[12]By J. Beverley Fenby, Mechanical Engineer, of Birmingham. Extracted chiefly from the Proceedings of the Institution of Mechanical Engineers, 1866.
[12]By J. Beverley Fenby, Mechanical Engineer, of Birmingham. Extracted chiefly from the Proceedings of the Institution of Mechanical Engineers, 1866.
The simplefixed-guardorwardedlock is so utterly worthless for security, no matter what amount of good workmanship be bestowed upon it, that it demands but short notice. It was contrived with the intention of making the passage to the bolt intricate; but it will be seen at once that this intricacy does not really offer any security. The wards of a lock are circular arcs of thin metal, so arranged as to require a key of peculiar pattern to pass amongst them, the shape of the cuts in the key being a section of the wards. To make a really complicated box of wards, and to cut keys which shall accurately fit their sweep, is a matter requiring considerable manual dexterity; and some warded locks are therefore expensive. But even with the best of them, all that it is necessary to do for opening the lock is to take a blank key which will properly fit the keyhole, coat it with wax, and then inserting it in the lock, press it round against the wards, which will cause them to leave an accurate impression of their section on the key. The parts impressed are then cut out with small files, drills, and saws, and the occasional use of fine cross-cut chisels. The key will then pass those wards which impressed themselves upon it; and if these are theonly wards, it will go completely round and open the lock. If there are also other wards in addition, not brought up flush with the first wards, the key is waxed again and pressed against them, and then further cut out, as before. This process is evidently one of absolute certainty, and the key so made is in all respects as capable of mastering the lock as the original key.
These warded locks are however easily opened with merely a piece of bent steel wire,—bent into such a sweep as will reach right round the wards instead of passing amongst them, thus escaping all chance of being obstructed by them. Such an instrument is called by burglars a “twirl.”
The fixed-guard or warded lock was the one in general use in the middle ages.
The next kind of lock is thetumblerlock, in which the bolt is moved backwards and forwards by the key as usual, but these movements cannot take place till a small lever with a stump on one side be lifted. This lever and stump form the tumbler, which is held down by a spring; and in the tail of the bolt are two notches, into one of which the stump fits when the bolt is shot, and into the other when it is withdrawn. All that is necessary to effect the picking of this lock is to lift the tumbler high enough for clearing the stump out of the notch, and then draw back the bolt. The tumbler may be lifted with one pick, and the bolt drawn back with another; but generally one pick will suffice for both purposes.
In the Barron tumbler lock the principle of double-action was introduced.
The next improvement was theleverlock properly so called, under which designation the majority of the modern locks may be classed.
The Bramah lock was an admirable contrivance with remarkably beautiful mechanism contained in a small compass; and since its invention there have been several ingenious modifications of the same principle in different radial locks,such as the Yale lock, in which the slides move radially instead of axially. One advantage in these radial locks is the greater difficulty in copying the keys, in comparison with the flat keys of ordinary lever locks: this difficulty however is not an insurmountable one.
A very ingenious addition was made to the action of the lever lock in Newell’s American lock, which was shown in the 1851 Exhibition, and described atpage 89of the present volume.
Though locks such as those already referred to exhibit great dissimilarity of construction, yet there is one point in which they all agree, and that is in the possession of a direct passage from the outside to the works. Although various locks have been devised with the object of having no direct passage to the works from the outside, one consideration shows the inevitable existence of such a passage; namely, that without it the key could not possibly at one and the same time touch the hand of the operator and the works of the lock. It therefore follows that any instrument which can pass in the same space as the key may be brought to bear on the works, whatever may be their construction.
It can now be shown that, if picking instruments are thus brought to bear on the works through the keyhole, there is a regular tentative system whereby the picking of any lock with an open keyhole can sooner or later be effected.
From the foregoing observations it is evident that there are two important defects in the principle of the previous lever locks, which being defects in principle are fatal to their security; namely, the means of access to the works of the lock through the keyhole, allowing of a series of attempts being made to open the lock by picking instruments; and also the facility afforded for repeating the trial of a false key made from a wax impression of the true key, and thus perfecting it by successive alterations after trial. In consequence of the possibility thus allowed of making these successive attempts either by picking instruments or by a falsekey, it has been shown by the cases that have occurred of locks of the best makes which have been falsely opened, that, however numerous and complicated may be the secondary impediments introduced into these locks, there can be no real security against the ultimate success of sufficiently numerous and persevering attempts, except by the adoption of some new principle of construction specially meeting the above two defects.
