CHAPTER VI.THE BRAMAH LOCK.

Old French lockfig. 18.

fig. 18.

fig. 19. Old French lock.

The tumbler-principle, as we have said, is difficult to trace to its origin on account of the various aspects which it presents; but the great French treatise proves that the locksmiths of France were familiar with tumbler-locks a century ago. The plates of that work represent the details of numerous locks, on the upper edge of the bolts of which were notches calledencoches, as ato kfig. 18; into these notches sank asmall iron stud or stump called thearrêt du pêne, or bolt-stop, shewn infig. 19, attached to the upper portion of thegâchetteor tumbler, which, for the sake of economy of metal, is made in the form of a triangular spring in front of the boltk i; and not until the key, by its circular action, had raised this stud out of one or other of the notches, could the bolt move to the right or left. The stud was generally fixed to a spring which forced it down again into the notch as soon as the action of the key had ceased. Sometimes, however, the stud was fixed to the bolt, and the notches were in a separate tumbler orgâchette(seeE E,fig. 21); and in other instances, again, the stump was fixed to the case of the lock and caught into notches in the bolt. It will be seen, when we come to treat of tumbler-locks of later date, that there was much in these early locks to point out the way.Fig. 19, copied from the French work, represents a lock of the box or casket kind. Two staples, fixed into the cover, fall into two cavities or receptacles atCd; and a short bolt in each receptacle catches into each staple, one neargand one nearh. The small boltqis attached to the upper extremity of the leverq r s,fig. 19, and shewn separately infig. 20; and by the pressure of a springa(fig. 19) upon this lever, the boltqis kept locked in the staple. The vertical portion of this spring presses at its lower end on another springp(fig. 19) of singular curvature; and attached to the horizontal part of this second spring is the stud, which falls into a notch in the top of the bolt. The action of these parts, then, is as follows: when the key is placed upon the key-pin atZ, and turned round in the direction in which the hands of a watch move, the bitt presses against the tailsof the lever, moves it upon its centreZ,fig. 19,v,fig. 20, to the left, and consequently moves the upper partqto the right, drawing it out of the receptacle and liberating the staple withinC. Thus it will be seen that the leverq r s, held in one position by the springa, forms in itself a simple kind of spring catch-lock, and was, in fact, formerly used as such, without any other appendages except the staple in the lever, into which the catchqfitted on shutting down the lid. So also we may regard the other portion,fig. 18, ork i p h(fig. 19), as forming a separate lock; for the key after having passedScomes in contact with the triangular spring, which it raises thereby, lifting the stud out of the bolt, and exerting pressure against the barbs of the boltn.Fig. 18shoots the boltk, and also the short boltl, which passes through the staple in the cavityd,fig. 19.

Lever q r sfig. 20.

fig. 20.

The lock represented in the four following figures is also from M. de Réaumur’s chapter on locks in the work referred to. In this lock the tumbler-principle is carried out in a veryelaborate manner, for not only is the stump or studH(fig. 23) attached to a very strong spring (best shewn atH,fig. 22), which holds it with considerable force in one of the three notches of the principal boltR S(fig. 24); but there is also a second set of notchesE Ein thegâchetteG O(fig. 21), and a pin attached to one of the plates of the lock fits into one of these notches, thereby preventing the bolt from being moved until thegâchetteis lowered by the revolution of the key; so thatin attempting to pick this lock, not only must the springHbe raised so as to release the stud from the notches of the great bolt, but thegâchettemust be lowered to disengage the fixed pin from the notches. There is yet a third source of security. Attached to the large bolt are short projecting pinsF(fig. 21), against which an arm or detent,G F, of thegâchetteprojects, thus preventing the bolt from being shot back by any pressure applied to its extremityS.

fig. 21. Details of an old French lock.

fig. 22. Another view of the same.

fig. 23. Another view of the same.

fig. 24. The two bolts detached.

There are a few details relating to this remarkable lock, which may as well be introduced here in order to complete the description. The principal bolt can be shot twice, or bedouble-locked; hence it is furnished with three barbs for the key to act against, and with three notches for the spring-stud. The lower boltI Kcan be shot by the horizontal pressure of the buttonP(figs. 22,23), which is situated on the inner side of the door to which this lock is attached, so that a person inside the room can secure the door against any one on the outside who is not furnished with the proper key, for it must be remarked that the small bolt as well as the large one is acted on by the key. Now supposing the small bolt to be shot or locked, it is kept so by the pressure of the coiled springQ(figs. 21,22). But this small bolt is connected with the large one by means of the bent leverO N M(figs. 21,24), which turns on a pinNattached to the main bolt. Now, when both bolts are either fully shot or unshot, the armO Nlies flat against and parallel with the main bolt; but when the large bolt is unshot and the small one not moved, the armsO N,N M, fall into an inclined position, and the armO Npassing a little below the main bolt comes within the range of the web of the key, which in its revolution causes the bent lever to move upon its centreN, thereby restoringO Nto its horizontal position, and at the same time causing the armN Mto move from right to left, or in the direction for unshooting the small bolt; the end of this arm thus catches into a mortiseV(figs. 21,24) in the small bolt, and immediately unlocks it.

