To confirm the probability of this solution of the mystery, it may be mentioned that Baron Humboldt was informed by most credible witnesses, that subterranean sounds, like those of an organ, are heard towards sunrise by those who sleep upon the granite rocks on the banks of the Oroonoko. Those sounds he philosophically supposes may arise from the difference of temperature between the external air and that contained in the narrow and deep crevices of the rocks; the air issuing from which may be modified by its impulse against the elastic films of mica projecting into the crevices; producing, in fact, a natural and gigantic eolina, the simple but beautiful arrangement of musical chords which is now so commonly heard. A somewhat similar phenomenon, which gives rise to an Arab superstition, occurs about three leagues from Tor, on the Red Sea. The spot, which is half a mile from the sea, bears the name of Nakous, or the Bell. It is about three hundred feet high, and eighty feet wide, presents a steep declivity to the sea, and is covered by sand, and surrounded by low rocks, in the form of an amphitheatre. The sounds which it emits are not periodical, but are heard at all hours and at all seasons. The place was twice visited by Mr. Gray. On the first visit, after waiting a quarter of an hour, he heard a low continuous murmuring sound beneath his feet, which, as it increased in loudness, gradually changed into pulsations, resembling the ticking of a clock. In five minutes more it became so powerful as to resemble the striking of a clock, and, by its vibrations, to detach the sand from the surface. When he returned, on the following day, he heard the sound still louder than before. Both times the air was calm, and the sky serene; so that the external air could have had no share in producing the phenomenon; nor could he find any crevice by which it could penetrate. The noise is affirmed by the people of Tor to frighten and render furious the camels that hear it; and the Arabs of the desert poetically ascribe it to the bell of a convent of monks, which convent they believe to have been miraculously preserved under ground. Seetzen, another visiter, attributes the phenomenon to the rolling down of the sand. Rufinus informs us that, when it was destroyed by order of Theodosius, the temple of Serapis at Alexandria was found to be full of secret passages and machines, contrived to aid the impostures of the priests; among other things, on the eastern side of the temple, was a little window, through which, on a certain day of the year, the sunbeams entering fell on the mouth of the statue of Memnon. At the same moment an iron image of the sun was brought in, which, being attracted by a large loadstone fixed in the ceiling, ascended up to the image. The priests then cried out, that the sun saluted their god.