Adytic lockfig. 53.
fig. 53.
In the invention of the Improved Lock and Key now to be described, and which has been termed theadyticlock,[13]the writer’s object has been to meet this requirement. Infig. 53is shown an elevation of this lock, such as is made for an iron safe; two of the front cover plates being removed to show the construction.
[13]From the Greek αδυτος,inaccessible.
[13]From the Greek αδυτος,inaccessible.
The headBof the main bolt is of such a thickness as to be flush with the face of the leversLand guardA; and thestrap or tailDof the bolt is thin, and passes behind the levers and guard, and also behind the plateH H. The part of the tailDwhich would lie under the leversLand cylinderCis removed, as seen infig. 54, and replaced by a separate flat plate or stump-bolt, carrying the stumpS. This stump-bolt has a projectionKupon it, let into a recess in the tailDof the main bolt, but with1⁄10th inch vertical play in the recess. A spring in the tail of the main bolt presses the stump-bolt downwards, keeping the stumpSin the notches of the leversL, as shown infig. 53. The stump-bolt can thus descend1⁄10th inch at first without moving the main bolt, and this amount of vertical movement is sufficient to carry the stump in and out of the notches in the levers; but the stump-bolt cannot descend further without taking the main bolt with it.
Adytic lockfig. 54.
fig. 54.
Adytic keyfig. 55.
Adytic keyfig. 55.
fig. 55.
Immediately in front of the bolts comes the fixed plateH H, in which is cut the cam groove shown by the dotted lineJ J; and also the vertical slotEfor the pinPto work through, together with another vertical slot in which the stumpSfits and works. This plate carries the centre pinUon which the leversLturn. The levers are six in number, though anyother number may be used; and they occupy collectively3⁄8ths inch thickness. In front of the plateHis fixed the guardA, which is made of iron or steel, and has the brass cylinderCground into it. The guard is made a shade thicker than the leversL, in order to prevent the back plateHand the corresponding front plate from being so tightened on the levers as to impede their freedom of movement. The cylinderCis the same thickness as the levers, excepting the centre bossF, which projects from the back of the cylinder and works in a bearing in the back plateH, and also projects in front through the thickness of the two front cover plates. The small keyhole in the centre of the boss goes only a short distance into the cylinderC, being merely for the purpose of enabling the stem of the keyM,fig. 55, to turn the cylinder; the bit of the key is a separate piece,N,fig. 57, which is inserted through a separate keyhole into the radial slot of the revolving cylinderC, as shown atNinfig. 53.
This radial slot is cut in the side of the cylinderCthat is furthest from the levers when the cylinder is in the position shown infig. 53; and in the slot fits the slide blockR, which is a steel block having a pin projecting on each side. The back pin enters the guide grooveJ Jin the back plateH, as shown by the dotted line, and the front pin enters the corresponding guide groove in the front cover plate, which is shown removed. The back pin of the slide block projects through the back plateH, as shown infig. 56, and works in the cam grooveOin the tail of the stump-boltS,fig. 54, which is so shaped that as the slide block travels round the guide grooveJ J, shown by the dotted lines, it moves the stump-boltvertically as may be required according to the position of the bolts and levers.
In the position of the lock shown infig. 53, the bitNhas been inserted into the vacant space of the radial slot in the cylinderC, in front of the slide blockR. The size of this vacant space is3⁄8ths inch long by1⁄8th inch wide and3⁄8ths inch deep; and in the two front cover plates of the lock, and also in the door to which the lock is attached, a hole is made of the same shape. In the door there is no bearing for the centre bossF, but only a small keyhole corresponding in size with that in the bossFfor inserting the stem of the key.
Adytic lockfig. 56.
fig. 56.
In the position of the parts shown infig. 53, it will be seen that the leversLare held pressing down against the circumference of the cylinderCby their springsIbearing against the pinP. In this position also the bolt spring between the main bolt and the stump-bolt,fig. 54, presses the stumpSdown into the notches of the levers, so that the levers are completely locked by the stump, as seen infig. 53.
