The weight or pressure of the atmosphere is equal to the weight of a column of water 34 feet in height, or to a column of mercury 30 inches in height, or to 14.7 lbs. average per square inch, at a mean temperature. But air, like all other gases, is rendered lighter by the application of heat; for then the particles of the mass are repelled from each other, or rarefied, and occupy a greater space. Rarefied air, being specifically lightest, mounts above that of common density; hence change of temperature, and the principle cause of winds.

Table Of The Expansion Of Atmospheric Air By Heat

The pressure or gravity of the atmosphere, being equal to a column of water 34 feet in heieht, is the means or principle on which rests the utility of the common pump, also of the syphon and all other such hydraulic applications. In a pump, the internal pressure on the surface of the liquid is removed by the action of the bucket; and as by degrees the density becomes lessened, so the water rises by the external pressure to the above named height; and at such height it will remain, unless, by some derangement of construction taking place, the atmospheric fluid is allowed to enter and displace the liquid column. But observe, if the temperature of the water or other liquid bo so elevated that steam or vapor arise through it, then, according to the vapor's accumulation of density, may the action of the pump be partially or wholly destroyed; and the only means of evasion in such cases is, to place the working bucket beneath the surface of the liquid which is required to be raised.

Size, Length, Breadth And Weight