THE ANEROID BAROMETER.
On account of their size and weight, and the comparative difficulty of transporting them without derangement of the mercury column, column barometers are not so generally used as the aneroid variety. Aneroid means "without moisture," and in this particular connection signifies that no liquid is used in the construction of the barometer.
Fig. 155 shows an aneroid in detail. The most noticeable feature is the vacuum chamber, V C, a circular box which has a top and bottom of corrugated but thin and elastic metal. Sections of the box are shown in Figs. 156, 157. It is attached at the bottom to the base board of the instrument by a screw (Fig. 156). From the top rises a pin, P, with a transverse hole through it to accommodate the pin K E, which has a triangular section, and stands on one edge.