In order to unlock the lock, which infig. 53is shown with the bolt shot, it is necessary that all the gatingsGin the levers should be brought precisely under the stumpS. Through the centre keyholeFthere is no communication possible at any time with the leversL; nor will any instrument, however slender, if passed into the radial slot through the aperture atNbe able to reach them, whether the cylinderCbe in the position shown infig. 53or turned round into anyother position. For the only difference made by turning the solid cylinderCis that the radial slot in it is carried away from the aperture in the external plates, and the solid part of the cylinder is brought opposite to the aperture, which is thereby completely closed against the insertion of a picking instrument. This construction accordingly not only precludes the possibility of opening this lock with an ordinary key, in which the part that acts on the levers is attached to the stem of the key, but it also renders it an absolute impossibility to introduce a pick of any form, as nothing can reach the leversLexcept a detached piece of such a size and shape as to be capable of travelling round in the vacant space left in front of the slide blockRin the radial slot of the cylinderC.
Lock bitfig. 57.
Lock bitfig. 57.
fig. 57.
For the purpose of unlocking the lock the bitN,fig. 57, is used. This bit is of such a size as to fit into the vacant space of3⁄8×3⁄8×1⁄8inch in the radial slot of the cylinderC; and the indent atVis merely for the purpose of ensuring the insertion of the bit in the right direction, the external aperture for the bit being made with a corresponding projection to fit the indent in the bit. This bit being inserted through the aperture in the door, is pushed in by means of the key stemM, which is flattened on two sides for that purpose, as shown infig. 55; and the bit is thus pushed home into its place in the radial slot of the cylinder, as shown atN,fig. 53.
The key stemMis now inserted into the centre keyholeF, and the cylinder is turned round by it in the direction shown by the arrow, carrying round the slide blockRand the bitN. The slide blockR, while moving through the concentric portion at the commencement of the guide groovesJ J, does not affect the bit; but by means of the cam grooveOin the tail of the stump-bolt,fig. 54, it moves that bolt so far as to lift the stumpScompletely out of the notches in the leversL, which are thereby left free to be raised. On continuing to turn the cylinderC, the eccentric part of the guide groovesJ Jcausesthe slide blockRto move outwards along the radial slot, pushing the bitNbefore it; and the bit is thus made to project beyond the circumference of the cylinder, which it can then do, being no longer confined by the guardA. The further projection of the bit as the cylinder revolves causes the steps in the bit to lift their respective levers; and the steps in the bit are so arranged that, when the cylinder arrives at the position shown infig. 58, all the gatingsGare brought simultaneously opposite the stumpS, which is instantly shot down through the distance of the1⁄10th inch play by the bolt spring. The bitNremains in contact with the extreme partTof the levers while the stumpSis entering the gatings, the action of the bolt spring being so rapid that the bit cannot move through any appreciable distance during the time.
Adytic lockfig. 58.
fig. 58.
In other locks a spring action of this kind would greatly facilitate the picking, inasmuch as it would afford the gentle uniform pressure desired upon the levers. In other locks, therefore, the bolt is caused to move, and the stump toenter the gatings, by the direct contact of the key with the bolt, instead of by a spring; but as the key, while moving the stump into the gatings, is also altering its position under the levers, a slight tremulous motion of the levers is thereby occasioned, which no care in manufacture can obviate. This tremulous motion is aggravated by the circumstance that, as the keyhole is open to inspection, it is necessary to make all the levers fit flush with one another when down, in order to avoid affording any clue to the shape of the key from the positions of the levers; but as the various steps of the key, being of different lengths, describe different arcs, the curves of the levers when raised are of necessity in error to them all. The result of these combined faults is that the gatings have to be made wider than the stump, to allow a sufficient amount of play, thus introducing a fatal element of insecurity in the construction of the lock, since the security is of course enhanced in proportion as the gatings fit the stump accurately. In the new lock, on the contrary, the arcT,fig. 58, in each lever, can be shaped truly to its own proper radius, independent of all the rest of the levers; and as the action of the stump is instantaneous in catching the gatings as soon as they are all brought simultaneously under it, the stump and gatings can be made to fit one another with the most perfect accuracy, and without the slightest play.
