(Fig. 154). When the atmospheric pressure falls, the water at the orifice bulges outwards; when it rises, the water retreats till its surface is slightly concave.
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,