An instrument for the accurate measurement of small differences of height;
esp. of the differences in the height of the upper surfaces of two columns of mercury or other fluid, or of the same column at different times. It consists of a telescopic leveling apparatus
(d), which slides up or down a perpendicular metallic standard very finely graduated (
bb). The telescope is raised or depressed in order to sight the objects or surfaces, and the differences in vertical height are thus shown on the graduated standard.