A Dissertation on the Construction of Locks (1815)
A
DISSERTATION
ON THE
CONSTRUCTION
OF
LOCKS.
A
DISSERTATION
ON THE
CONSTRUCTION
OF
LOCKS;
CONTAINING
BY JOSEPH BRAMAH, Engineer.
SECOND EDITION.
London:
Printed for the AUTHOR, No. 14, Piccadilly;
And Sold by J. Taylor, at the Architectural Library,
59, High Holborn.
1815.
ADVERTISEMENT.
In offering to the public a Second Edition of the “Dissertation on the Construction of Locks,” the Editor regrets, that in justice to the Invention described, and to satisfy those who employ it, he is reduced to the painful necessity of replying to some unfounded reports, which have been industriously and insidiously circulated to a very considerable extent.
It may be proper to observe, that the spirit and perseverance evinced by Mr. Bramah, in giving complete effect to his Invention by the introduction of a new system of Machinery, occasioned disbursements which the sale during the term of his Patent failed to replace, and he therefore solicited the Legislature for an extension of the term. But the difficulties and impediments opposed to the measure, when under consideration of a Committee of the House of Commons, so far delayed its progress, that it appeared more than probable the existing Patent would expire before the customary forms could be gone through; the Bill in consequence was withdrawn, and the only proceeding of the Committee was the examination of two gentlemen on the part of its opponents, who are reported to have, there, picked a Lock constructed on this principle, with a piece of wood and a quill.
The Editor therefore has thought it necessary to subjoin an Authentic Extract from the Minutes of the Proceedings of the said Committee, taken verbatim as delivered, and containing such part as comprised a complete summary of all the observations made; and which he trusts will entirely remove any unfavourable impression, if it is possible such can remain, after an attentive perusal of the following pages.
With respect to these Witnesses, whose principal aim was to establish a position that the key is more easily copied than any other, it is not questioned they gave, or thought they gave, an honest opinion; yet, when men are in determined hostility to a purpose which promises to affect their interest, their judgment may reasonably be suspected to want the freedom of perfect disinterestedness; especially when given without Oath. Admitting however to the full extent, what long and uniform experience most decidedly contradicts, that the key is easily copied, it cannot fairly be urged as defeating the merit of the Invention. All keys may be copied, alike in wood, or any other material, which has hardness enough to overcome the friction of the Locks; the one in question will clearly appear to an unprejudiced observer, to require that mathematical similitude which the greatest care alone can produce. But if this ideal excellence was attainable, if the key could receive a form to which neither the vicious nor the ingenious could supply a counterpart, its use must be very limited; for the purchaser of a Lock, placing property under its protection, most undoubtedly guards the key with the same solicitude that he would the property which it secures.
When the Witness therefore admitted, that without the key he could not open the Lock, the Inventor considered him to grant all that was necessary to prove the extreme utility and perfection of the Invention—an opinion in which he trusts his readers will readily coincide.
EXTRACT
Mr. George Hawkes (concerned in extensive Iron Manufacture, in the Counties of Durham and Northumberland), examined.
“The first Lock that I ever had in my hands of Mr. Bramah’s, was yesterday seven-night—it was a Till Lock: on looking at the key I thought it very easily copied by a piece of wood of any substance, that a pen-knife would cut. I considered, if I was right in my idea, that the principle of the Lock must be a dangerous one, it being very usual with the Masters of retail shops to leave their key, at some period or other, with the servant.”
- Cross-examined.
“When you made that key of wood, had he not the real key in his possession from which he copied it?”
“YES.”
“I DON’T MEAN TO SAY SO.”
Mr. Henry Downer (Ironmonger), examined to the same effect as first Witness (Hawkes), and the questions put to same effect.
- Cross-examined.
“Had you not the real key in possession when you made what you call the mutilated key? And did not you copy it?”
“I HAD, AND I DID COPY IT.”
A true Extract.
| (Signed) |
Hen. Coles, Committee Clerk. |
May 24, 1815.
