"They are heard sometimes flying in this direction, then in the opposite through the air; mostly, they are heard as though coming down out of the sky; but at other times as if rising from the ground. They resemble occasionally various musical instruments; occasionally also the clash of arms, or the rattle of drums, or the blare of trumpets. Sometimes they are like the tramp of horses, or the discharge of distant artillery. But sometimes, also, they consist in an indescribably hollow, thrilling, sudden scream. Very commonly they resemble all kinds of animal tones, mostly the barking of dogs. Quite as often they consist in a loud call, so that the startled hearer believes himself to be called by name, and to hear articulate words addressed to him. In some instances, Greeks have believed they were spoken to in the language of Hellas, whereas Romans supposed they were addressed in Latin. The modern Highlanders distinctly hear their vernacular Gaelic. These aërial voices accordingly are so various that they can be interpreted differently, according to the language of the hearer, or his inner conception of what they might say." The Jews call the mysterious voice that falls from the heaven Bathkol, and have many traditions relative to it. The sound of arms and of drums and artillery may safely be set down to the real vibrations of arms, drums, and artillery at a great distance, carried by the wind. In the desert of Gobi, which divides the mountainous snow-clad plateau of Thibet from the milder regions of Asia, travellers assert that they have heard sounds high up in the sky as of the clash of arms or of musical martial instruments. If travellers fall to the rear or get separated from the caravan, they hear themselves called by name. If they go after the voice that summons them, they lose themselves in the desert. Sometimes they hear the tramp of horses, and taking it for that of their caravan, are drawn away, and wander from the right course and become hopelessly lost. The old Venetian traveller Marco Polo mentions these mysterious sounds, and says that they are produced by the spirits that haunt the desert. They are, however, otherwise explicable. On a vast plain the ear loses the faculty of judging direction and distance of sounds; it fails to possess, so to speak, acoustic perspective. When a man has dropped away from the caravan, his comrades call to him; but he cannot distinguish the direction whence their voices come, and he goes astray after them. Rubruquis, whom Louis IX. sent in 1253 to the court of Mongu-Khan, the Mongol chief, says that in the Altai Mountains, that fringe the desert of Gobi, demons try to lure travellers astray. As he was riding among them one evening with his Mongol guide, he was exhorted by the latter to pray, because otherwise mishaps might occur through the demons that haunted the mountains luring them out of the right road.