TERREPLEIN. In fortification, the horizontal surface of the rampart in rear of the parapet.
TERRESTRIAL REFRACTION. The property of the atmosphere by which objects appear to be higher than they really are, and in certain cases producing the effect called deceptio visus, and fata morgana.
TERRITORY. The protection of neutral territory operates to the restitution of enemy's property captured within its limits. Since the introduction of fire-arms that distance has usually been recognized to be almost three English miles.
TERTIATE, To. To examine whether a piece of ordnance is truly bored and has its due proportion of metal in every part, especially at the vent, the trunnions, and the muzzle.
TESTING A CHAIN-CABLE. Trying its strength by the hydraulic machine, which strains it beyond what it is likely to undergo when in use.
TESTONE. A silver Papal coin, value 1s. 3d. A testone is also a current coin in Portugal, consisting of 100 reis.
TETE DE PONT. A work covering the farther end of a bridge from assault from the country beyond.
TEW, To. To beat hemp.
THAUGHTS (properly Athwarts). See [Thwarts].
THEODOLITE. The theodolite, as used in land-surveying, levelling, &c., is well known. But the great theodolite, with its vertical circle and telescope adapted to the observation of the heavenly bodies, as used by nautical astronomers, commonly called an alt-azimuth instrument, is almost an observatory per se. By this alone, within three hours on each side of noon, the longitude, latitude, and magnetic variation of a position may be determined.