On turning the cylinderCfurther round, the bitNpasses from under the levers, which remain held back by the insertion of the stump in the gatings; and just before reaching the position shown infig. 59, the slide blockRhas pushed the bit completely out of the radial slot, and the bit falls down as shown infig. 59, and drops through a hole into the inside of the safe that is locked. At this point the back pin of the slide block comes in contact with the lower side of the cam grooveOin the stump-bolt,fig. 54; and by turning the cylinderConwards to the position shown infig. 60, the withdrawal of the boltBis completed, bringing the parts into the position shown infig. 60. In these drawings only one leverLis shown; but there are altogether six levers, as shown in the sectional plan,fig. 56. The pinPis fixed in the tailDof the main bolt, so as to travel with the bolt; and by this means the springsIare released from strain, as shown infig. 60, as soon as the bolt is withdrawn.
Adytic lockfig. 59.
fig. 59.
From the nicety with which the various parts of this lock are constructed, it is evident that the levers must be very accurately lifted by the bit of the key in order to withdraw the bolt; and therefore any error in the bit, such as would occur with a false bit, will effectually prevent the lock from being opened. This may be illustrated by supposing the false bit to be so close an imitation as to have five of its steps absolutely correct, and the sixth only slightly wrong: though it is almost impossible that such a near approach to correctness could be attained in practice. The counterfeit bit being inserted in the lock, and the cylinder turned round, all will go on the same as with the true bit, up to the time when thefalse bit reaches the pointTof the levers, as previously shown with the true bit infig. 58. Here a change of action takes place; but what is the nature of the change the operator has no means as yet of ascertaining. In the case supposed, where five of the steps in the bit are right, but the sixth is wrong, the gating of the sixth lever does not precisely coincide with the others, nor with the stumpS; and the consequence is that, at the critical moment when the stump ought to spring into the gatings and hold back the levers from falling forwards, it will be prevented from entering the gatings, owing to the entrance being partly blocked up by the one lever, which stands more or less across it.
Adytic lockfig. 60.
fig. 60.
The fact, however, that the stump cannot enter the gatings, does not become known to the operator until the cylinderChas been turned further round, so as to bring the slide-block pin in contact with the lower side of the cam grooveOin the stump-bolt; and before this point has been reached the false bit has already passed clear of the levers, which, not being retained by the stump, are instantly thrown forwards again by their springs, and locked in their original position by thestump entering the notches. At the same time the false bit has dropped into the inside of the safe in the same manner as the true bit, as shown infig. 61.
Adytic lockfig. 61.
fig. 61.
Hence a person putting a false bit into one of these locks will not only infallibly lose it at the very first trial, but will do so without gaining any information as to the nature of its inaccuracy; for as the gatings of the levers cannot be seen or felt, all that can be told about the action of a false bit is, that it has failed to open the lock. In fact, a counterfeit bit passes under the levers, and through the lock, just like the true bit; and it is only the stoppage afterwards met with of the bolt that indicates the failure of the false bit, which is by that time gone beyond recovery. Whatever amount of labour, therefore, may have been spent on the fabrication of a counterfeit bit, this bit can only be tried once, so that no alteration can afterwards be made in it.
Nothing that can be inserted into the radial slot of the cylinderCthrough the aperture in the front plates can do any injury to the lock; and a charge of gunpowder inserted inthat way would only blow out again at the orifice without damaging the lock, both the apertures for the key being merely blind holes with parallel sides.
Key cutterfig. 62.
fig. 62.
Key cutterfig. 63.
Key cutterfig. 63.
fig. 63.
For the manufacture of the bits for the keys of this lock a self-acting machine is employed, in which the height and width of the several steps in the bit are regulated by adjustments of very great accuracy, and admitting of an almost endless variety of figure for the bits. This key-cutting machine is shown infigs. 62to64, and consists of a small circular sawArunning vertically, of the samethickness as each step in the bitI, which is brought up to the saw by the slide-restB. The bitIis fixed in the holderC, which rocks upon a centre, so as to give the required curvature to the edge of each step in the bit when cut bythe saw, as shown in the full-size section of the bit-holder,fig. 63. The adjustment of the depth of cut is effected by the set screwDupon the slide-rest coming up against the eccentric ringEupon the bed of the slide-rest; this ring is turned round by hand, and set to sixteen different positions by means of the catch-pinFand the sixteen holes on the circumference of the ring, allowing of sixteen different depths of cut. The lateral adjustment for the pitch between the successive steps of the bit is effected by the two bed-screwsG Gacting on the slide-restB, having a dividing plate on the head, and such a pitch of thread that one turn of the screws traverses the slide-rest through the exact distance of one step in the bit. The occurrence of any play or backlash is entirely prevented by having the screws placed one at each end of the slide-rest; so that by slacking back one screw through one or more turns, and then advancing the other through the same number of turns, the slide-rest is always held with perfect steadiness between them, filling exactly the space between the ends of the two screws.
