Lock, a well-known contrivance for fastening doors, chests, or the likc ; and which is generally opened with a key.

From the different structure of locks, adapted to various purposes, they acquire different names.-Those fixed on outer doors, are called stop-locks ; those on chamber-doors, spring-locks ; and such as are affixed to trunks, are known by the name of padlocks, trunk-locks, etc,-Of these, the spring-lock is the principal, both on account of its more general utility, and for the curious intricacy of its structure. Its chief constituent parts are, the main-plate; cover-plate ; and pin-hole: to the first belong the key-hole, top-hook, cross-wards, bolt-toe, or bolt-knab, draw-back spring-tumbler, pin of the tumbler, and staples.-With the cover-plate are connect ed a pin, main-ward, cross-ward, and step-ward or dap-ward: lastly, the pin-hole corresponds with the book-ward, main-cross-ward, shank, pot or beard, bow-ward and bit.

The excellence of locks consists in the security they afford ; 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 its without proper key, has ever been an object of considerable importance.

In the year 1784, the Society for the Encouragement of Arts, etc. conferred their silver medal on Mr. Taylor, of Petworth, for his improvement on the latch or spring-bolts of common locks. This is effected by simply reversing the tumbler, so that its curved side acts against two stubs fixed on the tail of the latch, and thrusts back the latter with ease ; whether the knob be turned to the right or to the left, when the lock is opened. Mr. Taylor has also, behind the tail of the latch, fixed a guide containing a groove, in which runs a small friclion-ivlieel, that serves to keep the latch in its direct situation, and at the same time to diminish its friction : the arms of his tumbler are somewhat contracted, in order that the latch or spring-bolt may move with greater facility. By this construction, the parts of the tumbler and latch, which are in contact, move in a line, so that they pass over the greatest space, under the smallest angle ; and the lock itself may be constantly used for several years, without requiring the application of oil. The same Society also granted, in the same year, the sum of ten guineas to Mr. Marshal, for a secret escutcheon, which, when fixed to a lock, may be so repeatedly varied, that even the artist who made it, is unable to open the lock : as, however, a satisfactory description of its mechanism cannot be given, without the aid of engravings, we refer the reader to the 3d vol. of the Society's Transac-. tions.

Various patents have been obtain--ed for the construction of locks, so as to prevent the possibility of picking them : the principal of these is Mr. Bramah's, registered in 1784 ; and Mr. Spears's, in 1795 ; but, as the account of those inventions would be unintelligible without the aid of several engravings, the curi-ous reader will consult the 5th and 8th vols, of the Repertory of Arts and Manufactures, where they are minutely specified.

Lock, in inland navigation, de-notes all such works (whether of wood or stone) which are intended to raise the water of a river; but it is more particularly applied to a kind of canal inclosed between two gates, the upper of which; is called a sluice-gate, and the lower a flood-gate. These serve to confine the water, and thus to facilitate the passage of boats, both in ascending and descending the canal.

In the year 1791. a patent was granted to Mr. James Playfair, architect, for his method of constructing the locks of navigable ca-nals on a new principle, and also for improving such as are already erected. With this design, a certain portion of water, in the ascent and descent of vessels, is conducted into reservoirs or cisterns communicating with the lock upon diffe rent levels, and thus eventually saved ; because their apertures may be opened and closed at pleasure, so that only the sixth part is required for the passage of boats. The particulars of this ingenious contrivance are inserted, and illustrated with engravings, in the 3d vol. of the Repertory of Arts, etc.

Another patent was granted, in 1798, to Mr. James Fussell, for his invention of a machine or balance-lock, serving to raise or lower boats on canals ; an account of which appeared in the 11th vol. of the work before quoted.

Lock. - In June, 180i, a patent was granted to Mr. Holem-berg, for his invention of locks or fastenings adapted for general use, on a new and improved construction. - The external form of the locks, thus manufactured, corresponds with those in common use : internally, however, an orbicular bolt is substituted for a rectilineal one, the security of which is increased by an inside tumbler that is fastened by a flat spring bolt. The whole manufacture of this lock is remarkable for its simplicity and ingenuity, with which it com-bines the important advantage of security; so that this contrivance justly merits the preference.