LOBBY, (from the German lanbe,) a small hall or wait ing-room, or the entrance into a principal apartment, where there is a considerable space between it and a portico or ves tibule, but the length or dimensions will not allow it to be considered as a vestibule or ante-room.
LOCK, (from the Saxon, toe) a well-known instrument used for fastening doors, chests, &c., generally opened by a key. The lock is reckoned the master-piece in smithery ; a great deal of art and delicacy being required in contriving and varying the wards, springs, bolts, &c., and adjusting them to the places where they are to be used, and to the several occasions of using thorn. From the various structure of locks, accommodated to their different intentions, they acquire various names. Those placed on outer doors are called stock-locks ; those on chamber-doors, spring-locks ; those on trunks, trunk-locks, padlocks, &c. Of these the spring-lock is most considerable, both for its frequency and the curiosity of its structure. Its principal parts are the main-plate, the cover-plate, and the pin-hole : to the main plate belong the key-hole, top-hook, cross-wards, bolt-toe, or bolt-knab, drawback-spring tumbler, pin of the tumbler, and the staples ; to the cover-plate belong the pin, mainward, cross-ward, step-ward, or dap-ward ; to the pin-hole belong the hook-ward, main cross-ward, shank, the pot or bread-bow-ward and bit.
The principle on which all locks depend is the application of a lever to an interior bolt, by means of a communication from without ; so that by means of the latter, the lever acts upon the bolt, and in such a manner as to secure the lid or door from being opened by any pull or push from without.
The seeurity of locks in general therefore depends on the number of impediments we can interpose betwixt the lever (the key) and the bolt which secures the door ; and these impediments are well known by the name of 7PUrdS, the number and intricacy of which alone are supposed to distiu guish a good lock from a bad one. If these wards, however, in an effectual manner, preclude the access of all other instruments beside the proper key, it is still possible fir a mechanic of equal skill with the lockmaker, to open it with out the key, and thus to elude the labour of the other. The excellence of locks consists in the security they atlord ; and as numberless schemes are continually brought forward by designing men, to elude every contrivance of the most ingenious mechanics, the invention of a durable lock, so constructed as to render it impossible for any person to open it without its proper key, has ever been an object of con siderable importance.
Locg, or WEIR, in inland navigation, all those works of wood or stone, or of both combined, fur the purpose of con fining and raising the water of a river.
The term lock, or pound-lock, more particularly denotes a contrivance, consisting of two gates, or two pairs of gates, called the lock-gates, and a chamber between them, in which the surfitce of the water may be made to coincide with that of the upper or lower canal, according as the upper or lower gates are opened ; by which means boats are raised or lowered from one level to another.