The number of changes admissible in this key-cutting machine, if used for making keys for locks having six levers, is the number of permutations that sixteen terms are capable of when taken six together, which is upwards of sixteen millions. Some of these changes are so slight that too great accuracy of workmanship would be required to make the locks accordingly; but of those changes that differ from one another so far that no lock could be opened by any other than its own key, more remain than could be used up by all the locks in the world.
Key cutterfig. 64.
fig. 64.
The writer may observe that it was the study of the circumstances of the great gold robbery on the 15th of May, 1855, by Agar and his confederates (when two of the best lever locks were picked, and gold stolen weighing upwards of 200 lbs., while in transit on the South-Eastern Railway from London to Paris, packed in three sealed iron-bound boxes, inclosed in a bullion safe, secured by those locks),and of the various modes of picking locks, which led him to turn his attention to the achievement of what had been so long and perseveringly sought after, namely, an unpickable lock. The principle of a detached bit has been previously tried, in so far as that locks have been made in which the bit of the key was deposited in the lock by unscrewing the key stem, and then withdrawn by screwing in the stem again. But inasmuch as the detached bit, even though it failed to open the lock in the case of a counterfeit key, could always be brought back again to the keyhole and removed, this admitted of a repetition of attempts with successive alterations of the one counterfeit key, without the certainty that any warning would be given by the lock of such attempts having been made.
In another still more complicated lock with a detached bit there were two keyholes, into one of which the bit of the key was put, and the stem being then unscrewed from the bit, was put into the second keyhole and turned round so as to close the first keyhole over the bit; a separate handle was then turned to work the lock, six separate operations being required for either opening or closing the lock. Further, a kind of retainer has been attempted by so arranging the lock that, if any key was put in but the right one, it was held in the keyhole in such a manner that it could never be got out. In this case, however, if the false key would not open the lock, neither would it let even the right one do so, and it would be necessary to break open the door secured by the lock.
In the new lock here described, the special points that have been aimed at are the following:—
Firstly, in no position of the lock is there any access to the works from the outside through the keyhole. This access through the keyhole is more or less a defect in all other principles of lock, as it admits of feeling and manipulating the works for the purpose of getting information for picking thelock in the absence of the right key; whereas in the new lock there is no opening whatever at any time, except the two plain parallel recesses into which the key and the bit are fitted. From the moment the turning of the lock commences both these recesses are effectually blocked up: the one for the bit being conveyed bodily away from the keyhole, and its place taken by the solid metal of the cylinder; while the other is completely filled by the key, which cannot be withdrawn except by turning it back to the original position. In consequence of this construction no injury can be done to the lock by explosion of gunpowder in the keyhole, the only openings from the outside being parallel at their sides, and not communicating with any portion of the interior of the lock; and the simplicity and solidity of construction are such that the revolving cylinder is made practically air-tight within its bearing. This effectually prevents all attempts to open the lock by picklocks, and leaves no alternative but the attempt to make a sufficiently accurate copy of the true key.
