File:Airships past and present, together with chapters on the use of balloons in connection with meteorology, photography and the carrier pigeon (1908) (14595549429).jpg

Identifier: airshipspastpres00hild (find matches)
Title: Airships past and present, together with chapters on the use of balloons in connection with meteorology, photography and the carrier pigeon
Year: 1908 (1900s)
Authors: Hildebrandt, A. (Alfred), b. 1870 Story, W. H. tr
Subjects: Aeronautics
Publisher: New York, D. Van Nostrand company
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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equal to that of a column of mercury2992 in. high ; the specific gravity of mercury is 13*59, andtherefore the pressure of the air on a square inch is 14*706 lbs.Let us suppose the air to be contained in a cylinder, which isclosed by an airtight piston, the cross section of the cylinderbeing 1 square inch in area. Let us further suppose that thislittle piece of apparatus is placed beneath the receiver of the airpump. It will then be found that, if the piston is to be kept inposition without allowing the gas in the cylinder to expand, itwill be necessary to load it with a weight of 14*7 lbs. If the pistonis loaded with a weight of 29*4 lbs., the volume of the gas will be THE THEORY OF THE BALLOON. 31 reduced by one half ; the pressure of the gas will therefore bedoubled, and its density similarly increased. Boyle and Mariottehave therefore stated that the volume of a gas is inverselyproportional to its pressure or density. It is now possible with the aid of Boyles law to calculate the
Text Appearing After Image:
Fig. 16. -Stockholm, seen from a height of 1,600 feet. Photograph by OskarHalldin. lift which acts on a balloon at different heights, or withdifferent atmospheric pressures. Let us suppose that the baro-metric pressure is that of 30 in. of mercury, and that the liftis 1,600 lbs. If the pressure sinks to 29 in., the lift will becomefg of 1,600 lbs., i.e., 1,550 lbs. The difference between thesetwo forces is 50 lbs., and corresponds to the weight of about twosacks of ballast. At a height of 6,600 ft. a cubic foot of air 32 AIESHIPS PAST AND PEE SENT. weighs only 0064 lb., and a cubic foot of hydrogen would weigh0*00396 lb. It is therefore possible in this way to determine thegreatest height to which it is possible to ascend, if the dead-weight of the balloon is already known. Hitherto we have assumed the temperature to be constant, andit is necessary to examine the effect produced by its variation.The application of heat increases the volume of any gas. Asimple experiment will make the

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