CONSTRUCTION OF LOCKS AND KEYS.
that the bottom tumbler has a tooth near the detector-spring. G is a stud, or pin fixed into, and forming part of the bottom tumbler, and H is the key. Now it will be obvious, that the whole of the tumblers must be lifted precisely to the different heights required, to allow the square stud B to Pass through the longitudinal slots of the tumblers, so that the bolt may be withdrawn. There is no means of telling when any one tumbler is lifted too high, or not high enough, much less can the combination of the six be ascertained ; and if a false key should be inserted, and any one of the tumblers should be raised beyond its proper position, the detector-spring F, will catch the bottom tumbler C, and retain it, so as to prevent the bolt from passing; and thus, upon the next application of the true key, immediate notice will be given of an attempt having been made to pick the lock, as the true key will not then at once unlock it. By turning the key, however, the reverse way, as in locking, the tumblers will be brought to their proper bearing, allowing the bolt to move forward, and the stud B to enter into the notches |. The bevelled part of the bolt A will then lift up the detector-spring F, and allow the bottom tumbler C to fall into its place. The lock being now restored to its original position, may be opened and shut in the ordinary manner. It will be seen, that when the lock is detected, nothing but its own key can restore it to its former condition.
Fig. 6. CHUBB'S LOCK.
The following calculation will show the number of changes which may be made in the combinations of Chubb's locks ; the same principle will, of course, apply to any other locks, having a number of moveable tumblers, or sliders.
The number of changes which may be effected on the keys of a three-inch drawer lock, L, is 1 x 2 x 3 x 4 x 5 x 6 = 720, the