DISSERTATION,
&c.
The protection and preservation of life and property, are objects which have been anxiously and necessarily attended to in the most harmless states of society; and the invention of ingenious men, has in all times been applied to contrive means of security adapted to resist the nefarious practices of the day. A review of their productions, which we must presume to have been effectual to their purpose, suggests a conclusion, that the morals of former times, were as much less depraved than those of the present, as the mechanical contrivances for security were less excellent; and the progress of a disposition to rob and defraud, may perhaps be more accurately traced in the works of art that were formerly used for security and defence, than on any other principle or ground of reasoning. It is certain, however, that no invention for the security of property has yet been offered to the world, which the ingenuity of wickedness did not find means to defeat; nor is it probable that the genius of any one man will ever strike out a method, by which all the arts and manœuvres, practised in the science of robbing, may be effectually counteracted. Modern depredation is reduced to a system, in which art and force are exerted with such skill and power, as to elude precaution, and to defy resistance. The dread and anxiety, which every inhabitant of the metropolis and its environs, must feel in the reflection that he sleeps with no other assurance of safety, but the hope that chance, among the multitude of objects, may direct the invaders of the night to some other victim, is an evil which cannot be contemplated without horror. Yet it is not in humanity to behold the numberless sacrifices made to justice, without lamenting the ineffectual severity of the law; and earnestly wishing to reduce the number of executions, by opposing methods of prevention, to the enormities which lead to such a dreadful end. It is a maxim in morals, that no man becomes at once completely wicked. The timidity which attends the first act of dishonesty, and the remorse it excites in the unpractised offender, are a natural, and in general a sufficient check to the commission of very enormous crimes, till the mind is tainted by evil councils, or becomes hardened by the frequent repetition of petit offences. To remove all temptation to dishonesty, and to give as few opportunities as possible to the indulgence of evil propensities, is as much the duty of those who possess, and wish to preserve their property, as obedience to the law, which forbids to steal, is the duty of those who may be tempted to deprive them of it. For the servant, who would never have meditated an attempt upon the chest which contains his master’s treasure, may be tempted to purloin his purse if carelessly thrown in his way. To secrete objects of temptation, and prevent access to them by every possible security, seems therefore to promise more towards lessening the number of robberies, than the dread of any punishment, which the law of England can inflict.
A desire to reduce this theory to practice, induced me to apply my utmost thought and attention, to contrive an effectual impediment to the most frequent, and not the least fatal methods of robbery. 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 recompence the difficulty and hazard of the enterprize; and till some method of security be generally 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 dependance on the security of common Locks, even of those which are constructed upon the best principle of any in general use, is fallacious. To demonstrate this bold and alarming proposition, I shall first state the common principles which are applied in the art of Lock-making; and, by describing their operation in instruments differently constructed, and possessing different degrees of excellence, prove that the best constructed Locks, with fixed wards, are liable to be secretly opened with great facility; and 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. I shall then proceed to the specification of a principle, which by great application and expence, has been completed, and is now offered to the notice of the public, as a perfect security against every possible effort of art and ingenuity; and which I submit to the most critical investigation of curious, and skilful judges, with a confidence which assures me, that their testimony will do credit to the inventor, by confirming the efficacy, the infallibility, and the originality of the contrivance.
The principle on which all common Locks depend, is that of applying a lever to an interior bolt by means of a communication from without, which moves it in such direction as the lid, drawer, or door to be secured may require. The security of such Locks therefore, and their comparative excellence, are determinable by the number, variety, and disposition of the wards, or other impediments inserted in the passage, by which the lever or key is conveyed to the bolt; if these out-works do not secure the bolt from the intrusion and application of every instrument but its proper key, the Lock is inadequate to its intended purpose; and however intricate or difficult the passage to the bolt may be rendered by a skilful and judicious disposition of the wards; yet, if any access to the bolt is practicable by a workman of equal skill with its maker, the Lock is defective in the main point of excellence, which is effectual security, and is entitled to no higher claim than comparative merit.
