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.
Chapter IV. Balloons Made Useful in Warfare.
Wars of the French Republic--Company of "Ballooneers"--Battle of
Fleurus--The Balloons of Egypt--Napoleon--Modern Services War in
Italy--War in America--Conclusion.
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