PHENOMENA OF SOUND.--In the Arctic regions persons can converse at more than a mile distant when the thermometer is below zero. In air, sound travels from 1130 to 1142 feet per second. In water, sound passes at the rate of 4708 feet per second. Sound travels in air, about 900 feet for every pulsation of a healthy person at 75 in a minute. A bell sounded under water may be heard under water at 1200 feet distant. Sounds are distinct at twice the distance on water that they are on land. In a balloon, the barking of dogs on the ground may be heard at an elevation of three or four miles. On Table Mountain, a mile above Cape Town, every noise in it, and even words, may be heard distinctly. The fire of the English on landing in Egypt was distinctly heard 130 miles on the sea. Dr Jameson says, in calm weather he heard every word of a sermon at the distance of two miles! Water is a better conductor of sound than air. Wood is also a powerful conductor of sound, and so is flannel or riband. Sound affects particles of dust in a sunbeam, cobwebs, and water in musical glasses; it shakes small pieces of paper off a string in concord. Deaf persons may converse through deal rods held between the teeth, or held to the throat or breast. Echoes are formed by elliptical surfaces combined with surrounding surfaces, or by such of them as fall into the respective distances of the surface of an ellipse, and are, therefore, directed to the other focus of the ellipse; for all the distances from both foci to such surface are equal, and hence there is a concentration of sounds at those points direct from one focus, and reflected back again from the other focus. An echo returns a monosyllable at 70 feet distance, and another syllable at every 40 feet additional. The echo of artillery is encreased or created by a cloud or clouds. Miners distinguish the substance bored by the sound; and Physicians distinguish the action of the heart or lungs by a listening tube. Gamblers can distinguish, in tossing money, which side is undermost, though covered by the hand. * * * * *