The construction of Locks, is a subject on which many ingenious mechanics have employed their thoughts; and the art has received many and great improvements from their labours. 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 to the 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 if they 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 variations 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 key-hole, and the shank of the key bored to a sufficient depth to receive the pin, nothing remains but to colour 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 to pass 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 hath effected a free passage to the bolt. And in this operation he is directed by an infallible guide: for the pin being a fixed centre on which the key revolves without any variation, and the wards being fixed likewise, their position must be accurately described 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 detract from the merit of such inventions, nor to dispute their utility and importance. Every approach towards perfection in the art of Lock-making may be productive of much good, and is at least deserving of commendation and encouragement; for if no higher benefit were to result from it, but the rendering that difficult or impossible to many, 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.
The first claimant to merit in this branch of mechanics is Mr. Baron, whose Lock is undoubtedly more secure, than any that ever was in use before his invention was made known. An observation or two upon Mr. Baron’s Lock, will however illustrate what I have said on the subject of fixed wards, and prepare my readers to comprehend more readily, the principle on which my own Lock is constructed.
It appears from the object of improvement which employed Mr. Baron’s attention in the construction of his Lock, that he was aware of the impossibility of guarding the avenues to the bolt so effectually by fixed Wards, as to prevent all access to it; for leaving the entrance and passage to the common protection of wards and outworks, his ingenuity hath been wholly applied to the interior fortifications of the bolt, by a judicious application of additional tumblers. These are a kind of grapple, by which the bolt is confined as well in its active as its passive station, and rendered immoveable, till set at liberty by the key. One of these instruments is commonly introduced into all Locks that are of any use or value; it is lodged behind the bolt, and is governed by a spring which acts upon the tumbler, as the tumbler acts upon the bolt. The application therefore of any force to the tumbler, which is superior to the force of the spring, will cause it to quit its hold, and set the bolt at liberty. And in this operation no skill or nicety is required, to ascertain the degree of force to be applied; for, it matters not how far the tumbler is lifted above the point, at which it ceases to controul the bolt. But Mr. Baron has improved upon the practised method of applying the tumbler, by confining their action within a circumscribed space, cut in the center of the bolt, of a dimension barely sufficient to the purpose they are intended to answer, and which space is provided with niches on the upper side, as well as the lower, into which the hooks are driven, if any greater force be applied to the tumblers, than is required to disengage them from the bolt. Hence it becomes absolutely necessary in the fabrication of a false key, that the pressure of the extreme point of its bit on the tumblers, be proportioned with the greatest exactness to the point of height to which they must be raised, to release the bolt; for otherwise, the power which disengages the hooks on the one side will fix them on the other, and still leave the bolt immoveable. This improvement, which does great credit to Mr. Baron’s mechanical invention, being as useful and important in effect, as it is new and curious in principle, must be admitted by every competent and impartial judge, to be a very valuable acquisition to the art of Lock-making. But greatly as the art is indebted to the ingenuity of Mr. Baron, he has not yet attained that point of excellence in the construction of his Lock, which is essential to perfect security.—His improvement has increased the difficulty, but not precluded the possibility of opening his Lock, by a key made and obtained as above described; for an impression of the tumblers may be taken by the same method, and the key be thence 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. Baron, as a remedy for this imperfection, because a less object would not have been worthy the exercise of his great ability; and, because (if such were his intentions) he did not over-rate the effect, which the cause was capable of producing. He seems evidently to have conceived the principle, but hath certainly failed in the execution. For, by giving an 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 his Lock is thereby rendered in a proportionable degree defective. To make these remarks more intelligible, I must entreat my readers to suppose the key with which the workman is making his way to the bolt, (by the process above described) to have passed the wards, and to be in contact with the most prominent of the tumblers. The impression which the slighest touch will leave on the key, directs 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, acquires as perfect a command of the Lock, as if it had been originally made for the purpose; and being thus brought to a bearing on all the tumblers at once, the benefit arising from the increase of their number, if multiplied to fifty, must inevitably be lost; for, having but one motion, they can act only with the effect of one instrument.—But nothing is more easy than to remove this objection, and to obtain perfect security from the application of Mr. Baron’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 could 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.[1]
The correction of this defect would rescue the principle of Mr. Baron’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 a 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. Baron’s ingenuity to make them durable.
