The principle of security by tumblers has been known to the Egyptians from a very remote period. In the lock now commonly used in Egypt and Turkey, the bolt is secured by a number of pine, which fall into holes in the bolt when it is shot. In the annexed diagram, a is a part of the bolt, capable of eliding through the solid Our remaining illustrations of warded keys are intended to the theory of master keys. In Fig. 6, the wards of the keys o, p, and q are so far different from each other that neither of those three keys would open the lock designed for either of the ether two ; but a key formed like r would readily open any of the locks of the other three.
One defect of warded locks is that. complicated they may be, an ingenious picker will mostly be able to detect their form and piece b, in which are a number of hollows, c, c, c, each• containing a moveable pin. If the bolt be slid forward until the boles d, d, d, come under the pins c, c, c, the lower ends of the pins will drop into them, and the bolt will consequently be held fast. It can only be released by the application of a key which has a series of pins exactly corre sponding with the holes in the bolt, and which, being introduced into the bolt is pressed upwards to lift the pins clear of it. The security arises from the concealment of the obstacles, and from the circumstance that, even supposing a person to obtain a correct impression of the holes, it would be difficult to ascertain the exact length necessary for the pins of the key.
Notwithstanding the high antiquity of the tumbler principle. its first important application in this country appears to hare been made by Barron, in 1774. In the simple form of the tumbler represented in Fig. 8, there is the disadvantage that, while it effectually prevents the removal of the bolt unless the tumbler be raised high enough, it presents no obstacle to its removal when the tumbler is thrown up beyond the proper degree. The defect is remedied in Barron's lock, by the use of several tumblers, each of which resnires to be raised to a different degree. and any one of which, if lifted too high, will form as effectual a barrier to the motion of the bolt as if it were not lifted at all. To illustrate this. let a, Fig. 10, represent a tumbler pivoted at b, pressed downwards by the action of a spring at c, but having its downward motion limited by the contact of the tail d with a fixed pin. Behind the tumbler lies the bolt; and at e an opening, somewhat resembling the letter H in shape, is cut through the tumbler, to allow a prominent s ware stud, which is attached to the bolt, to pass through proper key, which is represented in Fig. 16, and which' has a very
small bit adapted to the square notch at the bottom of the key-hole shown in the front end of the barrel; but the barrel is prevented from revolving, excepting when the proper key is applied, by a peculiar con trivance. The barrel, which contains four sliders radiating from its centre or axis, has a motion in the direction of its length ; the sliders are continually pressed forward to the front or key-hole end of the barrel by a helical spring ; and there is a circular plate of steel, repre sented in Fig. 14, which is cat into two halves by a division shown in it The bolt secured by such a tumbler can only be shot when the tumbler is raised precisely to such a degree as to bring the horizontal portion of the aperture opposite to the stud, so that the stud, which fits it accurately, may slip;hrongh it. Fig. 11 shows the tumbler raised to this position, and the half shot. When fully shot the tumbler again falls; the stud is secured in that notch of the apeiture which lies nearest the end of the tumbler ; and an equal security is afforded against any attempt to return it to its first position by any key which does not lift it precisely to the proper height. Several such tumblers may be placed in one lock, the whole being mounted upon one pivot. F;o. 11 represents the bit of a key adapted for a lock with the cut at top and bottom, and is inserted, by its inner edge, in the slit or opening b b in the barrel. The four notches in the inner edge of the plate are thus placed upon the edge of the four sliders in the barrel ; and the barrel cannot be turned round unless the four sliders are so far pushed in by the key that their notches may all tally with the edge of the plate. Fig. 15 is a loneitudinal section of the barrel with the three tumblers. The lock to which this key is adapted is guarded by two wards ; and the end of the bit is divided into four portions, of various degrees of projection. In the event of such a key being suspected to have fallen into wrong hands, the tumblers might be taken out and returned on to their common axis in a new order, so as to require a key in which the putt a, b, e. and d, will stand in a different relation to each other, by which means the old key will be rendered useless.