But to return to the subject of tumbler-locks. About theyear 1778, Mr. Barron introduced that species of double-action (as it may perhaps be termed) which so greatly increases the security of the simple tumbler,fig. 17. In the tumbler-locks previously made, if the tumbler were raised sufficiently high, the lock could be opened: there was no such possibility as raising ittoohigh; but Mr. Barron, by his invention, patented 31st October, 1778, rendered it absolutely necessary that a limit should be put to the height to which the tumbler should be raised, by rendering the bolt equally immovable whether the tumbler were too much or too little raised. Another important improvement was the introduction of two tumblers instead of one. The bolt has in its middle a slot or gating notched on both edges, the notches being fitted for the reception of studs fixed to the tumblers. Supposing the studs or stumps of the tumblers to be resting in the lower notches, they require to be elevated to the general level of the gating before the bolt can be moved; whereas, on the other hand, if the tumblers were raised ever so little too high, the studs will enter the upper notches, and prevent the shooting of the bolt. The lower edge, or belly, of each tumbler is acted on by the steps of the key during its circular movement; the leverage of the key being so exactly adjusted as to raise the tumbler to the desired height and no further. The tumblers are made unequally wide, so that steps or inequalities in the bit of the key are requisite to lift them both to the proper height. There are thus two improvements introduced: there are two tumblers instead of one, and each tumbler has a double instead of a single action.

This ingenious and very useful lock is represented, so far as regards its governing principle, infig. 25. The bolt is here seen to have a peculiar slot or hole cut in it, consisting of a narrow horizontal passage or gating, with three notches above it and three below it. These double notches might be available even for one tumbler only; but Barron used two or more for the sake of additional security. Infig. 25there are two tumblers shewn, expressed by dotted lines; both are hinged toone pivot, both are raised by the same action of the key, but the stump on the one tumbler does not coincide in position with that on the other. It will be seen that if the studs of the tumblers rested in the lower notches, they would require to be elevated to the level of the gating before the bolt could be moved; while, on the other hand, if lifted too high, the stumps would be caught in the upper notches, and would equally prevent the passage of the bolt, The tumblers are unequally wide; and the bitt of the key is stepped or notched in a corresponding way, that there may be one step fitted to act upon each tumbler. Mr. Barron also adopted the reverse arrangement of having the stump on the bolt, and the openings in the tumblers; so that the principle of his patent may be concisely expressed as being “an arrangement to allow a stump on the tumbler to pass through an opening in the bolt, or a stump on the bolt to pass through an opening in the tumbler.”

fig. 25. Action of Barron’s tumbler-lock.

A very elaborate tumbler-lock, patented 23d February, 1790, by Mr. Rowntree, contrasts remarkably with the simplicity of Barron’s lock. Mr. Rowntree’s lock consisted of tumblers combined with revolving discs or wheels. Its mechanism may be understood from the following description and engravings. The same letters refer to the same parts in the several figures.

Lockfig. 26.Lockfig. 28.Lockfig. 27.Lockfig. 29.Keyfig. 30.Details of Rowntree’s tumbler-lock.

Lockfig. 26.Lockfig. 28.

Lockfig. 26.

fig. 26.

Lockfig. 28.

fig. 28.

Lockfig. 27.Lockfig. 29.Keyfig. 30.

Lockfig. 27.

fig. 27.

Lockfig. 29.

fig. 29.

Keyfig. 30.

fig. 30.

Details of Rowntree’s tumbler-lock.

A Ais the plate which encloses the whole mechanism of the lock, and fastens it to the door;B Bis the bolt, guided in its motion by sliding under the bridgesC D;E Eare pillarswhich support a plate covering the works;Fare the circular wards surrounding the centre or key-pin; andashews the position of the key, which, in turning round, acts in a notchrin the bolt, and propels it;G, the tumbler, is a plate situated beneath the bolt, and moving on a centre-pin atd; it has a catch or stumpeprojecting upwards, which enters the notchessorgin the bolt, and thereby retains the latter for backward or forward motion, as the case may be;His a spring which presses the tumbler forward. The keya, in turning round, acts first against the partc cof the tumbler, and raises it so as to remove the stump from the notches; it can then enter the notchrin the bolt, and move it. So far there is no particular security; but Mr. Rowntree sought to obtain it by the following means. There is a piece of metalhfixed to the lower side of the tumbler, called thepin; when the tumbler is caught in either notch of the bolt, the pin applies itself to a cluster ofsmall wheelsI, fitted on one centre-pin beneath the tumbler; the edges of these wheels stop the pin, and prevent the tumbler from being raised. But each wheel has a notch cut in its circumferenceI; and it is only when the wheels are so placed that all their notches lie in a right line, that the pin can enter this compound notch and allow the tumbler to rise. The wheels must therefore be all adjusted to position; and this is effected by a number of leversKcentred on one pin atk; at the opposite end each lever has a toothmentering a notch in the wheel belonging to it; so that when any lever is pressed outward, it turns its wheel round. Now this pressure of the levers is brought about by a springnapplied to each; and when so pressed, the levers rest against a pinofixed in the plate. The key is so cut as to determine the extent to which the levers shall act upon the wheels. The key first operates from the curved partp pof the leversK, and raising them, turns all the wheelsIat once into the proper positions; in turning further round, it then operates on the partc cof the tumbler, causing the latter to rise and to release the bolt; and in turning still further round, it (the key) seizes the notchrof the bolt, and shoots it. The key is cut into steps of different lengths, as shewn atV V; each step operates on its respective leverKin a different degree from the others; the notch atsacts upon the tumbler, and the plain parttmoves the bolt.

