. The principles of physics. Fig. 126. 158 MOLAR DYNAMICS. A pressure of 15 pounds per square inch is quite generallyadopted by engineers as a unit of gaseous pressure, and iscalled an atmosphere. Physicists, however, generally measurepressure in terms of cm or mm of mercury at 0° C.; that is,the hight in m,m of mercury that the pressure of the atmos-phere sustains in the Fig. 127. 131. The barometer. — The hight of the col-umn of mercury supported by atmospheric pres-sure is quite independent of the area, of thesurface of the mercury pressed upon ; hence theapparatus is more convenient
. The principles of physics. Fig. 126. 158 MOLAR DYNAMICS. A pressure of 15 pounds per square inch is quite generallyadopted by engineers as a unit of gaseous pressure, and iscalled an atmosphere. Physicists, however, generally measurepressure in terms of cm or mm of mercury at 0° C.; that is,the hight in m,m of mercury that the pressure of the atmos-phere sustains in the Fig. 127. 131. The barometer. — The hight of the col-umn of mercury supported by atmospheric pres-sure is quite independent of the area, of thesurface of the mercury pressed upon ; hence theapparatus is more conveniently constructed inthe form represented in Fig. 127. A straight tube about 34 inches long is closedat one end and filled with mercury. The tube isinverted, with its open end tightly covered witha finger, and this end is inserted into a vessel ofmercury. When the finger is withdrawn the Fig. 128. THE FORTIN BAROMETEB. 159 mercury sinks until there is equilibrium between the down-ward pressure of the mercurial column AB and the pressureof the atmosphere. The empty space at the top of the tubeis called a Torricellian vacuum. An apparatus designed tomeasure atmospheric pressure is called a barometer (pressure-measurer). A common cheap form of barometer is repre-sented in Fig. 128. Beside the tube and near its top is ascale graduated in inches or centimeters, indicating the h
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectphysics, bookyear1895
