LOCK. An instrument composed of springs and bolts, used to fasten doors, drawers, chests, &e. It is an improve ment on the primitive latch or bolt, with a crooked stick or instrument, to turn it through a hole on the outside. Obsta cles are opposed inside, and then the ac commodating the key to pass them, con stitutes its wards, the object being merely to turn and unturn a bolt, now called locking and unlocking. On the number and complication of the obstacles in car riyng the key to the bolt, so as to turn it, depends the perfection of the lock. The spring-lock consists of the main plate, the cover-plate, and the pin-hole. In, and on the main plate, is the key-hole, the top-hook, the cross-wards, the bolt knob, the tumbler and its pin, and the staples. To the cover-plate Is affixed the main, cross, and step-wards, and the pin. With the pin-hole are connected the hook, cross, and bow-wards, and the bit.
A good lock is the master-piece in smithery, and requires much art and deli cacy in contriving and varying the wards, springs, bolts, and other parts whereof it is composed, so as to adjust them to the plates where they are serviceable, and to the various occasions of their use. The structure of locks is so varied, and the number of inventions of different sorts so extended, that we cannot attempt to enumerate them. Those placed on outer doors are called stock locks, those on chamber door spring locks, and such as are hidden in the thickness of the doors to which they are applied are called mor tise locks. The padlock is too well known to need description. We here add the conditions which, to Mr. Nicholson, ap pear necessary in a lock of the most per fect kind : 1. That certain parts of the
lock should be variable in position through a great number of combinations, one only of which shall allow the lock to be opened or shut. 2. That this last mentioned com bination should be variable at the pleas ure of the possessor. 3. That it should not be possible, after the lock is closed and the combination disturbed, for any one, not even the maker of the lock, to dis cover, by any examination, what may be the proper situations of the parts required to open the lock. 4. That trials of this kind shall not be capable of injuring the works. 5. That it shall require no key ; 6. And be as easily opened in the dark as in the light. 7. That the opening and shutting should be done by a process as simple as that of a common lock. 8. That it should open without a key, or with one, at pleasure. D. That the key hole be concealed, defended, or inaccessi ble. 10. That they may be used by a stranger, without his knowing or being Able to discover the adopted combination. 11. That the key be capable of adjust ment to all the variations of the lock, and yet be simple. 12. That the lock should not be liable to be taken off and examined, whether the receptacle be open or shut, except by one who knows the adopted combination. These considera tions involve a mechanical problem of great difficulty ; but much towards its accomplishment has been effected in va rious inventions that have been promul gated, and more especially in those of Bramah, Chubb, Taylor, &c.