Duration, and an exemption from many casual disorders, to which other Locks are liable, are qualities, which the projector of solid wards, appropriates in a peculiar degree to his invention. That they are more durable, and less subject to disorder, than wards more delicately constructed, are claims which I believe no locksmith will dispute with him. But, if his Locks are less exposed to the effects of time and chance, he hath certainly furnished them with keys, which do not possess the same properties. They are less formed for duration, and are more liable to accidental injuries, than the keys of any Locks I have ever seen. For the various angles they describe, unavoidably subject them to perpetual entanglements; and the stem, which in other keys is protected by the web, being left bare, is rendered considerably weaker, as well as more liable to be deformed; and of course must give more frequent occasion to call in the assistance of the locksmith. The key having thus lost as much, as the lock is said to have gained in point of duration, the degree of frailty is, upon the whole, undiminished; and, being less equally distributed, will of course be more inconvenient.
The resistance of picklocks, and the entire exclusion of false keys, is a property which is likewise ascribed to the solid-ward Lock. But to this excellence it hath no just pretention. For it possesses in common with all other Locks, the imperfection of being liable to be opened (in the manner above described) by a locksmith of any tolerable degree of skill; and it hath this peculiar disadvantage, that the key may be more easily copied, than those of the most common Locks.
I could add many reasons to those I have given, in proof of my original position, “that all dependance on the inviolable security of Locks (even of those which are constructed on the best principle of any in general use) is fallacious.”—But, presuming that I have proved by fair, and just observations, that Mr. Baron’s Lock is short of perfection, it would be a trespass on my readers to adduce further arguments to demonstrate that every other warded Lock is greatly deficient in the essential properties, and very unequal to the important purpose of an effectual security.
To find out and disclose irremediable errors in any system of art or science, which engages the confidence, and is necessary to the security or satisfaction of mankind, is the office of an invidious and unbenevolent mind. If, therefore, the defects and imperfections, which I have pointed out in the principle, or the construction of all other Locks, are not effectually remedied in that which I have so long offered to the public, as a complete, and as far as the Lock is concerned, an inviolable security; the communication of my observations will be more prejudicial than useful, and consequently more derserving of censure than commendation. But, if it shall appear that I have not wantonly divulged their defects, without offering at the same time a certain and effectual remedy, I may fairly hope my invention will receive that approbation and encouragement, which is due to great improvements, in objects of universal use and importance.
From the various methods which have been successively used to secure property, or to insure personal safety, it may be collected that the arts of violation have improved at least in an equal degree with the contrivances which mechanical ingenuity hath invented and applied for security. And this evil has arisen (in the case of Locks) from the misapplied efforts of ingenious mechanics, to effect that by a complex principle, which a simple one only can produce. In proof of one part of this proposition, I may refer to the most perfect Locks, that ever were constructed with fixed wards; to demonstrate the other, I shall give a specification of my own.