Secondly, as no clue whatever can be obtained from the outside of the lock respecting the key required, the attempts upon the lock are thus limited to the chance of obtaining a wax impression of the true key. The difficulty of making a counterfeit key sufficiently correct by this means for opening one of the best of the previous constructions of lock is very great; but in the new lock this difficulty is greatly increased by the fact of the levers remaining absolutely stationary while the stump enters the gatings, in consequence of which the gatings are made so close a fit to the stump that an exceedingly minute error in the lifting of any of the levers is sufficient to prevent the lock being opened. This extreme delicacy of construction can be carried out practically without objection in the new lock, because there is no possibility of putting a strain from the key upon the stump, so as to cause injury by forcing it at the moment of entering the gatings; for the only force acting upon the stump at that time is the uniform pressure of its own spring. In addition to thissource of increased safety, there is the still more important circumstance that only a single trial can be made of each counterfeit bit; because, if carried forwards far enough to try its effect in opening the lock by passing the levers, the bit is inevitably lost by falling through the lock and inside the door. Thus not only is all chance prevented of a second trial with the same key, but the bit retained inside the door gives warning of the attempt having been made, and shows how near the counterfeit key has approached to the original. The numerous cases that have occurred of attempts to open locks by counterfeit keys, such as the remarkable instance previously referred to, show that even with the most practised hands it is next to impossible to make from a wax impression a key that will serve for opening a good lock the very first time it is tried; and the striking importance is therefore seen of this arrangement in the new lock, which prevents more than a single attempt being made with a counterfeit.
Thirdly, another advantage to be named in this lock is that the stem alone of the key is required to lock it, but it can only be unlocked by the complete key. The stem, therefore, can be left by the principal of an establishment for locking up by a subordinate; but the bit, which is the essential part of the key required for opening the lock, need never be used or seen by any one but the principal himself. As the hole in the external door-plate for the stem of the key has a notch on one side only to admit the key stem, and the cylinder is prevented from making a complete revolution, the stem of the key cannot be withdrawn from the lock except when the bolt is shot; so that its absence from the keyhole serves as a proof that the bolt is shot.
Fourthly, one other advantage in this lock is its simplicity and solidity of construction. It contains no more parts than the simpler forms of lever lock having the same number of levers, and the total number of separate pieces in the complete lock is only sixteen. The principle of security, therefore, upon which the new lock is constructed, avoids entirely thecomplications and the delicate and minute class of work rendered necessary in other locks by the use of detectors and the other auxiliary contrivances employed for increasing the difficulty of picking.
Mr. Fenby exhibited, at aconversazioneof the Institute of Civil Engineers, and at the meeting of Mechanical Engineers, specimens of his adytic lock, and showed its action both with the true key and with counterfeit keys; and he showed by trial that the counterfeit failed to open the lock, notwithstanding that by means of the permutating cutting machine it had been made a much nearer approach to a perfect copy than was practicable in the best handwork from a wax impression. He also exhibited the key-cutting machine employed for cutting the bits; and also a set of burglar’s tools employed for drilling into the door of an iron safe sufficiently for breaking open or removing the lock, showing that the hold required for giving the cutting pressure upon the powerful drill employed for the purpose was obtained by a steel cross piece inserted into the keyhole and turned at right angles, so as to hold across inside the lock; but in the new lock, as the keyhole had no opening into the lock, and only a slight shoulder on one side, no means were afforded for obtaining the required hold for the drill.
The following are the salient points of the discussion that followed the reading of his paper:—
The Chairman remarked that the paper just read gave a very excellent and clear description of the detailed working of the new lock, and he thought this construction of lock was a most valuable one, as affording real security against all fraudulent attempts. He inquired whether there would be any possibility of tampering with the lock by examining it upon the inside of a safe door, whenever the door might happen to be left unlocked.
Mr. Fenby replied that there was no means of tamperingwith the lock from the inside of the door, as the two keyholes for working the lock were only in the front face of the door, and the lock was all closed up on the inside of the door, excepting the hole through which the bit was allowed to drop out; but this would be useless for the purpose of tampering with the lock, as the bit dropped down a tube leading to the bottom of the door, through which no examination of the lock could be successfully made.
The Chairman inquired whether there was any provision against the bit being accidentally locked up inside the safe, in which case it appeared the lock could not be opened again.
