Mercury barometer which can lie horizontally without vacuum loss - has end of capillary in reservoir bent into protrusion at back of scale plate

摘要

The capillary tube (5) at the base of the column is bent through 90 deg. so that its open end is in a protrusion (6) at the rear and bottom of the mercury reservoir (1). The reservoir is sealed (3) by a cap which retains the mercury but allows atmospheric pressure to reach surface of the mercury (2). If the barometer is laid flat, so that the back plate (4) is horizontal, the end of the capillary tube is still immersed, thus stopping air from spoiling the vacuum in the column. When hung on a wall or lying down, the reservoir is protected by stand-off pins on the back of the plate (4).