The idea of constructing a Lock that might resist every application and effort of art, was first suggested to me (as I have before observed) by the alarming increase of House Robberies; which, there is great reason to believe, are as often perpetrated by perfidious servants, or accomplished by their connivance, as by any means that are used by the common house-breaker. In this view of the evil to be remedied, it was evident, that a Lock or fastening, which might effectually exclude the one, would be no security against the other; and that no Lock would completely answer its intended purpose, unless a free and deliberate access to the key-hole could be rendered as useless to the purpose of obtaining a key by impression, as the picklock, and other instruments of mischief, may be rendered (to the purpose of opening the Lock) by the multiplicity and intricacy of its wards. The hasty execution of a midnight robbery, in which the servants of the family do not act a part, will not allow sufficient time, if proper instruments were at hand, to overcome the difficulties, which ingenious locksmiths have opposed to foreign invaders: my chief attention, therefore, was applied to contrive a security against the advantage which a domestic enemy possesses, in the opportunity of executing his purposes at leisure. But practicable as this appeared, I did not venture to attempt it by any means hitherto found ineffectual, not presuming to imagine I could give perfection to an instrument, which men of much greater knowledge and experience had left defective. I was, therefore, as solicitous to avoid their excellencies, as to escape their imperfections, which, are so blended in the best common Locks, as to make it impossible to adopt the one, without falling into the other. A very little thought on the subject convinced me, that success would depend on the application of a principle, as dissimilar as possible, to that, by which other projectors had in vain sought to attain perfection in the art of Lock-making. And as nothing can be more opposite in principle to fixed wards, than a Lock which derives its properties from the motion of all its parts, I determined, that the construction of such a Lock, should be the subject of my experiment.—In the prosecution of this purpose, various models were constructed; and I had the satisfaction to receive from the least perfect of them, the clearest demonstration of the truth and certainty of my principle, which has now been confirmed by a long and extensive trial. The exclusion of wards, made it necessary to cut off all communication between the key and the bolt; as the same passage, which in a Lock simply constructed, would admit the key, might give admission likewise to other instruments. The office, which in other Locks is performed by the extreme point of the key, is consequently here assigned to an internal contrivance, which cannot operate upon the bolt till every part of the Lock has undergone a change of position. The necessity of this change to the purposes of the Lock, and the utter impossibility to effect it, otherwise than with the proper key, are the points to be ascertained, by a specification of the component parts of the movement, and an explanation of their respective offices.
I shall now, therefore, endeavour to illustrate in a familiar manner, the general principle of my invention, and then shew that method of applying it in the construction of Locks, which has appeared in practice, the simplest and most effectual for the purpose.
Fig. 1. G represents a sliding bar or bolt, prepared to move in the frame K, which frame has six notches cut on two of its sides, parallel to each other, across the direction of the bolt, to admit the six sliders a, b, c, d, e, f, to move freely therein. For the same purpose also, the bolt has six corresponding notches, and the sliders being dropped therein, it is retained in its place or prevented moving, until the obstruction thus formed by the sliders is removed. 1, 2, 3, 4, 5, 6, shew the six openings on the sliders made indiscriminately at different distances from the bolt, precisely fitted to its width, and which must be brought exactly in a line opposite thereto, before it can be moved. The ends of the sliders at o, o, are the only parts intended to be exposed, and are all projected at equal distances from the frame K. In order therefore to give motion to the bolt, a complete tally or key H must be provided, with six unequal prominent surfaces, agreeing respectively with the distances of each notch from the bolt, and by the application of which the sliders may receive the motion necessary to bring the notches in a line and form a groove for the passage of the bolt. It will be evident, that in the absence of such a key or tally, no certain information can be gained by an inspection of the projected parts of the sliders; and, as they may be severally pressed farther than requisite, as well as not far enough, every attempt towards their due adjustment must entirely depend on chance, which by demonstration is found to offer such improbability of success as amounts to a most satisfactory security, and must deter any person, acquainted with the principle, from making a trial.
I shall now proceed to describe the application of this principle, in which it will be seen, that a method is provided of restoring the sliders to an even surface after the key is withdrawn.
Fig. 2, represents the face of a circular block or barrel of brass, having a cylindrical cavity throughout, and divided from the center into eight compartments, separated by grooves passing also quite through, and fitted with as many steel sliders. The upper parts of these sliders project into the cylindrical cavity and are elevated, to be flush with the prominence in the center of the barrel. The notch in one part of this prominence receives the bit or lever on the key which turns round the barrel in the operation of opening the Lock.
