Air level

Level Lev"el (l[e^]v"[e^]l), n. [OE. level, livel, OF. livel, F. niveau, fr. L. libella level, water level, a plumb level, dim. of libra pound, measure for liquids, balance, water poise, level. Cf. {Librate}, {Libella}.] 1. A line or surface to which, at every point, a vertical or plumb line is perpendicular; a line or surface which is everywhere parallel to the surface of still water; -- this is the true level, and is a curve or surface in which all points are equally distant from the center of the earth, or rather would be so if the earth were an exact sphere. [1913 Webster]

2. A horizontal line or plane; that is, a straight line or a plane which is tangent to a true level at a given point and hence parallel to the horizon at that point; -- this is the apparent level at the given point. [1913 Webster]

3. An approximately horizontal line or surface at a certain degree of altitude, or distance from the center of the earth; as, to climb from the level of the coast to the level of the plateau and then descend to the level of the valley or of the sea. [1913 Webster]

After draining of the level in Northamptonshire. --Sir M. Hale. [1913 Webster]

Shot from the deadly level of a gun. --Shak. [1913 Webster]

4. Hence, figuratively, a certain position, rank, standard, degree, quality, character, etc., conceived of as in one of several planes of different elevation. [1913 Webster]

Providence, for the most part, sets us on a level. --Addison. [1913 Webster]

Somebody there of his own level. --Swift. [1913 Webster]

Be the fair level of thy actions laid As temperance wills and prudence may persuade. --Prior. [1913 Webster]

5. A uniform or average height; a normal plane or altitude; a condition conformable to natural law or which will secure a level surface; as, moving fluids seek a level. [1913 Webster]

When merit shall find its level. --F. W. Robertson. [1913 Webster]

6. (Mech. & Surv.) (a) An instrument by which to find a horizontal line, or adjust something with reference to a horizontal line. (b) A measurement of the difference of altitude of two points, by means of a level; as, to take a level. [1913 Webster]

7. A horizontal passage, drift, or adit, in a mine. [1913 Webster]

{Air level}, {a spirit level}. See {Spirit level} (below).

{Box level}, a spirit level in which a glass-covered box is used instead of a tube.

{Carpenter's level}, {Mason's level}, either the plumb level or a straight bar of wood, in which is imbedded a small spirit level.

{Level of the sea}, the imaginary level from which heights and depths are calculated, taken at a mean distance between high and low water.

{Line of levels}, a connected series of measurements, by means of a level, along a given line, as of a railroad, to ascertain the profile of the ground.

{Plumb level}, one in which a horizontal bar is placed in true position by means of a plumb line, to which it is at right angles.

{Spirit level}, one in which the adjustment to the horizon is shown by the position of a bubble in alcohol or ether contained in a nearly horizontal glass tube, or a circular box with a glass cover.

{Surveyor's level}, a telescope, with a spirit level attached, and with suitable screws, etc., for accurate adjustment, the whole mounted on a tripod, for use in leveling; -- called also {leveling instrument}.

{Water level}, an instrument to show the level by means of the surface of water in a trough, or in upright tubes connected by a pipe. [1913 Webster]