= 



LOCK. 



c hat, even oupporicg a person to obtain a correct impression of the 

 hole*, it would be diffi.-ult to ascertain the exact length necessary for 

 the pin* of the key. 



withstanding the high antiquity of the tumbler principle, its 

 first important application in this country appears to have been made 

 by Ban-on, in 1774. In the simple ionn of the tumbler represented 

 in Pig. 8, there U 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 U remedied in Barren's lock, 

 by the use of several tumblers, each of which requires to be raised to 

 a different degree, and any one of which, if lifted too high, win form 

 as effectual a barrier to the motion of the bolt as if it were not lifted 

 at alL To illustrate this, let a, Fly. 10, represent a tumbler pivoted at 

 b, pressed downwards by the action of a spring at t, but having its 

 downward motion limited by the contact of the tail d with a fixed pin. 

 Behind the tumbler lies the boh; and at e an opening, somewhat 

 resembling the letter H in shape, is cot through the tumbler, to allow 

 a prominent square stud, which is attached to the bob, to pass through 



Fig. 10. 



Fig. 11. 



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 th-- horizontal 

 portion of the aperture opposite to the stud, so that the stud, which 

 fits it accurately, may slip through it. Fig. 11 shows the tumbler 

 raised to this position, and the bolt half shot. When fully shot the 

 tumbler again falls ; the stud is secured in that notch of the aperture 

 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 r/vot. Fiy. 12 represents the bit of a key adapted for a lock with 



Kg. li. 



three tumbler*. 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 dugim* of projection. In the event of such a key being 

 suspected to have fallen into wrong hands, the tumblers might be 

 taken oat and returned on to their common axis in a new order, so as 

 to require a key in which the parts, a, &, c. and d, will stand in a 

 different relation to each other, by which means the old key will be 

 rendered useless. 



In many ingenious locks of this character the same object is attained 

 by the ue of solid tumblers, carrying studs which paaa through open- 

 ing* in the bolt. In a lock of this description invented by Mr. Somer- 

 forJ, one of the tumblers is drawn downwards by the key while the 

 others are raised, thus introducing a new complication which greatly 

 inereaaec the difficulty of picking, without adding materially to the 

 east of the kick. 



Chubb'* detector lock, the original patent for which was obtained in 

 4 one of the most celebrated locks made on the principle above 

 described. Its peculiar merit consists in the addition of a lever, called 

 the dttxtor, which is so fixed that, while it does not affect the bolt 

 under ordinary circumstances, it cannot fail to move so as to drop a 

 catch into the bolt if any one of the tumblers be lifted a little too high, 

 as some of them must inevitably be by any attempt at picking. By 

 thus fixing the bolt immoveabry, it not only readers useless any further 

 attempt at picking the lock, but also gives notice of the attempt which 

 has been made, when the proper key is next applied. 



In Bramah's lock, which was invented and patented about 1784, the 

 principle of tumblers is applied in a very different manner to that 

 above described, and the use of ward* U entirely abandoned. The 

 ordinary mode of shooting the b ..It , by the action of the bit of tLe 

 key, is abandoned ; the office of the end of the bit being performed by 

 a stud attached to the end of a cylindrical barrel mounted in the lock, 

 and which contains all its eaential parts. Fij. IS represents this 

 barrel, of the actual size, drawn from a street-door latch-lock. In this 

 cat a represents the stad by which, when the barrel is caused to re- 

 volve on its axis, the bolt is moved as by the bit of an ordinary key. 

 This revolving motion is imparted to the barrel by the insertion of the 



AT A*D SCI DIV. TOT. T. 



LOCK. siz 



| proper key, which is represented in Pig. 16, and whkif 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 cut into two halves by a division shown in 



Fig. 14. 



the cut at top and bottom, and is inserted, by its inner edge, in the slit 

 or opening i 6 in the barrel. The four notches in the inner edge of the 

 plate are thu< placed upon the edg a 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, fiy. 15 is a longitudinal section of the barrel with the 



Fig. IS. 



:-... . 



end of the key as applied to bring the sliders into the required position 

 for allowing the barrel to turn ; and Fin. !<" represents, at a in pro 

 file, and at 6 in an end view, the key itself separately. The seven. 

 figure.!, aided by the foregoing description, will show the mode in which" 

 this ingenious lock acts. The whole of the apparatus is securely 

 enclosed in a turned brass box, so that even the ends of the sliders are 

 only visible at the farther extremity of the deep and very small key- 

 hole. To prevent the sliders from working too loose, or from dropping 

 too far into the barrel, they are made of a thin piece at metal doubled, 

 av ^^p" B> at f t Fig. 16 1 so that their *""*' ** w ^*, having an inclination to 

 spring open, press with sufficient force against the siies of the grooves 

 in which they slide to keep them in position until the pressure of the 

 key is withdrawn and they are expose 1 to the counter pressure of thi 

 helical spring. The two additional small notches represented in the 

 tumblers of fiy. 15 and 16, add greatly to the security of this kind of 

 lock. 



The variety attainable in the arrangement of locks on this principla 

 forms one of its great recommendations. Our illustrations refer to one 



of its sunniest forms ; but even in this form the variety , 



without any difference in the size of the key.is very great. By the use, 

 however, of more sliders, the number of different locks, each of which 

 may have the same external appearance, but can be opened only by its 

 own proper key, is increased almost to infinity. Bramih showed that 

 if twelve sliders were employed, the number of changes which might be 

 produced by simply varying their relative positions would amount to 

 479,001,500 ; while by adding one more slider the number would be 

 increased to 0427,019^00. In the event of a key being lost, or the 

 owner desiring to have a lock altered, it is possible to change the 

 lulstim positions of the sliders, so as to render tits old key tmlras 

 Mcutfr-l-ryi may also be nud-a by constructing a suit of locks alike In 

 everything but the position of their notches, and then applying to each 

 of them in iiiocnsioii the master-key, which must have notches differ- 



