TRONA. An article of export from Tripoli and Egypt; the natron of commerce, and over munnoo of the East Indies. Sesqui-carb. of soda mixed with salt and sulphate of soda.
TROOP. A company of cavalry, commanded by a captain, generally from forty to sixty strong. Also, an assembling beat of the drum.—Trooping the guard, or the colours, are special military ceremonies connected with guard-mounting.—Troop the guard. A ceremony daily practised in large ships by the marines at morning muster.
TROOP-BOATS. Are built with great flatness of floor, with extreme breadth, carried well forward and aft, and possessing the utmost buoyancy, as well as capacity for stowage. They were carried as paddle-box boats (inverted), and thus protected the paddles as well as being ready for use.
TROOP-SHIPS. A class of vessel of excellent account, during war, in the hands of government; far preferable to hired transports for the purpose of conveying soldiers, especially cavalry and their horses. They were usually, in the last French war, 50's and 64's; and with the lower-deck guns taken out, were roomy and airy.
TROPHY. Anything captured from an enemy and shown or treasured as a token of victory.
TROPICAL MOTION. See [Motion].
TROPICAL REVOLUTION. If the periodic time of a circuit round the sun be taken in reference to the equinoxes or tropics, it is called a tropical revolution.
TROPIC-BIRD. Phaethon æthereus, a well-known sea-bird, distinguished by two very long feathers in its tail; also termed boatswain-bird, from the tail feathers resembling a marline-spike.
TROPICS. Two imaginary lines upon the globe, or lesser circles of the sphere, parallel to the equator, and at 231⁄2° distance on each side of it; they touch the ecliptic at its greatest distances from the equator, and from the boundaries of the sun's declination, north and south.
TROUGH [from the Anglo-Saxon troh]. A small boat broad at both ends. Also, the hollow or interval between two waves, which resembles a broad and deep trench perpetually fluctuating. As the set of the sea is produced by the wind, the waves and the trough are at right angles with it; hence a ship rolls heaviest when she is in the trough of the sea.