Fig. 3, is a section of a complete Lock; i, i, is the brass barrel, as Fig. 2, having a groove cut in the middle of its spherical surface of a depth equal to the notches expressed at different distances on the outer edge of the sliders l, l, and into which is fitted a thin plate of iron, shewn at Fig. 4, and divided in half for that purpose. This plate is screwed to the cap or covering, m, at n, n, with its internal edge to fit the cylindrical cavity; being previously notched thereon to correspond with the projection of the sliders in the groove: p, is a pin attached to a brass plate at the interior end of the barrel; the plate is made to confine the parts in their places on that side, and the pin carries a small socket, t, on which the overhanging ends of the sliders rest, and which by the action of the spiral spring keeps the sliders buoyant. The cap or covering plate, m, screws down to the external plate of the Lock, q, limiting the upward pressure of the sliders, and protecting all the operative parts. When the barrel, i, i, is moved round, the bolt, r, is thrown forward by a process which will be hereafter explained.
To give this machine, the property of inviolable curity, it was necessary to subject its motion to some restraint which the key only could remove, a power that is lodged in the thin plate, Fig. 4. This plate, as applied at n, n, Fig. 3, serves either to check or guide the motion of the machine, and these opposite offices the following will explain: on the edge of the plate which grasps the barrel are cut eight notches, into which the sliders, l, l, project; whilst they are thus confined, the motion of the machine is totally suspended, and the bolt so fixed as to defy every effort of art to move it. The sliders are upheld in their respective grooves by the elastic power of the spring on which they rest, till a pressure superior to that power is applied, and are again restored to their station by the re-action of the spring when the weight which depressed it is removed. All these sliders, as before observed, have a notch on the outer edge, disposed as irregularly as possible, and all admit of pressure beyond the point which brings these notches parallel with the plate. The necessity of the proper key to the purpose of opening this Lock, and the certainty that it cannot be accomplished by other means, will be clearly seen from the process which puts it in motion. By a distinct and unequal pressure on the sliders, the notches must be formed into a groove, in a line with the plate, n, n, which those notches are exactly fitted to receive. The least motion of the barrel while the sliders are in this position, will introduce the edge of the plate into the groove thus formed by the notches, and controling the power of the spring, permit the barrel to move round and protrude the bolt. The impossibility of thus bringing the notches on the sliders to fall into a direct line, and to form a groove which shall perfectly tally with the inner edge of the plate, n, n, by any other means than the application and impulse of the key, is the principle of security which constitutes the peculiar excellence of this Lock. The key is represented at Fig. 5, and its indented point or extremity corresponding with the depths of the notches is seen at Fig. 6. It will be recollected, that the upper ends of the sliders overhang, or project into the cylindrical cavity which forms the key-hole; when the key therefore, is applied, it must of course encounter these interior projections, and its extremity being notched in exact proportion to the several distances to which the sliders are to be carried, it will, when pressed forward, force the sliders to unequal distances from their bearings, and bring the notches on their exterior projections in a direct line with each other, and parallel with the plate; leaving the barrel at liberty to be carried round by the bit or lever on the key, (see s, Fig. 5,) and which fits for that purpose into the notch on the prominence of the barrel, as explained in the description of Fig. 2, serving at the same time to stop the key at its proper point of pressure. When the key is withdrawn, the sliders of course resume their station by the re-action of the spring, and the barrel returns to its confinement.
It hence appears, that unless the various heights of the surfaces expressed on the point of the key, are exactly proportioned to the several distances to which the sliders must be carried to bring their notches into a direct line with each other, they must remain immoveable; and, as one stroke of a file is sufficient to cause such disproportion as will prove an insurmountable impediment to their motion, I may safely assert, that it is not in art to produce a key, or instrument, by which a Lock, constructed on this principle, can be opened.
