Hydrostatics and pneumatics / [Dionysius Lardner].

  • Dionysius Lardner
Date:
1831
Catalogue details

Licence: Public Domain Mark

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

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    which pressure is transferred to the base of the solid by the inferior strata of liquid. Now this property of transmitting pressure is common to elastic fluids, and we are, therefore, warranted in the inference, that a solid suspended in a gaseous fluid, which is lighter, bulk for bulk, than the fluid, will rise; that if it be heavier, bulk for bulk, it will fall; and if it be equal in weight, bulk for bulk, it will remain suspended. That a solid, there- fore, may rise in the atmosphere with any given force, it is only necessary that its weight should be less than the weight of the air which it displaces by the amount of that force. Upon this principle balloons are con- structed. The method of constructing a balloon, which natu- rally first suggests itself, is to exhaust a large chamber of the air which it contains, so as to render it a vacuum, or nearly so : it will then continue to displace the same quantity of atmosphere as before, but its weight will be diminished by the weight of the air withdrawn from the chamber, and it will have a disposition to rise in the atmosphere proportionate to the difference between the actual weight of the materials which form the chamber and the weight of the air whose place it occupies. This was, accordingly, the method adopted in the earliest attempts on record to construct balloons. About the middle of the seventeenth century, a Jesuit named Fran- cis Lana constructed four hollow spheres of copper, each twenty feet in diameter, and so thin that the total weight of the copper composing them was less than the weight of the air which they would displace. He proposed to attach these spheres to a boat fur- nished with a sail, as represented in Jig. 46., by which means he hoped to traverse the clouds. The method of exhaustion which Lana possessed was insufficient to accomplish his purpose; but even had it been otherwise, the atmospheric pressure acting on the external surface of the attenuated metal globes would have crushed them, and proved the project to be im- practicable. It may be stated generally, that no known