Airships past and present, together with chapters on the use of balloons in connection with meteorology, photography and the carrier pigeon . h less than when it is weighed inthe open air. It is therefore necessary to understand theproperties of the air and of the gases used for filling balloons,before any adequate conception of the principles underlyingtheir movements can be formed. The air may be looked upon as a mixture of 79 per cent, ofnitrogen with 21 per cent, of oxygen. Gases have a tendency todiffuse themselves on all sides; they have therefore great 28 AIRSHIPS PAST AND PRESENT. elas
Airships past and present, together with chapters on the use of balloons in connection with meteorology, photography and the carrier pigeon . h less than when it is weighed inthe open air. It is therefore necessary to understand theproperties of the air and of the gases used for filling balloons,before any adequate conception of the principles underlyingtheir movements can be formed. The air may be looked upon as a mixture of 79 per cent, ofnitrogen with 21 per cent, of oxygen. Gases have a tendency todiffuse themselves on all sides; they have therefore great 28 AIRSHIPS PAST AND PRESENT. elasticity and can be easily compressed. The weight of a cubicfoot of the atmosphere at a temperature of 32° Fahr. and apressure of 29*92 in. of mercury, is 0*0807 lb.; the weight of acubic foot of hydrogen under the same conditions is only0*0056 lb., and of a cubic foot of coal gas about 0*04 lb. on anaverage. The law of Archimedes therefore states that a cubicfoot of hydrogen will be acted upon by an upward force of0*0751 lb., and that the force acting on a cubic foot of coal gaswill be similarly 0*0407 lb. Here we have assumed that the. Fig. 14.—The Baroscope. hydrogen is chemically pure. In point of fact, the above figuresare slightly too high, in so far as ordinary samples of hydrogenand coal gas are concerned. But allowance must be made for the weight of the car, net,ropes, and other appurtenances, in calculating the effectiveupward force acting on the balloon. It will therefore be evidentthat the size must be considerable if it is to be capable of risingin the air. The following example will perhaps make this us suppose that the weight of a balloon with its appurtenancesis a quarter of a ton, and that its capacity is 21,000 cubic feet. Theweight of the air displaced by it is 1,700 lbs., and on the other hand,the weight of the contained hydrogen is only 118 lbs. Consequently THE THEORY OF THE BALLOON. 29 the net upward force is 1,022 lbs. If the expedition is t
Size: 1798px × 1390px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookpubl, booksubjectaeronautics
