140 LOCKS 



here that the action of the key is to raise the tumbler, so that the bolt has free 

 motion : this action will be intelligible by tracing the action of the, key on the dotted 



lines. These tumbler-lqcks are greatly varied in 

 character ; but in principle they are as above 

 described. 

 Numerous well-known locks have been pa- 



II - - ,. I. tented, the most remarkable being Chubb's 



o;.?__I 1 lock, which has been fully described by the 



' 1| :1' ; 4"K.': II I inventors in a paper read before the Institu- 



tion of Civil Engineers ; and also in an excel- 

 lent treatise on locks to be found in Mr. Weale's 

 series of useful manuals. This lock is essen- 

 tially a tumbler-lock, it being fitted up with 

 no less than six tumblers ; and the key has to 

 raise, by a series of steps, these before the bolt 

 is free to move. It will be obvious, that unless 

 the key is exactly fitted to move these, there is no chance of moving the bolt. In this 

 paper already alluded to Mr. Chubb says : 



' The number of changes which may be effected on the keys of a three-inch 

 drawer-lock is 1x2x3x4x5x6 = 720, the number of different combinations 

 which may be made on the six steps of unequal lengths without altering the length of 

 either step.' The height of the shortest step is however capable of being reduced, 20 

 times ; and each time of being reduced, the 720 combinations may be repeated ; there- 

 fore 720x20 = 14,400 changes.' By effecting changes of this character, therefore, 

 almost any number of combinations can be produced. The Bramah lock has been long 

 celebrated, and most deservedly so. Notwithstanding the fact that this lock was picked 

 by Mr. Hobbs after having the lock in his possession for sixteen days, it appears to us 

 that it most fully justifies the boast made by Mr. Bramah in his ' Dissertation on the 

 Construction of Locks.' ' Being confident,' he says, ' that I have contrived a security 

 which no instrument but its proper key can reach, and which may be so applied as 

 not only to defy the art and ingenuity of the most skilful workman, but to render the 

 utmost force ineffectual, and thereby to secure what is most valued as well from dis- 

 honest servants as from the midnight ruffian, I think myself at liberty to declare (what 

 nothing but the discovery of an infallible remedy would justify my disclosing) that all 

 dependence on the inviolable security of locks, even of those which are constructed on 

 the best principle of any in general use, is fallacious.' Ho then proceeds to demonstrate 

 the imperfections of ordinary locks, and to describe his own. 



' The body of a Bramah lock may be considered as formed of two concentric brass 

 barrels, the outer one fixed, and the inner rotating within it. The inner barrel has 

 a projecting stud, which, while the barrel is rotating, comes in contact with the bolt 

 in such a way as to shoot or lock it ; and thus the stud serves the same purpose as 

 the bit of an ordinary key, rendering the construction of a bit to the Bramah key 

 unnecessary. If the barrel can be made to rotate to the right or left, the bolt can bo 

 locked or unlocked, and the problem is, therefore, how to insure the rotation of the 

 barrel. The key, which has a pipe or hollow shaft, is inserted in the keyhole upon 

 the pin, and is then turned round; but there must be a nice adjustment of the me- 

 chanism of the barrel before this turning round of the key and the barrel can be in- 

 sured. The barrel has an external groove at right angles to the axis, penetrating to 

 a certain depth ; and it has also several internal longitudinal grooves from end to 

 end. In these internal grooves thin pieces of steel are able to slide, in a direction 

 parallel with the axis of the barrel. A thin plate of steel, called the locking plate, is 

 screwed in two portions to the outer barrel, concentric with the inner barrel ; and at 

 the same time occupying the external circular groove of the inner barrel ; this plate 

 has notches, fitted in number and size to receive the edges of the slides which work in 

 the internal longitudinal grooves of the barrel. If this were all, the barrel could not 

 revolve, because the slides are catching in the grooves of the locking plate ; but each 

 slide has also a groove, corresponding in depth to the extent of this entanglement ; and 

 if this groove be brought to the piano of the locking plate, the barrel can be turned, 

 so far as respects the individual slide. All the slides must, however, be so adjusted, 

 that their grooves shall come to the same plane ; but, as the notch is cut at different 

 points in the lengths of the several slides, the slides have to be pushed in to different 

 distances in the barrel, in order that this juxtaposition of notches may be insured. 

 This is effected by the key, which has notches or clefts at the end of the pipe equal in 

 number to the slides, and made to fit the ends of the slides when the key is in- 

 serted ; the key presses each slide, and pushes it so far ns the depth of its cleft will 

 permit ; and all these depths are' such that all the slides are pushed to the exact 

 position where their notches all lie in the same plane ; this is the plane of the locking 