We now proceed to notice the modern tumbler-lock. This was arranged by Bird, whose patent, bearing date 29th October, 1790, was for a series of four double-acting tumblers, differing in no respect from those patented by Barron, and closely resembling those in use at the present time in the best tumbler-locks. We will describe the modern tumbler-lock more particularly when we have gone through a few historical details on the subject.

Messrs. Mitchell and Lawton obtained a patent bearing date 7th March, 1815, for a lock in which were combined with the bolt and double-acting tumblers, a series of movable wards, and a revolving curtain for closing the key-hole. Theaction of the wards was peculiar. On introducing any key or instrument, and passing it round, a number of movable wards or pieces were thrown out so as to prevent the key from being turned back or withdrawn. It was necessary therefore to pass round the key so as to unlock the lock, and if that were not possible, as in the case of a false key being used, it was held permanently, and could only be released by destroying the lock, When the bolt was once shot, the wards were carried up so as to leave a clear passage for the key. This lock does not appear ever to have come into use, on account of the violence required in case a wrong key should be used either by accident or design.

The detention of a wrong key in this lock appears to have suggested the contrivance of adetector. This was first made by Ruxton, whose patent is dated 14th May, 1816. His detectors were of various kinds, the object of each kind being to give information to the owner in case any one of the tumblers should be overlifted in an attempt to pick the lock, which fact would be discovered on the next application of the true key. This is precisely the object of the detector in tumbler-locks at the present day, and Ruxton accomplished it by somewhat similar means. He also had a contrivance for holding a false key, as in Mitchell and Lawton’s lock; and he recommended this form of detector in the following words: “It is true that in this case the lock will have to be destroyed in order to open the door: the result is frightful; but we think the more terrible the result, the less likely would any one be to tamper with it.”

We now come to Chubb’s lock, patented 3d February, 1818, which consisted of double-acting tumblers and a peculiar kind of detector. This lock has been made the subject of various patents obtained in the years 1824, 1833, 1846, and 1847. This lock[4]consists of six separate and distinct double-actingtumblers, all of which must be raised to a particular height, neither more nor less, in order that the bolt may pass. It also comprises adetector, by which, should any one of the tumblers be lifted too high in an attempt to pick or open the lock by a false key, it would be immediately detected on the next application of the proper key. The tumblers are flat pieces of iron or steel, with the plane of the surface vertical, and pivoted at one end; and the following is the mode in which the key, the tumblers, and the bolt, are brought into mutual action.

[4]The lock about to be described is the latest and most complete form of Chubb lock up to the date of the Great Exhibition. The various additions and alterations which have been made in the lock since that date will be noticed in a subsequent chapter.

The bolt shoots in and out of the lock in the usual way. It has a square stud or stump riveted on one surface; and it is to furnish obstructions to the passage of this stud that the tumblers are provided. All the six tumblers are pivoted to one pin at the end, giving to each of them a small leverage, each independent of the others. There are six springs which press these tumblers downwards, one to each tumbler. There is a longitudinal slot or gating in each tumbler, large enough to receive the stud of the bolt; and unless all the six slots (supposing there to be six tumblers) coincide in height or position, the stud will not have a clear passage for moving to and fro. Now the slots are purposely made nearer the upper edge in some of the tumblers than in others, all the six being different in this respect; so that if they are all liftedequally, the slots do not coincide, and the bolt and its stud will not pass. The tumblers must then be raisedunequally, those to be most raised which have the slot nearest to the lower edge. To effect this, the bit of the key is cut into six steps or inequalities, each to act upon one particular tumbler, and each cut or stepped to the exact depth which will suffice for the proper raising of the tumbler. The key is inserted in the keyhole, and is turned; the six steps raise the six tumblers all to the proper height, to leave a clear passage along the slots; and the extreme end of the key then acts upon the bolt itself, and shoots it. To unlock it again, the same or a duplicate key must be used; for if another key be employed, differing by ever so little from the proper one, some one or more of the tumblers will be lifted either alittle too much or not quite enough; and in either case the stud of the bolt will catch above or below the slot, instead of having a clear line of movement along the slot itself. After both locking and unlocking, the springs force the tumblers down as far as they can go, burying the stud in the recesses above the slot; so that the tumblers must be raised by the key both for locking and unlocking.

