Meteorological observations and essays / By John Dalton.

  • John Dalton
Date:
1834
Catalogue details

Licence: Public Domain Mark

Credit: Meteorological observations and essays / By John Dalton. Source: Wellcome Collection.

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    so as to mark at all times the height of the column, in inches and tenths, &c. The instrument thus completed is called a barometer.—It is usual now to blow a pretty capacious bulb at the open end of the tube, and then bend the tube a little above the bulb, so that the bulb may stand upright, leaving a little orifice in it to admit the quicksilver; then the tube being filled as before, upon being inverted, the column of quicksilver in the tube stands at the height of 29 or 30 inches above the surface of that in the bulb, as in the former case. The reason of the fact may be explained thus: every body that supports another, bears all its weight ; therefore, when the surface of any non- elastic fluid is exposed to the air, it bears the weight of a column of air whose base is equal to the said surface, and its height that of the atmo- sphere, supposed to be 40 or 50 miles ; now though air be a very light substance, being in its usual state, at the earth’s surface, about tvth part of the weight of an equal quantity of water, yet so pro- digious a column of it as that above mentioned, has a very considerable weight; moreover, it is a fundamental principle in hydrostatics, that the pressure upon the surface of a fluid must be the same on each part, or the fluid will not rest till that is the case ; if, therefore, the pressure be re- moved from any place of the surface, either wholly or in part, the fluid will yield in that place, and ascend, till the weight of the column of fluid above the surface, together with the pressure upon the