The name Jebel Nagous, or the Mountain of the Bell, became attached to a remarkable acoustic phenomenon in the Sinai desert: a deep sound associated with moving sand. In 1889 the chemist H. Carrington Bolton investigated the slopes and published his observations. His surviving account supplies a useful distinction between the existence of the sound, the conditions in which he heard it, and the question of how a mass of grains produces a sustained musical note.
The principal original source reviewed here is Bolton’s letter “The Angle of Rest for Dry Sand”, The Engineering and Mining Journal, 21 September 1889, page 244. The full letter appears in the right-hand column of the journal page reproduced above. It is signed in New York on 18 September and describes observations made during his earlier journey in Egypt and Sinai, not an experiment conducted in New York.
The mountain and the moving sand
Bolton describes several sand slopes on Jebel Nagous. His largest measured approximately 390 feet along its height, with a broad base of about 260 feet tapering sharply towards the top. He also estimated a substantial thickness of sand at the base. These are the dimensions he reported in 1889, rather than a modern survey of a slope that may since have changed.
In his account, wind carried fine sand up from the relatively level ground at the mountain’s foot. The material accumulated until the slope exceeded the inclination at which it could remain at rest. It then flowed down, sometimes spontaneously. Bolton compared its motion to a slowly flowing viscous substance and recorded a loud bass note accompanying it.
This observation connects the acoustic event with moving sand at the site. It is more informative than an unexplained noise heard somewhere in a desert. It also keeps wind’s role in perspective: wind can supply and redistribute the sand, while the reported sound accompanies the subsequent flow. Those are separate stages in the account.
Why the angle mattered
Bolton’s immediate purpose in writing to the engineering journal was to discuss the maximum slope of dry sand. Using a clinometer during his journey, he repeatedly obtained a value close to 31 degrees for the fine sand he encountered. He contrasted this with values published in several engineering handbooks, some of which were considerably steeper.
The letter records a dozen measurements in the desert and an example at another locality, Ojrat Ramadan, where the upper and lower parts of a sand slope had different inclinations. It also gives grain measurements supplied by his collaborator Alexis A. Julien. These details show that he was comparing material and slope conditions, rather than simply declaring that every kind of dry sand everywhere must behave identically.
His request to readers was for better data in which the size of the grains had actually been measured. The editor’s short reply supplied another practical handbook value but acknowledged the absence of grain-size data. The exchange illustrates a live measurement problem: the same general label, “dry sand”, could conceal differences relevant to the reported angle.
A preliminary investigation
Bolton referred readers to an earlier account in Nature, 25 April 1889, “A New Mountain of the Bell”. Its accessible opening identifies the Mountain of the Bell on the Gulf of Suez, reached from Tor by a roundabout camel route. He said his observations broadly agreed with earlier travellers, although some measurements differed. The full subscription text was not available in this review; it is not treated here as a fully examined source.
The September letter is narrower and directly readable in its original printed form. It documents an observer’s description and measurements, but supplies no acoustic waveform, sound recording or frequency spectrum. Its statement that a bass note accompanied flowing sand can be assessed as historical field testimony without attributing modern instruments to an expedition that did not use them.
What later experiments can explain
A later experimental paper, “The song of the dunes as a self-synchronized instrument”, by Stéphane Douady and colleagues, investigated singing sand using controlled laboratory and field experiments. It associated sustained sound with relative grain motion and proposed synchronisation within the flowing layer. Its experiments demonstrated that suitable sand could produce a sustained tone without requiring the whole dune as a resonating body.
That research helps explain why flowing sand can be musical, but it was not a new measurement of Bolton’s Sinai slope. The sites listed in its comparison table are elsewhere. Its proposed detailed mechanism should therefore remain attributed to that study, rather than being described as a complete retrospective instrumental solution of every nineteenth-century report from Jebel Nagous.
Assessment and map location
Outcome: Closed (Explained). For the phenomenon described in Bolton’s reviewed field account, moving sand is the documented source of the bass sound. Later experiments establish a natural acoustic process for singing sand. This classification concerns the sound accompanying sand flow; it does not claim to reconstruct every historical noise at the mountain or to settle all details of grain-scale sound generation there.
Map location: the pin at 28.33, 33.54 is an approximate mountain-area reference, rounded from the GeoNames entry for Gebel Naqus/Jabal Naqus in South Sinai, at about 28.3304 N, 33.5425 E. It is not a surveyed outline of Bolton’s sandbank, a measured instrument position, a trailhead or a visitor entrance. Other gazetteers place the named feature somewhat differently, so the pin must not be read as exact experimental-site coordinates.
No current permission, route or safe public access to the slope has been verified. The record uses 1889 for Bolton’s documented investigation and preserves publication dates separately. It does not invent an exact visit day from the dates of his letters. Sources and metadata checked on 13 November 2026.