church. In the strict sense of the word, there is no Catholic church in being; that is, no universal Christian Communion.

CATOPTRICS, that part of optics which explains the properties of reflected light, and particularly that which is reflected from mirrors.

CAVALIER, an armed horseman or knight, called by the French a chevalier.

CAVALRY, a body of soldiers that charge on horseback. Their chief use is to make frequent excursions to the disturbance of the enemy, intercept his convoys, and destroy the country; in battle, to support and cover the foot, to break through and disorder the enemy, and to secure the retreat of the foot.

CAVEAT, an entry in the Spiritual Courts, by which the probate of a will, letters of administration, licence of marriage, &c. may be prevented from being issued without the knowledge, and, if the reason be just, the consent of the party entering the caveat.

CAUKING, or caulking a ship, is driving a quantity of oakum into the seams of the planks. After the oakum is driven very hard into these interstices, it is covered with melted pitch to keep the water from rotting it.

CAUSE, that from whence any thing proceeds, or by virtue of which any thing is done: it stands opposed to effect. We get the ideas of cause and effect from our observation of the vicissitude of things, while we perceive some qualities or substances begin to exist, and that they receive their existence from the due application and operation of other beings. That which produces is the cause;

and that which is produced, the effect: thus, fluidity in wax is the effect of a certain degree of heat, which we observe to be constantly produced by the application of such heat.

CAUSEWAY, a common, hard, raised road, made for the convenience of travelling.

"CAUSTIC, in chemistry, a fixed alkaline salt, deprived of its carbonic acid, and most of its water by means of quick lime, evaporation and fusion. The alkali used for this purpose is generally pot-ash, and the form that is chosen is the lixivium of the soap-boilers, which is evaporated to dryness in a copper or silver vessel, fused in a crucible, poured into a bason, and when solid cut into small pieces, which must be kept in a bottle well closed to prevent deliquescence. If a piece of this caustic be applied to the skin, it corrodes it in about half or three quarters of an hour, producing a painful eschar like that which is occasioned by burning; and forming most probably a saponacious compound with the fat-parts of the skin, or flesh.

CAUTERY, in surgery, a remedy by which solid parts of the body may be burnt, ate, or corroded away. The actual cautery is a red-hot instrument, usually of iron; the potential cautery, a corroding substance.

CEMENT, in a general sense, any glutinous substance capable of uniting and keeping things together in close cohesion. In this sense the word cement comprehends mortar, solder, glue, &e. but has been generally restrained to the compositions used for holding together broken glasses, china, and earthenware. For this purpose the juice of garlick is recommended as exceedingly proper,