Mr. Fenby replied that the owner of the safe must of course be careful after unlocking the safe to take the bit out before locking it again, otherwise there would be no means of opening the lock afterwards with that key. As a precaution, however, against any such accident, each lock was provided with three bits, all duplicates, one of which would be kept in the pocket for use, while the two others would be preserved in a place of safety for the chance of any such contingency. Moreover, in most of the safes fitted with these locks, the tube through which the bit dropped had been made of such a length as to carry out the bit on opening the door, dropping it into a small tin tray outside the safe; and by this means the accidental locking in of the right bit was rendered impossible. One of the advantages of the new lock was that the stem of the key was not required to be kept constantly in the possession of the owner, but it might be left in the lock, as the bit alone was the valuable part of the key; and as the bits were of such small size and convenient shape, a number of them might readily be kept in the pocket by a person having charge of a number of safes, without the inconvenience attending a large bunch of ordinary keys. In the case of an attempt being made to open the lock with a counterfeit bit, the advantages of retaining the counterfeit inside the safe were not merely that the person attempting the lock was deprived of his instrument, while the proprietor immediatelydiscovered the attempt upon the next occasion of opening the safe; but the retention of the counterfeit itself afforded the means of judging, by a comparison with the true bit, whether the attempt had been made altogether in the dark as to the actual construction of the lock, or whether it was likely that some clue regarding the true bit had been obtained by means of a wax impression or otherwise. In the latter case the owner of the safe might think it desirable to have the lock taken off, and the arrangement of the levers altered, and a new bit made so as to baffle any further attempts.
Mr. W. S. Longridge observed that the inconvenience that had been alluded to with the new lock, of accidentally locking up the bit inside the safe, was no greater than occurred with an ordinary safe lock if ever the key was accidentally lost; in either case, unless the precaution was taken of keeping a duplicate in reserve, it would of course be necessary to have the safe broken open.
The Chairman inquired how the ideas had been arrived at of separating the bit from the key, and of preventing all access to the works through the keyhole, and also of retaining the bit inside the door after any attempt at unlocking.
Mr. Fenby replied that his attention had in the first instance been attracted to the subject of the picking of locks as a mechanical problem, and he had found that there had hitherto been no principle in lockmaking which could effectually baffle persevering attempts at picking. For although there were certain complicated constructions of locks, having many points of excellence, they had all yielded in time to the picking instrument in clever hands; and it must be remembered that any individual lock when once constructed remained stationary as regarded subsequent improvement, whereas the art of picking that lock was continually progressing towards success, with all previous constructions of locks, and it was clear therefore that the lock must ultimately be defeated. He had been further stimulated in the investigation of this subject by the occurrence of the great gold robbery referredto at page 188; and the circumstance which had struck him most forcibly in connection with that robbery had been that locks of the best make hitherto known had admitted of seven successive trials being made upon them without detection, each trial furnishing the information for further perfecting the counterfeit key, until the locks were at length opened.
These considerations had led him to the conclusion that two points were established and were required to be kept in view for the construction of any lock that should be really secure against fraudulent attempts. The first point was that wherever a man could get instruments into the lock he could ultimately solve any problem laid before him by the maker of the lock, as the lock when once made could be tried any number of times if an instrument could be got into it at all. Hence he had concluded that it was requisite for all access to the interior to be cut off, so as to preclude all possibility of getting a pick-lock in; and this was accordingly accomplished by adopting the plan of separating the bit from the stem of the key. The second point established was that it was necessary to prevent the possibility of making a succession of trials with the same counterfeit key; and it had then struck him that, if the bit of the key were arranged to drop inside the safe in unlocking, there would be no means of going on gradually improving and touching up the counterfeit from the results of previous trials, as the false bit would be irrecoverably lost in the very first attempt, without furnishing any clue whatever as a guide for alteration in a subsequent trial. The first lock that he had invented for meeting the requirements thus pointed out had been made with a solid block having a tunnel through it, but involving the same principle of retaining the bit of the key and keeping the levers inaccessible from the outside. Subsequently, however, he had abandoned that construction and produced the new lock shown in the drawings, having the revolving barrel with radial slot.
The Chairman proposed a vote of thanks to Mr. Fenby for his paper, which was passed.
This lock has been designed with a view to doing away with several weak points in the construction of lever locks.
The introduction of the movable stump by Mr. Hobbs, in order to defeat picking by the tentative method of applying pressure to the bolt, so as to cause binding between the stump and the levers, was a great advance in the art of lock-making.
The movable stump, as so constructed, was, however, open to this objection, that while sufficiently delicate and certain in its action to render picking very difficult, it was at the same time, through the smallness of its parts—resulting from the confined space available for its action—unsuited to withstand any amount of force applied to push back the bolt.