1. A levelling instrument in which water is used instead of alcohol (see quot. 1880).
1563. Shute, Archit., B ij b. Geometrie teacheth vs the order of rules, Compasses, Squiers, Quadrantes, and Iuste water-leueles with manie other knowlaiges.
1674. R. Hooke, Animadv. Hevelius, 61. This is done by the help of a Water-Level.
1723. E. Stone, trans. Bion’s Math. Instrum., V. i. (1758), 134. The first of these Instruments is a Water-Level, composed of a round Tube of Brass, or other solid Matter, about 3 Feet long [etc.]…. This Level, altho’ very simple, is very commodious for levelling short Distances.
1880. L. D’A. Jackson, Aid Surv.-Pract., 146. The water level … is also an appliance for rough levelling within short distances…. It consists of a horizontal tube about two feet long terminated by two bottle-shaped ends, in which water will stand level and thus afford a horizontal line of sight.
2. Mining. A road driven on the strike of a seam to carry off water.
1698. Phil. Trans., XX. 368. It is only a Spring which rises in a Coal-Drift (or Water Level made for the draining of the Cannel Coal-Pits).
1836. Hull & Selby Rlwy. Act, 43. Airways, headways, gateways, or water-levels through the mines.
1886. J. Barrowman, Sc. Mining Terms, 71.
3. The plane below which the rock or soil is saturated with water; the situation of this plane. Also attrib.
1839. Ure, Dict. Arts, 960. To whatever depth a coal-mine is drained of its water, from that depth it is worked, up to the rise of the water-level line. Ibid., 974. The miner … is guided in his line of direction entirely by the water-level.
1882. Geikie, Text-bk. Geol., III. II. ii. § 2. 345. In most districts rocks are permeated with water below a certain limit termed the water-level.
4. The horizontal surface of still water. Also the (higher or lower) position of the surface of water.
1860. Maury, Phys. Geog. Sea (Low), xii. 297. Thus we might have a sea whose level would be much further below the water-level of the ocean than is the Dead Sea.
1862. Smiles, Engineers, III. iii. 26. When the water-level in the pit was lowered, and the suction became incomplete [etc.].
1878. D. Kemp, Man. Yacht Sailing, 377. A straight line from the fore side of the stem to the aft side of the stern-post at the water level.
1895. J. J. Raven, Hist. Suffolk, 39. The salting mound just above the present average water-level in Herringfleet.
1917. L. Einstein, Inside Constantinople, v. 212. They [the crew] succeeded in raising the stern [of the submarine] to the water-level, whence all scrambled out.
