he began to consider himself lucky to be alive.
When later he spoke with an educated gentleman, the latter told him that both Baron von Humboldt and Raimondi, who had once investigated the strange phenomenon of that hill, had expressed the opinion that the peculiar sounds so frequently heard during the night were due to underground waters that moved as the temperature changed. Another theory put forward is that sea breezes blowing from a certain direction hit the sandy ripples on the slopes of the hill to produce this strange sound.
It is to the deserts that one must turn to hear the finest exhibitions produced by singing sands, because the immeasurable quantities of sand which characterize them offer ample opportunities for the production of the sounds. But it should be noted that a similar phenomenon has been reported from beach sands. The little island of Eigg, in the Scottish Hebrides, for instance, is a spot unique along Scotland’s western shores, for in the Bay of Laig are found sands that sing.
The honor of the first discovery of similar sands in England appears to go to Mr. C. Carus-Wilson, who found them about 60 years ago at Studland Bay, on the coast of Dorset. They have also been recorded on the coast of North Wales; and in the United States two observers have reported them at 74 places on the Atlantic coast alone.
But the singing of beach sands is quite different from that of desert dunes. The beach sands are best described as “whistling” or “squeaking,” according to R. A. Bagnold, who ably summarizes existing knowledge in the final chapter of his book, The Physics of Blown Sand and Desert Dunes. The squeak or whistle is produced, he explains, by any rapid disturbance of the dry top layer, particularly just above the high water level when the sand has recently dried out after a shower. It is produced when the palm of the hand is swept across it quickly or when the sand is given a light stab with the end of a pencil. When the sand is removed from the beach, it does not long retain its sound-producing quality. Grains of singing beach sand examined were rounded, but not markedly so, and were fairly uniform is size.
In contrast with the whistling of the beach sands, “the great sound which in some places startles the silence of the desert” is quite a different noise, according to R. A. Bagnold. “I have heard it,” he says, “in southwestern Egypt 300 miles from the nearest habitation. On two occasions it happened on a still night, suddenly—a vibrant booming so loud that I had to shout to be heard by my companion. Soon other sources, set going by the disturbance, joined their music to the first, with so close a note that a slow beat was clearly recognized. This weird chorus went on for more than five minutes continuously. . . . Native tales have woven it into fantasy; sometimes it is the song of sirens who lure travelers to a waterless doom; sometimes it is said to come upwards from bells still tolling underground in a sand engulfed monastery. . . .”
The sounds produced by desert dunes certainly vary, for travelers have compared them to a ship’s siren, a throbbing organ, the beat of drums, a trombone, and the twanging of a monster harp. In some instances, it seems that the softer tones are missing; others say that standing on the sand when it is singing is like resting on a huge stringed instrument while a bow is being drawn slowly across it. The note emitted by the desert sand is much lower than that of the beach sand and at a distance of 600 yards has been likened to the rumble of thunder.
Writing from Egypt a year or two ago, Lieutenant Colonel de Lancey Forth spoke of the following experience in the great sand dune country to the south of Siwa, Egypt: “I found, after a strong westerly wind had blown throughout the day and had banked the fine drift sand high up on the knife edged tops of the dunes, that sometimes in the evening, when the wind had died away, leaving a deep stillness in the air, this fine drift sand slid down in streaks over the coarse big-grained red sand which forms the steep slopes of the solid part of the dunes, and the friction of the one rolling over the other gave out a noise like distant rumbling thunder with a deep musical note as that of a cello in it.”
It is interesting that when Mr. St. John Philby was listening to the singing in the afternoon, one of his men referring to the desert spirits, said, “You wait, just wait till the evening and you will hear them letting off their big guns.”
Mr. Bertram Thomas, too, noticed the noise late in the afternoon, when the heat of the day was fading. Apparently, another factor also favors the close of day. During the day the wind blows the fine drift sand to the tops of the dunes, and toward sunset, when the wind usually dies down, it begins to roll down the slopes. Dryness seems an essential factor, for the ancient Chinese manuscript states that the Hill of Sounding Sand gave out notes only at the height of summer; and Mr. Philby likewise testifies that early in the morning, when the air was cool and the sand somewhat moist, he failed to elicit any response from it. And a few weeks later when there had been a little rain, there was no music in the sands.
Examination of the sand has not revealed any peculiarity linking the whistling sands of the beach with the booming sands of the desert. Samples from the dunes do not reveal any distinguishing features. The grains are no more uniform in size than those of many silent sands; and though clean sand sometimes seems to sing best, R. A. Bagnold heard it in a desert region where the sand was dirtier than usual and was wetted appreciably only once or twice in a decade.
A. D. Lewis found that when singing sand was taken from the Kalahari Desert to Pretoria, it lost its “voice” unless kept in airtight containers. But the quality could be restored by heating it to about 390° F.
Scientists generally agree that the sounds are caused by the rubbing of grains against each other, but as yet there is no real explanation of the mechanism by which they are produced. When further critical studies are made, the answers may be forthcoming. Meanwhile, when you are in the desert, keep an ear open for one of the strangest concerts ever to come from nature’s versatile music box.
Source:
No comments:
Post a Comment