SI* 



-:. 



The keys most, of course, be cot of a corresponding fonn, by which 

 the difiruhy of imrtn* ; ~ * P*** 1 ? '"'""id 



<m At use"of wards, may be readily 

 of the intern ariM* fa- 





j - f 



. _ sjstuii ariMt from the circumstance that, 

 we*. it U not absolutely necessary Uut a surreptitious 

 ____ -bould P-fatly thread the maw. of the warda^ But 

 while the ward, afford scanty against ordinary keys, they afford none 



against a pit* or 



nty against ordinary k, 



afafatai try like i, Pig. 3, which would open 



. J. 



an of the locks suited for 9, *, and i, the only part essential to the 

 Boring of the bolt being the extremity of the bit, which is retained in 

 the skeleton key with nothing but a slender piece to connect it with 

 toe pipe or shank. The security may be greatly increased by the use 

 of other wards, attached to the opposite plate of the lock, and requiring 

 atrtthf m that part of the bit of the key which is represented by the 

 t y r *W connecting piece in the skeleton I. Such is the case in all the 

 keys represented in Fig*. 4, 5, and 6. In Pig. 4, I represents a key for 



r\f. t. 



a solid-warded lock, which might, however, be easily picked by a 

 skeleton key resembling r, Pig. 6. The greater complication of the 

 wards in m. Pig. 4, increases the difficulty of picking; while by the 

 adoption of the arrangement shown at n, Pig. 4, the difficulty of intro- 

 ducing; a false key is made perhaps a great as possible, since no instru- 

 ment that does not thread all the intricacies of the wards could answer 

 the purpose. All the keys hitherto represented, as well as those in 

 Pty. 6, are pipe-keys, adapted for such locks as have a fixed pin or axis, 

 and can only be opened from one side. It is, therefore, of no conse- 

 quence that the wards attached to the back and front plates of the 

 lock should resemble each other. In ordinary door-locks, however, in 

 which the key may have to be inserted from either side, it is essential 

 that the wards attached to the two plates, if such be used, should 

 either be precisely similar, or should bear such a relation to each other 

 that notches may be cut in both sides, or rather edges of the bit, to 

 suit both sets of wards; it being a necessary condition that the two 

 ides of the bit, marked a and 6 in the cut, Pig. 5, should be perfectly 



n*. 5. 



alike. Our remaining illustrations of warded keys are intended to 

 explain the theory of master keys. In Pig. 6, the wards of the keys o, p, 



and V are so far different from each other that neither of those three 

 keys would open the lock designed for either of the uther two; 

 but s key formed like r would readily open any of the locks of the 

 other three. 



One defect of warded locks is that, however complicated they may 

 be, an insjanlnin picker will moetly be able to detect their form and 



LOCK. MO 



position, by inserting a blank key with the bit covered with wax or 

 tallow, so a* to receive an inn>minn of the concealed obstructions in 

 the lock. It is a very common practice to cut more notches in the key 

 than there are wards in the lock ; so that the complex appearance of a 

 " y is no certain proof of the secure construction of the lock to which 

 it belongs. Some contrivance is necessary to keep the bolt steadily in 

 the position in which it is left by the key ; and in locks which depend 

 upon wards for their security, this is usually effected by means of a 

 spring, as illustrated by Piy. 7. which represents the interior of a small 

 cupboard lock, with the bolt a d 6 kalf dot, or in a position inter- 

 mediate between locking and unlocking, and capable of being moved 

 either backwards or forwards by the action of the bit of the key at e 

 in a curved hollow formed in the lower edge of the bolt. The neces- 

 sary raising of the bolt and Kmijinasinii of the spring are properly 



rig. i. 



nt.. 



effected by the action of the key ; but as they may also be effected by 

 pressure upon the end of the bolt, the security of locks in which such 

 an arrangement is adopted, which are called lack-tiiring locks, is much 

 impaired. 



Tumbler Lock*. We pass to the explanation of the second principle 

 of security : that which consists in the use of moveable impedimenta 

 to the motion of the bolt. Pit. 8 represents a lock provided with a 

 common tumbler. In this figure the bolt a, b, though shot backwards 

 and forwards, has no spring or notches to catch on the back rim of the 

 lock, to hold it in any required position ; but it is provided with two 

 notches in its upper edge, at c and rf. Behind the bolt is a piece of 

 metal called the tumbler, pivoted to the plate of the lock at /, and con- 

 tinually forced downwards by a spring which presses upon its upper 

 edge. Near the end e, the tumbler carries a projecting stud, which, 

 when the bolt is fully shot, falls into the notch rf, and holds it firmly 

 until, by the application of the key, the tumbler ia lifted up to the 

 position shown in the cut ; by this action the bolt is released, so that 

 the further turning of the key shoots it back, when the stud of the 

 tumbler falls into the notch e, and again secures the bolt. So long as 

 the tumbler remains in its proper notch, the bolt cannot be moved 

 backwards or forwards by any pressure upon its ends ; and the lock 

 cannot be opened by any false key unless its bit be so formed as to 

 reach the tumbler as well as the bolt. To render this more difficult 

 the tumbler is often made to fall a little lower than the bolt, so an to 

 be acted upon by a tttp formed on the bit of the key ; while further 

 security may be obtained by the use of two or more tumbler*, which 

 may be acted upon by different steps on the key. The great exactness 

 requisite in the length of the bit forms a strong recommendation of 

 even the commonest tumbler locks ; for if the bit be ever so little too 

 short it will not lift the tumbler out of its notch, while if it be but a 

 very little too long, it will not enter the curved portion of the bolt. 



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 pins, 

 which fall into holes in the bolt when it is shot. In the annexed 

 diagram, a is a part of the bolt, capable of sliding through the solid 



Fig. 9. 



piece 6, in which are a number of hollows, r, t, e, each containing a 

 moveable pin. If the bolt be slid forward until the holes d, d, d, come 

 under the pins c, e, 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 i* prtsstd upwards to lift the pins clear of it The security 

 arises from the concealment of the obstacles, and from the circumstance 



