Cathetometer

n. [From Gr. κάθετος, vertical height, and μέτρον, measure.] An instrument for measuring differences of vertical heights, especially the rise and fall of liquid columns in glass tubes. It consists of a telescopic leveling apparatus (d), which slides up or down a perpendicular metallic standard very finely graduated (bb). As the column rises or falls, the telescope through which it is viewed is correspondingly raised or depressed, and the differences in vertical height are thus shown on the graduated standard.