Page:Wonderful Balloon Ascents, 1870.djvu/226

210 ascents are very interesting. He found that in no instance did the temperature of the air decrease uniformly with the increase of height. In fact, the decrease in the first mile is double that in the second, and nearly four times as great as the change of temperature in the fifth mile. The distribution of aqueous vapour in the air is no less remarkable. The temperature of the dew-point on leaving the earth decreases less rapidly than the temperature of the air; so that the difference between the two temperatures becomes less and less, till the vapour or cloud plane is reached, when they are usually together, and always most nearly approach each other, and that point is usually at about the height of one mile. On leaving the upper surface of cloud, the dew point decreases more rapidly than the air, and at extremely high situations the difference between the two temperatures is wonderfully great, indicating an extraordinary degree of dryness, and an almost entire absence of water. Under these circumstances, the presence of cirrus clouds far above this dry region, apparently as much above as when viewed from the earth, is very remarkable, and leads to the conclusion that they are not composed of water.

In the propagation of sound, M. Glaisher made many curious experiments. In one ascent (July 17th) he found, when at a distance of 11,800 feet above the earth, that a band was heard; at a height of 22,000 feet, a clap of thunder was heard; and at a height of 10,070 feet, the report of a gun was heard. On one occasion, he heard the dull hum of London at a height of 9,000 feet above the city, and on another occasion, the shouting of many thousands of persons could not be heard at the height of 4,000 feet.