The doctrine of chances has wide play in determining the relative position of the six tumblers. In Mr. Chubb’s essay this part of the subject is treated in the following way: “The number of changes which may be effected on the keys of a three-inch drawer-lock is 1 × 2 × 3 × 4 × 5 × 6 = 720, the number of different combinations which may be made on the six steps of unequal lengths (on a six-tumbler lock), 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; therefore 720 × 20 = 14,400 changes. The same process, after reducing the shortest step as much as possible, may be gone through with each of the other five steps; therefore 14,400 × 6 = 86,400, which is the number of changes that can be produced on the six steps. If, however, the seventh step, which throws the bolt, be taken into account, the reduction of it only ten times would give 86,400 × 10 = 864,000, as the number of changes on locks with the keys all of one size (that is, with one key of definite size in all save the lengths of the steps). Moreover, the drill pins of the locks and the pipes of the keys may be easily made of three different sizes; and the number of changes will then be 864,000 × 3 = 2,592,000, as the whole series of changes which may be gone through with this key. In smaller keys, the steps of which are capable of being reduced only ten times, and the bolt-step only five times, the number of combinations will be 720 × 10 × 6 × 5 × 3 = 648,000. On the other hand, in larger keys, the steps of which can be reduced thirty times, and the bolt-step twenty times, the total number of combinations will be 720 × 30 × 6 × 20 × 3 = 7,776,000.”

These enormous numbers have been the cause of much of the wonderment which the six-tumbler locks have excited; and, as we shall see further on, the Bramah lock presents still more of the marvellous in respect to this ringing of the changes.

fig. 31. Chubb lock, with detector and six tumblers.

The construction and action of the Chubb lock may be further illustrated by means of an engraving,fig. 31, in whichbis the bolt of the lock, with a stump riveted to it markeds. The six tumblers are shewn perspectively, the front or anterior one being markedt; they all move on the centre-pina, but are nevertheless perfectly distinct and separate, to allow of being elevated to different heights. Atdis shewn one end of a divided spring, the divisions being equal to the number of tumblers, one to each, and so bent that each spring may press upon its particular tumbler. Ateis the detector-spring, so placed that a projecting piece in the hindmost tumbler shall be near it; this tumbler having also fixed into it a stud or pinp. This being the arrangement, especially in relation to the stumpsand the tumblers, it follows that all the tumblers must be lifted to exact and regulated heights in order that the stump may pass through the longitudinal slits of the tumblers; unless it can do so, the bolt cannot be withdrawn. As there are gaps or notches in each tumbler bothabove and below the proper line of passage, and as there are no ordinary means of ascertaining when any one tumbler is lifted too high or not high enough, the safety of the lock is greatly increased by this uncertainty; especially when it is considered that this uncertainty is multiplied sixfold by the different modes in which the six tumblers are slotted. If, through the insertion of a false key, or by any other cause, any one of the tumblers be raised above its proper position, the detector springewill catch the hindmost tumbler, and retain it so as to prevent the bolt from passing; and thus, upon the next application of the true key, it will be instantly felt that some one of the tumblers has been overlifted, because the true key will not unlock it. To relieve the bolt from this temporary imprisonment, the key must be turned the reverse way, as for locking; all the tumblers will thus be brought to their proper position, and allow the stump to enter the notchesn n´; the bevelled part of the bolt will then lift up the detector-spring, and allow the hindmost tumbler to fall down into its proper place; and all this being effected, the lock may be opened and shut in the ordinary way. The pinpis so adjusted that if any one of the tumblers—front, back, or intermediate—be lifted too high, the pin will be lifted with it, and will catch into the detector-spring, thus producing the result just described.

fig. 32.Key to Chubb’s lock.

The key is represented infig. 32. It has six steps, besides a terminal step to act upon the bolt. The height of each step, or the distance to which it extends from the pipe of the key, depends of course on the height to which its corresponding tumbler is to be lifted; and it matters not whether the steps of the key are adjusted to the slots of the tumblers, or the slots to the steps, provided the agreement be brought about. It is simply a matter of manufacturing convenience that the key-steps are cut first and the tumbler-slots afterwards.We may here remark thatbit, orbitt, is the name given, somewhat indefinitely, either to the whole flat part of a key, or to the small stepped portions of it. The flat part was formerly termed thewebof the key, probably from thewebbedappearance of the keys to complex warded locks.

