Lock

Well known contrivance to secure a door, lid or other object. The ancients do not seem to have been succe ful in locks; those of the Egyptians, Greeks and Romans being clumsy. The difficulty to be overcome in lock-making is to construct it so that it cannot be opened except by its own key nor admit of being picked. Therefore the interior of the lock is provided with wards and the key with clefts corresponding to them; no key can pa unle it has the proper clefts. Locks of a better kind have tumblers instead of wards; the tumblers being hinged pieces of metal within the lock which must be moved or raised before the key can act upon the bolt. The letter lock or combination lock has usually a number of rings placed with their plane surfaces in contact; every ring revolves on an axis; and the lock cannot be opened until all the rings are brought into exactly defined positions. Locks are also connected with clock work, so that they cannot be opened until a certain hour.