PLUMMET

(Lat. plumbum, /earf.) A heavy body (usually a piece of lead, whence the name) suspended by a flexible thread for the purpose of indicating the perpendicular to the horizon, or the direction of terrestrial gravity. In former times, the plumb-line constituted an e ential part of the apparatus employed for adjusting astronomical instruments; but it is seldom used in modern observations, excepting those made with the zenith sector, its place being either more conveniently supplied by the spirit level, or ths method of determining the zenith point by combining direct and reflected observations rendering it unnece ary. For the common artificer's plummet, see Level. [s. 953]