Hydrostatics and pneumatics / [Dionysius Lardner].

  • Dionysius Lardner
Date:
1831
Catalogue details

Licence: Public Domain Mark

Credit: Hydrostatics and pneumatics / [Dionysius Lardner]. Source: Wellcome Collection.

    354/376 (page 338)
    force the liquid through the mouth of the tube and over the curved part into the bulb. It will be found, that in this way the bulb and tube will be filled, with the ex- ception of a very small bubble of air, which will remain suspended at the highest point of the tube: this bubble will have the same temperature as the external air, and the same pressure ; and it is obvious, that this is as much lighter than the air which originally filled the tube and bulb, as its present magnitude is less than the whole contents of the bulb and tube. If instead of a glass bulb we take a large spherical bag constructed of any light substance, and having in one part a circular opening or hole, this bag may be distended by blowing into it common air. If the hole be then presented downwards, and a lamp suspended beneath it, the flame of the lamp will gradually increase the temperature of the air contained in the bag : it will thus acquire increased elastic force, by which a part will be expelled at the hole under which the lamp is sus- pended. This process of rarefaction will be continued so long as the air contained in the bag receives increased temperature from the heat of the lamp ; but throughout the whole process the elastic force of the rarefied air will be equql to the external pressure of the atmosphere, and the bag will be subject to no force tending either to burst it or to crush it. Such a bag, if constructed of sufficient magnitude, may by these means be rendered lighter than the air which it displaces. It will thus have a corresponding buoyancy, and will ascend in the atmosphere with a force equal to the difference between its own weight and the weight of the air which it displaces. The application of these principles form the first suc- cessful attempt in aeronautics. In the year 1782, two paper-makers, named Montgolfier, residing at Annonai, in France, constructed a'bag of silk, in the form of a square box, containing about 40 solid feet when filled. In the bottom of this was placed an aperture, under which burning paper was applied: it ascended to nearly 100 feet in the air. The experiment was immediately