Fig. 7, is a plan of a complete Lock, with a part of the cap or covering removed, to shew the original mode of applying this principle of security. The dotted lines on the bolt are the spring and tumbler, situated beneath, and having the same office as in the common Lock. The lever x, which is firmly attached to the barrel, represents the web or bit of an ordinary key, and which being carried round with the barrel, takes hold of the bolt in the notch, which it releases by lifting up the tumbler, and projects or withdraws in its revolution. But as circumstances might, by possibility occur, where ingenuity could gain access to the tumbler and release the bolt without attempting the principle of security, Locks are now fabricated in the manner shewn at Figs. 3 and 8, a method which can only be accomplished on this principle, and which vies in importance with the original invention.
Fig. 8, is a plan of the bolt, of the Lock Fig. 3. The point u, is a pin fixed in the bottom of the barrel, e, e, and which, when the barrel is carried round, moves in the direction of the dotted circle, and of course carries the bolt to and fro, with it. The pin v, is attached to the covering plate, and serves to steady the bolt in its motion. The principle of security is thus made to restrain the bolt without the intervention of any other agent; and the slightest inspection must convince, that no power can move the bolt, but that which also puts in motion the barrel.
Fig. 9, is the appearance of a Drawer Lock in its complete state.
It will be a task indeed of great difficulty, even to a skilful workman, to fit a key to this species of Lock, though its interior face were open to his inspection; for the sliders being raised, by the subjacent spring, to an equal height iv the barrel, present a plane surface; and, consequently, convey no direction, that can be of any use in forming a tally to the irregular surface, which they present, when acting in subjection to the proper key. Unless, therefore, a method be contrived to bring the notches, expressed on the extreme points of the levers, in a direct line with each other, and to retain them in that position, till an exact impression of the irregular surface, which the sliders will then exhibit, can be taken; the workman will, in vain, attempt to fit a key to the Lock or move the bolt. And when it is considered, that this process will be greatly impeded, and may perhaps be entirely frustrated, by the action of the spring: it must appear that great patience and perseverance, as well as ingenuity, will be required, to give any chance of succeeding in the attempt. I do not state this circumstance, as a point essential, or of any importance to the purpose of the Lock, but to prove more clearly, what I have before observed upon its principle and properties: for, if such difficulties occur to a skilful workman, as to render it almost, if not altogether, impracticable, to form a key, when the Lock is open to his inspection, and its parts accessible to his hand; it pretty clearly demonstrates, the impossibility of accomplishing it, when, no part of the movement, can be touched or seen.
It will naturally be imagined by the reader, that the same difficulties, which occur in the formation of a key, in the second instance, must have been experienced by the maker of the Lock; and that, however insuperable they may be to other workmen, they were easily conquered by him. But the contrary is the case. No such difficulties occur in forming the original key; nor is any greater ingenuity exercised in the formation of it, than falls to the share of a common workman: for the key is not fitted to the Lock, but the Lock adapted to the key: and this is effected by means the most simple and easy, that can be imagined. The surfaces, expressed on the point of the key, are worked, as fancy may direct, without any reference to the Lock. The key being so completed, and applied to the surface of the sliders, a gentle pressure will force them to unequal distances from their common station, and sink their extreme points to unequal depths, in the space beneath the plate n, n. Whilst the sliders are in this position, the edge of the plate will mark the precise point at which the notch, on each lever, must be expressed. The notches being cut by this direction, the irregularity which must appear in their disposition when the sliders resume their station, and the inequality of the recesses expressed on the point of the key, will be as a seal, and its impression to each other.
Having thus endeavoured to give a just conception of the principle, I trust it will be perceived that the peculiar security of Locks constructed thereon consists in two points of excellence, namely, The infinitude of their variations, by which the production of correspondent keys is avoided, however great the number of Locks may be, that are manufactured on any given scale[2]. And the property of motion, which precludes all possible means of obtaining an impression of their interior parts, for the purpose of fabricating false keys. The former is capable of demonstration: the latter is self-evident.—The variations by which the production of correspondent keys is avoided, have two sources; the one, arising from the changes that may be made in the disposition of the sliders; the other, from the number of points contained on the projected surface of each slider, by which the position of its notch may in the smallest degree be varied.
