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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    the water which enters the mouth of the machine. As it descends in the liquid, the air inclosed in it is subject to the pressure which increases in proportion to the depth, and by virtue of its elasticity will become condensed in proportion to this pressure. Thus at the depth of about 34 feet, the hydrostatic pressure will be equal to that of the atmosphere; and since the air at the surface of the water is under the atmospheric pressure, it will be affected by double the pressure at the depth of 34 feet. It will, therefore, conformably to what was explained in (132.) be condensed so much as to be reduced to half its original dimensions. Half the capacity of the machine will, therefore, be filled with water, and the other half will contain all the air which filled the machine at the mo- ment of its immersion. As the depth is increased, the space occupied by the air in the bell will be proportion- ably diminished. It is well known that if an animal continue to respire in a space from which a fresh supply of atmospheric air is excluded, the air confined in the space will at length become unfit for the support of life. This is owing to an effect produced upon the air drawn into the lungs, by which when breathed it contains carbonic acid, an ingre- dient not present in the natural atmosphere, and which is highly destructive to animal life. When the air in which the animal is confined has been breathed for a length of time, this effect being repeated, the air enclosed becomes highly impregnated with this gas; and if its escape be not allowed, and a fresh supply of atmospheric air admitted, the animal cannot live. If, therefore, a diving-bell be used to enable persons to descend in water, it will be necessary either to raise them to the surface after that interval in which the air confined in the bell becomes unfit for respiration, or means must be adopted to send down a supply of fresh air, and to allow the im- pure air to escape. But besides this, there is another reason why means of sending down a supply of air are necessary. It has been already proved, that the hydro- static pressure causes the water to fill a large part of the