Echoes are frequently mentioned that repeat the sound six or seven times. Such an echo is said by Pliny to have been at a portico in Olympia; another echo, described by Gassendi, near the grave of Metella, repeated a verse of the "Æneid" eight times. Addison heard in Italy a pistol-shot echoed fifteen times. An echo in the county of Argyll repeats the sound eight times after equal pauses, but with diminishing force. These phenomena are favored by the neighborhood of rocks, caves, and bodies of water. Pierre de Castellane, a French officer who served in Algiers, relates that he heard an echo repeated a thousand times on the mountain-road to Bel-Abbes; it seemed to pass from one mountain to another, and to resound from side to side. Admiral Wrangell, in his work on Siberia, tells of an echo at Teheki, near Kirensk, on the Lena, where a pistol-shot is repeated more than a hundred times among the high rocks, and seems like a volley of musketry, but of the force of a cannon-shot.
Partly of the nature of the echo are the peculiar tones which are produced by the wind or the sea in rocky places. The learned Jesuit Kircher describes several such phenomena as sounding like the twanging of the harp, like an organ, or like bells. They have been noticed in Tartary, in Sweden, on the banks of the Guatemala Lake, and at a waterfall in the province of Kiang-si, China. Pausanias speaks of the tuneful waves of the Ægean Sea; Professor Bruder has perceived the chord of the third of C sharp in them. The experiments of the brothers Heim have made it probable that the resonant property resides in some quality of the waters; and Oersted has discussed the subject of the "Harmony of Waterfalls" in his work on the "Spirit of Nature."
The agency of echoes is also observed in the music of grottoes. A fearful sound has been said to be emitted from the grotto of Smaland near Wibourg, in Finland, as if a living animal were imprisoned there. Similar sounds are attributed to grottoes in Switzerland and the island of Hispaniola. A cave near Barable in Hungary gives out a noise like that of a pistol-shot. Harmonious, soothing tones prevail in other caves, as in Fingal's Cave, Staffa, where the falling water-drops, the breezes, and the rolling waves striking upon the basaltic columns, combine to make it a real cave of melodies. The accord of tones in this cave is no doubt attributable in a great degree to the symmetry of its shape, and the regularity of the form and arrangement of the basaltic columns. Other musical sounds proceed from the bosom of a rock called the Piedra de Carichana Vieja, on the banks of the Orinoco; they begin at sunrise, and are attributed to the action of changes of temperature. The musical sounds which are heard on the heights between Mount Sinai and the Gulf of Suez, the bell-tones of the Djebal Nakus rock in the Red Sea, and the noises like thunder in the region of Sinai which are mentioned by Burckhardt, are caused by the rolling of the sands among the rocks.