The variations producible in the disposition of six figures only are 720, which being progressively multiplied by additional figures, will increase in astonishing degrees, and eventually show that a Lock, containing twelve sliders, will admit of 479,001,600 changes. These being again multiplied by the number of changes which the projected surface of the levers will admit, in the disposition of the notches, their amount will exceed numeration, and may therefore be properly said to be infinite. The slightest inspection of these Locks will at once evince that I do not over-rate the effect of their property of motion, in asserting that it precludes all possible means of obtaining an impression of their interior parts, which is necessary to the fabrication of a false key; for it will be clearly seen that the positions into which the sliders are necessarily forced by the pressure of the key in the operation of opening the Lock can no more be ascertained when the key is withdrawn, than a seal be copied from its impression on a fluid, or the course of a ship be discovered by tracing it on the surface of the waves. But inviolable security is not the only excellence they possess; the simplicity of their principle gives them likewise a great advantage over Locks that are more complicated, in point of duration; for their essential parts being subject to no friction, nor exposed to any possible accident from without, they will be less affected by use, and less liable to stand in need of repair.
The imperfections and defects which are common, in some degree, to all other Locks, being thus remedied; and the principle here adopted being an infallible security against the best directed efforts of the picklock, or any similar instrument of violation; I may, without presumption, lay claim to the credit of having brought the art of Lock-making to that perfection which hath been long sought, but which hitherto hath been sought in vain.
It is presumed, that what has been already advanced, has clearly acquainted the attentive reader with the principle and properties of the invention which it is the object of this short treatise to explain; it may not however be unnecessary to introduce a concise review of the advantages afforded by this new principle, which are as follows: viz.
1st. The use of the pick-lock is totally and effectually excluded.
2nd. No instrument but that which is an exact duplicate of the key can have the capacity of opening the Lock.
3rd. There is no possibility of obtaining the form of the key by impression.
4th. The Lock, in principle, is capable of infinite variation, so that Locks may be made with component parts of precisely the same dimensions to the most remote period of futurity, without a duplicate of any former one, and arranged for one key to pass the whole. This property of transposition which supercedes all apprehension from false keys and the property of motion upon which the complete security of the Lock depends, are illustrated by the subjoined Table, in which the first column shews the number of sliders in each Lock. Column 2nd., the number of transpositions. Column 3rd., the variations which may be made in any Lock, supposing the projected surface of each slider to admit of only six different situations for the notch, by which the actual sum of security compared with unity is demonstrated for any given number of sliders, from 4 to 18.
- ↑ We believe some alteration has been made in the construction of these Locks since the first Publication of this Pamphlet.E. D.
- ↑ The value of this property is inestimable, in the case of street-door Locks: for no method of robbery is more practised, than gaining admittance into houses by these keys; which (as is well known) may be procured at the old iron shops, to fit almost any Lock in use.
TABLE.
| 1. | 2. | 3. |
| 40 | 024 | 576 |
| 50 | 0120 | 3000 |
| 60 | 0720 | 25920 |
| 70 | 05040 | 211680 |
| 80 | 040320 | 1935360 |
| 90 | 0362880 | 19595520 |
| 100 | 03628800 | 217728000 |
| 110 | 039916800 | 2634508800 |
| 120 | 0479001600 | 34488115200 |
| 130 | 06227020800 | 485707622400 |
| 140 | 087178291200 | 7322976460800 |
| 150 | 01307674368000 | 11769693120000 |
| 160 | 020922789888000 | 2008587829248000 |
| 170 | 0355687428096000 | 36280117665792000 |
| 00180 | 06402373705728000 | 678651612807168000 |
FINIS.
T. COLLINS, PRINTER,
37, Great Saint Andrew Street, Seven Dials.
Bramah’s Patent Lock
Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Fig. 8
Fig. 9
Engraved by E. Turrell.
This work was published before January 1, 1929, and is in the public domain worldwide because the author died at least 100 years ago.
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