After the reading of Mr. Chubb’s paper before the Institution of Civil Engineers, Mr. Owen narrated one or two circumstances connected with the early history of Chubb’s lock. A convict on board one of the prison-ships at Portsmouth dockyard, who was by profession a lock-maker, and who had been employed in London in making and repairing locks for several years, and subsequently had been notorious for picking locks, asserted that he had picked with ease one of the best of Bramah’s locks, and that he could pick Chubb’s locks with equal facility. One of the latter was secured by the seals of the late Sir George Grey, the Commissioner, and some of the principal officers of the dockyard, and given to the convict, together with files and all the tools which he stated were necessary for preparing false instruments for the purpose, as also blank keys to fit the pin of the lock. A lock exactly the same in principle was placed in his hands, that he might examine it and make himself master of its construction. If he succeeded in opening the lock, he was to receive a free pardon from the Government, and a reward of 100l.from Messrs. Chubb. After trying for two or three months to pick the sealed lock—during which time, by his repeated efforts, he frequently over-lifted the detector, which was as often re-adjusted for his subsequent trials—he gave up the attempt. He stated that Chubb’s were the most secure locks he had ever met with, and that it was impossible for any man to pick or to open them with false instruments.

Mr. Owen further stated, that in order to compare the merits of Bramah’s and Chubb’s locks, he had suggested a mechanical contrivance, which was applied to one of Bramah’s six-spring padlocks belonging to the Excise. It was hungupon a nail, in a vertical position, secure from lateral oscillation. A self-acting apparatus was then applied, consisting of a pipe with hexagonal grooves, and a stud or bit corresponding with the division of the lock, and secured to it by a spring. In the grooves of this pipe small slides were inserted, which pressed against the spring keys of the lock; to these slides were attached levers, acted upon by eccentrics, moved by a combination of wheels, whose teeth differed in number so as to perform the permutation required for the different depths of the spring keys, corresponding with those of the proper key to the lock. The automaton machine was set in motion by a line working over a barrel, and acted upon by a weight; and was thus left acting upon the mechanism for a considerable time. At right angles to the pipe or false key was attached a rod and weight; and when the notches in the spring keys were brought in a line with the plane of the plate or diaphragm of the lock, the rod and weight turned the false key, opened the lock, and stopped the further motion of the automaton. In that state the slides indicated the exact depth of the grooves in the proper key, and gave the form of a matrix by which to make a key similar to the original one. The automaton worked during a period varying from half an hour to three hours, according to the state of permutation of the apparatus at the moment of being applied, compared with that of the slides in the lock. We confess that it is difficult to understand the action of this automaton from Mr. Owen’s description. We imagine that the false notches would effectually prevent the operation of the instrument, and openings would be required on each slide to bring it back, so as to meet the motions of the machine.

Mr. Owen did not state whether his apparatus had been successful with one only of Bramah’s locks or with several; nor did he describe any apparatus invented with the view to the picking of Chubb’s locks. He stated, however, that in order to ascertain the effect of friction on one of these last-named locks, it was subjected to the alternate rectilinear motion of a steam-engine in Portsmouth dockyard, and was lockedand unlocked upwards of 460,000 times consecutively, without any appreciable wear being indicated by a gauge applied to the levers and the key, both before and after this alternate action. Mr. Owen concluded by expressing his individual opinion that Chubb’s lock had never been picked. “The detector was the main feature of its excellence; and additional precaution, therefore, was only departing from its simplicity, and adding to the expense, without any commensurate advantage.”

In a subsequent chapter the degree of security afforded by various descriptions of locks, and the obstacles which they present of being picked, will come under notice; we therefore now proceed to describe briefly a few other tumbler-locks, or application of the tumbler-principle.

In Mr. Somerford’s lock, for which the Society of Arts gave a premium in 1818, an attempt was made to improve upon the ordinary action of tumblers. In most such locks, all the tumblers must ascend, although to different heights, before the stud of the bolt can pass through the slots; “which arrangement,” says Mr. Somerford, “gives an opportunity of introducing a nail, or a piece of stout wire, into the lock, and thus raising the tumblers without the necessity of using the key.” In his new lock, however, he made one lever to ascend while the other descended, by a somewhat complicated arrangement of slotted plates above and below the bolt. The key was so perforated as to be much endangered in respect to strength.

In Davis’s lock there is a double chamber with wards on the side of the key-hole. The key is inserted into the first chamber and turned a quarter round; it is then pushed forward into the inner chamber, where there is a rotating plate containing a series of small pins or studs, which are laid hold of by the key. By turning the key, the plate is moved round, the tumbler is raised, and the bolt is shot backwards and forwards. This lock, which is somewhat expensive, is used to some extent on Cabinet despatch-boxes.

The lock invented by Mr. Nettlefold is so constructed,that when the bolt is shot out by the key, two teeth or quadrants are projected from the sides of the bolt, which take a firm hold of the plate fixed on the door-post or edge. This construction is said to answer well for sliding-doors.

