SOUNDS AND ECHOES.
Sound is propagated successively from the sounding body to the places which are nearest to it, then to those more distant, &c. Every observer knows that when a gun is fired at a considerable distance from him, he perceives the flash a certain time before he hears the report; and the same thing is true with respect to the stroke of a hammer, or of a hatchet, the fall of a stone, or, in short, any visible action which produces a sound or sounds. In general, sound travels through the air at the rate of eleven hundred and forty-two feet in a second, or about thirteen miles in a minute. This is the case with all kinds of sounds; the softest whisper flying as fast as the loudest thunder. Sound, like light, after it has been reflected from several places, may be collected into one point as a focus, where it will be more audible than in any other part; and on this principle whispering galleries are constructed. The particulars relative to the celebrated whispering gallery in the dome of St. Paul’s church, London, will be comprehended in the description of that noble edifice.
An echo is the reflection of sound striking against a surface adapted to the purpose, as the side of a house, a brick wall, hill, &c., and returning back again to the ear, at distinct intervals of time. If a person stand about sixty-five or seventy feet from such a surface[a surface], and perpendicularly to it, and speak, the sound will strike against the wall, and be reflected back, so that he will hear it as it goes to the wall, and again on its return. If a bell situated in the same way be struck, and an observer stand between the bell and the reflecting surface, he will hear the sound going to the wall, and also on its return. Lastly, if the sound strike the wall obliquely, it will go off obliquely, so that a person who stands in a direct line between the bell and the wall will not hear the echo. According to the greater or less distance from the speaker, a reflecting object will return the echo of several, or of fewer syllables; for all the syllables must be uttered before the echo of the first syllable reaches the ear, to prevent the confusion which would otherwise ensue. In a moderate way of speaking, about three and a half syllables are pronounced in one second, or seven syllables in two seconds: therefore, when an echo repeats seven syllables, the reflecting object is eleven hundred and forty-two feet distant; for sound travels at the rate of eleven hundred and forty-two feet per second, and the distance from the speaker to the reflecting object, and again from the latter to the former, is twice eleven hundred and forty-two feet. When the echo returns fourteen syllables, the reflecting object must be twenty-two hundred and eighty-four feet distant, and so on.
The most remarkable echo recorded, is at the palace of a nobleman, within two miles of Milan, in Italy. The building is of some length in front, and has two wings jutting forward; so that it wants only one side of an oblong figure. About one hundred paces before the mansion, a small brook glides gently; and over this brook is a bridge forming a communication between the mansion and the garden. A pistol having been fired at this spot, fifty-six reiterations of the report were heard. The first twenty were distinct; but in proportion as the sound died away, and was answered at a greater distance, the repetitions were so doubled that they could scarcely be counted, the principal sound appearing to be saluted in its passage by reports on either side at the same time. A pistol of a larger caliber having been afterward discharged, and consequently with a louder report, sixty distinct reiterations were counted. From this example it follows, that the further the reflecting surface is, the greater number of syllables the echo will repeat; but that the sound will be enfeebled nearly in the same proportion, until at length the syllables can not be distinctly heard. On the other hand, when the reflecting object is too near, the repetition of the sound reaches the ear, whilst the perception of the original sound still continues, in which case an indistinct resounding is heard, as may be observed in empty rooms, passages, &c. In such places, several reflections from the walls to the hearer, as also from one wall to the other, and then to the hearer, clash with each other, and increase the indistinctness of the sound.
BURIED CITIES.
THE YANAR, OR PERPETUAL FIRE.
Before passing on to the buried cities of Herculaneum and Pompeii, it may be as well to notice a singular phenomenon, supposed by some to be of volcanic origin, viz., the Yanar, or perpetual fire. Captain Beaufort, of the British navy, among the interesting details of his survey of Karamania, on the south coast of Asia Minor, describes this curious phenomenon; and from his account the following particulars are extracted, as supplementary to and connected with the details of volcanoes and their effects.
Having perceived during the night a small but steady light among the hills, he found that this was represented by the inhabitants as a yanar or volcanic light; and on the following morning curiosity led him to visit the spot. In the inner corner of a ruined building he came to a wall, so undermined as to leave an aperture of about three feet in diameter, and shaped like the mouth of an oven. From this aperture the flame issued, giving out an intense heat, but without producing any smoke on the wall; and although several small lumps of caked soot were detached from the neck of the opening, the walls were scarcely discolored. Trees, brushwood and weeds, grew close around this little crater; a small stream trickled down the hill in its vicinity; and the ground did not appear to feel the effect of its heat at more than a few yards’ distance. No volcanic productions were perceived near to it; but at a short distance, lower down on the side of the hill, was another hole or aperture, which had apparently been at some remote period the vent of a similar flame. It was asserted, however, by the guide, that, in the memory of the present race of inhabitants, there had been but one such volcanic opening, and that its size and appearance had been constantly the same. He added, that it was never accompanied by earthquakes or noises; and that it did not eject either stones, smoke or noxious vapors; but that its brilliant and perpetual flame could not be quenched by any quantity of water. At this flame, he observed, the shepherds were in the habit of cooking their food. This phenomenon appeared to Captain Beaufort to have existed for many ages, and he was persuaded that it is the spot to which Pliny alludes in the following passage: “Mount Chimera, near Phaselis, emits an unceasing flame, which burns day and night.” Within a short distance is the great mountain of Takhtalu, the naked summit of which rises, in an insulated peak, seventy-eight hundred feet above the level of the sea. In the month of August a few streaks of snow were discernible on the peak; but many of the distant mountains of the interior were completely white for nearly a fourth the way down their sides. It may hence be inferred, that the elevation of this part of Mount Taurus is not less than ten thousand feet, which is equal to that of Mount Etna.
Such a striking feature as this stupendous mountain, in a country inhabited by illiterate and credulous people, can not fail to have been the subject of numerous tales and traditions. Accordingly, the captain was informed by the peasants, that there is a perpetual flow of the purest water from the very apex; and that notwithstanding the snow, which was still lingering in the chasms, roses blew there all the year round. He was assured by the agha of Deliktash, that every autumn a midnight groan is heard to issue from the summit of the mountain, louder than the report of any cannon, but unaccompanied by fire or smoke. The agha professed his ignorance of the cause, but on being pressed for his opinion, gravely replied, that he believed it was an annual summons to the elect, to make the best of their way to Paradise. However amusing this theory may have been, it may possibly be true that such explosions take place. The mountain artillery heard by Lewis and Clarke, among the Rocky mountains, and similar phenomena which are said to have occurred in South America, seem to lend some probability to the account. The natives have also a tradition, that when Moses fled from Egypt, he took up his abode near this mountain, which was therefore named Moossa-Daghy, or the mountain of Moses. Between this story, and the Yanar, as it has been described above, may there not have been some fanciful connection? The site of this volcanic opening is at an inconsiderable distance from the mountain; and the flame issuing from the thicket which surrounds it, may have led to some confused association with the burning bush on Mount Horeb, of which we have the account in the book of Exodus.