Lock

a mechanical contrivance used to fasten doors, chests, cupboards, drawers, safes, and the like. The working portions are contained usually in a metal case. The essential working parts are two--a bolt, which is thrown by a key, and a spring to hold the bolt in place. Various devices known as wards are designed to prevent the entrance of a key other than the one belonging to the lock.

Aside from the strength of parts, the value of a lock depends largely on the ingenuity with which the wards are constructed, that is to say, on the skill with which obstructions are arranged to prevent the entrance of a false key. Mortise locks are inserted in a mortise in the lid or door. Rim locks are fastened usually to the inner face of the door. The locks of the ancient Egyptians, Greeks, and Romans were made usually of hard wood. They were little more than wooden bolts. A remarkable wooden lock Invented by the Egyptians is still in use, it is said, in Turkey. The bolt contains three holes into which three upright, concealed pins fall when it is shot. The bolt is hollow. When it is desired to release the bolt a slip of wood having three pegs on its upper surface is thrust into the hollow and lifted. The pegs are thus brought into play to lift the pins. This rude contrivance is considered the ancestor of the modern lock and key.

The locksmith of the Middle Ages was an ingenious workman. His locks were made by hand. They were large, ornate affairs. The keys were much too large for the pocket. The housekeeper, the porter, the steward, the monk in charge of the cellars, the jailer, and the merchant fastened their keys to a belt or girdle. The business was combined usually with that of making cutlery and later the locksmith became a gunsmith as well.

Of modern locksmiths, none is more noted than Linus B. Yale of New York, the inventor of the Yale lock. In place of the pins of the Turkish lock, he uses a large number of small metal disks or tumblers, each of which holds the bolt from slipping. The key, which raises them, is a thin slip of metal, possibly two inches in length, having one edge cut into a series of zigzags or notches. The set of tumblers and zigzag of the key match. Only the most skilful locksmith can pick a Yale lock without the individual key made for it.

For time locks, see SAFE.