Mr. Alfred Ainger, in 1820, received a silver medal from the Society of Arts for a draw-back spring latch, in which the objects proposed were the two following—to render the lock more difficult of violation by a pick than those ordinarily in use; and to apply to it a key of which no ordinary person could take an impress, and which would be difficult of access even in a workman’s hand. The key is very peculiar; its pipe consists of three divisions, the section of the upper and lower divisions being circular, and that of the middle division triangular; the triangular portion is intended to give motion to some part of the interior of the lock during the rotation of the key. There are collars fixed on the extremity of the key, to act each on one tumbler; and there are modes, by varying the arrangement of these collars on an octagonal stem, to give something like a permutation to the number of variations to which the action of the key may be subject. The notches or slots are rather in the bolt than in the tumblers; and there are many peculiarities in the general arrangement.

In a lock invented and patented by Mr. Parsons, the tumblers are of a particular form, being hinged on a pivot at their centres, and working into and out of two notches cut in the under side of the bolt. It must be obvious that many variations in the adjustment of the tumblers of locks might be made, without vitiating the principle on which the action depends.

Many inventors have tried the use of an expanding web to the key, so planned that if the step of the web be long enough to reach the tumbler, it would be too long to pass through the key-hole; and therefore a principle of safety would operate by enabling the key to adjust itself at one moment to the size of the key-hole, and at another to the height of the tumbler. Mr. Machin of Wolverhampton invented such a key in 1827. The web of the key is movable on a countersunkpin, on which it can so far slide as to be drawn one-eighth of an inch from the barrel. The key-hole is of such a size as to admit the key only when the web is pressed close up to the barrel. When the key in this state is introduced, and is begun to be turned round, one of the notches in the web works into a raised circular edge of steel, placed eccentrically with regard to the lock-pin; so that as the key is turned, the web becomes drawn out, and is at its greatest elongation when it arrives at the tumblers: in the second half of its circular movement, the key becomes contracted to its original dimensions, and can then be removed from the lock.

Another mode of modifying the key has been introduced by Mr. Mackinnon, the object being to enable any person to change at will the pattern or arrangement of the movable parts of a lock and key; or to keep the key, when not actually in use, in such a state as to render it unavailing to any one but himself. It was a complex arrangement, which does not seem to have come much into use.

The lock invented by Mr. Williams, in 1839, may be designated a pin-lock, involving a principle analogous in many points to that of the Egyptian lock. This lock has a series of pins which reach through the cap, and are pressed to their places with a key like a comb or a rake-head. On the inner end of each pin is a flat piece of steel, in which is cut a notch for the passage of the bolt; but this passage is not clear until the notches in all the pieces of steel are in a right line. The pins are movable, and can be pushed either too far or not far enough to bring about the coincidence of position in the notches; and on this ground they are “double-acting.” Now the teeth of the key are of irregular lengths, each having a length just suited for pushing the pin to the proper depth: any other lengths of teeth would fail to open the lock. There is a mechanism of springs and levers to shoot the bolt when the pins in the plate are rightly adjusted. The arrangements in respect to the key are singular and somewhat awkward. The teeth which lock the bolt are not the same as thosewhich unlock it, the user having to change ends and adjust the bit to a socket-handle. This is one among many examples in which a lock embodies several principles, the inventor having set himself the task of combining the excellences of many diverse locks.

In respect to the tumbler-locks generally, the simplicity of action, the strength of construction, and the non-liability of disarrangement, have given them a high place among safety-locks. The only danger seemed to be, that any person once obtaining possession of the key could take an impression from it, and thence form a key which would command the lock. Attempts have been occasionally made to obviate this danger, by supplying the key with movable bits which could be changed at pleasure, so as to constitute any number of effectively different bits in succession. But the locks being so constructed that the bolt could only be moved when the tumblers were in a certain position, the owner was placed in this predicament: that it was useless to alter the arrangement of the bits in the key, unless the tumblers were altered in a corresponding manner; and this would entail the removal of the lock from the door, and the re-arrangement of the interior mechanism.

One of the great defects of tumbler-locks made previously to the last ten years was, that the tumblers, when lying at rest in the lock, presented at theirbelliesor lower edges precisely the same arrangement as the steps of the key. Indeed, in many locks of the present day, a good idea of the form of the key may be gained by feeling the bellies of the tumblers. The bellies are in fact cut out so as to compensate for the circular motion of the key, to allow them to remain at rest while the stump is passing through the gating. Even in tumbler-locks of the best construction the tumblers will vibrate more or less during the motion of the key; a defect which must be provided against in adjusting the lock, or the stump will be caught in its passage through the gating. Mr. Hobbs provides a simple remedy by enlarging the back part of thegating, the effect of which is as follows: when, in shooting back the bolt, as in unlocking, the key has got to its highest point, the stump enters the narrow end of the gating; but in shooting the bolt forward, as in locking, the stump enters the gating before the key has got to its highest point, and to allow for the slight vibratory motion of the tumblers during the passage of the stump, the gating is widened. The usual method of adjustment is to alter the forms of the bellies of the tumblers, thus greatly risking the security of the lock, a defect which was clearly perceived by Bramah [seepp. 67-70], and was one of the reasons which induced him to construct locks with slides instead of tumblers.

American locks on the tumbler-principle, and the relation which all such locks bear to the Bramah lock, will be better understood after the details of the following chapter.

The lock which was invented by the late Mr. Bramah deservedly occupies a high place among this class of contrivances. It differs very materially from all which has gone before it; its mechanical construction is accurate and beautiful; its key is remarkable for smallness of size; and the invention was introduced by the publication of an essay containing much sensible observation on locks generally. The full title of this essay runs thus: “A dissertation on the Construction of Locks. Containing, first, reasons and observations, demonstrating all locks which depend upon fixed wards to be erroneous in principle, and defective in point of security. Secondly, a specification of a lock, constructed on a new and infallible principle, which, possessing all the properties essential to security, willprevent the most ruinous consequences of house-robberies, and be a certain protection against thieves of all descriptions.” A second edition of thisDissertationwas published in 1815; but the work is now extremely scarce, and hardly attainable.

It is remarkable to observe the boldness and self-relying confidence with which Mr. Bramah, some sixty years ago, declared thatalllocks were, up to that time, violable; he felt that this was strictly true, and he hesitated not to give expression to his conviction. The following is from hisDissertation:—

“It is observable that those who are taken in the desperate occupation of house-breaking are always furnished with a number and variety of keys or other instruments adapted to the purpose of picking or opening locks; and it needs no argument to prove that these implements must be essential to the execution of their intentions. For unless they can secure access to the portable and most valuable part of the effects, which in most families are deposited under the imaginary security of locks, the plunder would seldom recompense the difficulty and hazard of the enterprise; and till some method of security be adopted by which such keys and instruments may be rendered useless, no effectual check or opposition can be given to the excessive and alarming practice of house-breaking.

“Being confident 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 dishonest 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. To demonstrate this bold and alarming proposition, I shall first state the common principleswhich are applied in the art of lock-making; and by describing their operation in instruments differently constructed, prove to my intelligent readers that the best-constructed locks are liable to be secretly opened with great facility; and that the locks in common use are calculated only to induce a false confidence in their effect, and to throw temptation to dishonesty in the way of those who are acquainted with their imperfections, and know their inefficacy to the purpose of security” (p. 5).

Tumblers had been so little thought of and used at the time Bramah wrote, that his attention was almost exclusively directed towardedlocks. The mysterious clefts in a key, connected with some kind of secret mechanism in the lock, had given the warded locks a great hold on the public mind, as models of puzzlement and security; and it was to shew that this confidence rested on a false basis, that he to a great extent laboured. The following is his exposition of the principle and the defects of the warded lock.

“Locks have been constructed, and are at present much used and held in great esteem, from which the picklock is effectually excluded; but the admission of false keys is an imperfection for which no locksmith has ever found a corrective; nor can this imperfection be remedied whilst the protection of the bolt is wholly confided to fixed wards. For if a lock of any given size be furnished with wards in as curious and complete a manner as it can be, those wards being necessarily expressed on what is termed by locksmiths the bit or web of the key, do not admit of a greater number of variations than can be expressed on that bit or web; when, therefore, as many locks have been completed of the given size as will include all the variations which the surface of the bit will contain, every future lock must be the counterpart of some former one, and the same key which opens the one will of course unlock the other. It hence follows that every lock which shall be fabricated on this given scale, beyond the number at which the capability of variation ends, must be as subject tothe key of some other lock as to its own; and both become less secure as their counterparts become more numerous. This objection is confirmed by a reference to the locks commonly fixed on drawers and bureaus, in which the variations are few, and these so frequently repeated, from the infinite demand for such locks, that, even if it were formed to resist the picklock, they would be liable to be opened by ten thousand correspondent keys. And the same observation applies in a greater or less degree to every lock in which the variations are not endless.

“But if the variation of locks in which the bolt is guarded only by fixed wards could be multiplied to infinity, they would afford no security against the efforts of an ingenious locksmith; for though an artful and judicious arrangement of the wards, or other impediments, may render the passage to the bolt so intricate and perplexed as to exclude every instrument but its proper key, a skilful workman having access to the entrance will be at no loss to fabricate a key which shall tally as perfectly with the wards as if the lock had been open to his inspection. And this operation may not only be performed to the highest degree of certainty and exactness, but is conducted likewise with the utmost ease. For the block or bit, which is intended to receive the impression of the wards, being fitted to the keyhole, and the shank of the key bored to a sufficient depth to receive the pipe, nothing remains but to cover the bit with a preparation which, by a gentle pressure against the introductory ward, may receive its impression, and thus furnish a certain direction for the application of the file. The block or bit being thus prepared with a tally to the first ward, gains admission to the second; and a repetition of the means by which the first impression was obtained, enables the workman to proceed, till by the dexterous use of his file he has effected a free passage to the bolt. And in this operation he is directed by an infallible guide; for, the pipe being a fixed centre on which the key revolves without any variation, and the wards being fixed likewise, their position must be accuratelydescribed on the surface of the bit which is prepared to receive their impression. The key therefore may be formed and perfectly fitted to the lock without any extraordinary degree of genius or mechanical skill. It is from hence evident that endless variations in the disposition of fixed wards are not alone sufficient to the purpose of perfect security. I do not mean to subtract from the merit of such inventions, nor to dispute their utility or importance. Every approach towards perfection in the art of lock-making may be productive of much good, and is at least deserving of commendation; for if no higher benefit were to result from it, than the rendering difficult or impossible to many that which is still practicable and easy to a few, it furnishes a material security against those from whom the greatest mischiefs and dangers are to be apprehended.”

There can be little doubt, in the present day, that Bramah did not over-rate the fallacies embodied in the system of wards for locks. He was sufficiently a machinist to detect the weak points in the ordinary locks; and, whatever may have been his over-estimate of his own lock (presently to be described), he was certainly guilty of no injustice to those who had preceded him; for their locks were substantially as he has described them. To understand the true bearings of his Dissertation too, we must remember that housebreaking had risen to a most daring height in London at the time he wrote (about the middle of the reign of George III.); and men’s minds were more than usually absorbed by considerations relating to their doors and locks.

Mr. Bramah, after doing due justice to the ingenuity of Barron’s lock, in which, if the tumbler be eitheroverlifted orunderlifted the lock cannot be opened, pointed out very clearly the defective principle which still governed the lock. “Greatly as the art is indebted to the ingenuity of Mr. Barron, he has not yet attained that point of excellence in the construction of his lock which is essential to perfect security. His improvement has greatly increased the difficulty but not precluded thepossibility of opening his lock by a key made and obtained as above described (by a wax impression on a blank key); for an impression of the tumblers may be taken by the same method, and the key be made to act upon them as accurately as it may be made to tally with the wards. Nor will the practicability of obtaining such a key be prevented, however complicated the principle or construction of the lock may be, whilst the disposition of its parts may be ascertained and their impression correctly taken from without. I apprehend the use of additional tumblers to have been applied by Mr. Barron as a remedy for this imperfection.” Mr. Bramah thought that Barron had a perception of a higher degree of security, but had failed to realise it; because, by giving a uniform motion to the tumblers, and presenting them with a face which tallies exactly with the key, they still partake in a very great degree of the nature of fixed wards, and the security of the lock is thereby rendered in a proportionate degree defective and liable to doubt.

To shew how this insecurity arises, Mr. Bramah illustrates the matter in the following way: “Suppose the key with which the workman is making his way to the bolt to have passed the wards, and to be in contact with the most prominent of the tumblers. The impression, which the slightest touch will leave on the key, will direct the application of the file till sufficient space is prepared to give it a free passage. This being accomplished, the key will of course bear upon the tumbler which is most remote; and being formed by this process to tally with the face which the tumblers present, will acquire as perfect a command of the lock as if it had been originally made for the purpose. And the key, being thus brought to a bearing on all the tumblers at once, the benefit arising from the increase of their number, if multiplied by fifty, must inevitably be lost; for, having but one motion, they act only with the effect of one instrument.”

It is worthy of notice, that even while thus shewing the weak points of the Barron lock, Mr. Bramah seems to havehad in his mind some conception of infallibility or inviolability attainable by the lock in question. After speaking of the defect arising from the bad arrangement of the tumblers, he says: “But nothing is more easy than to remove this objection, and to obtain perfect security from the application of Mr. Barron’s principle. If the tumblers, which project unequally and form a fixed tally to the key, were made to present a plane surface, it would require a separate and unequal motion to disengage them from the bolt; and consequently no impression could be obtained from without that would give any idea of their positions with respect to each other, or be of any use even to the most skilful and experienced workman in the formation of a false key. The correction of this defect would rescue the principle of Mr. Barron’s lock, as far as I am capable of judging, from every imputation of error or imperfection; and, as long as it could be kept unimpaired, would be a perfect security. But the tumblers, on which its security depends, being of slight substance, exposed to perpetual friction—as well from the application of the key as from their own proper motion—and their office being such as to render the most trifling loss of metal fatal to their operation, they would need a further exertion of Mr. Barron’s ingenuity to make them durable.”

It may perhaps be doubted whether the principle of Bramah’s lock is not more clearly shewn in the original constructed by him than in that of later date. In appearance it is totally different, but the same pervading principle is observable in both; and the cylinder lock can certainly be better understood when this original flat lock has been studied. The annexedwoodcutis taken from the first and very scarce edition of Mr. Bramah’sDissertation; the description is somewhat more condensed, but perhaps sufficient for the purpose.

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