# A Dissertation on the Construction of Locks (1785)

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A
Dissertation
on the
Construction
of
Locks.
A
Dissertation
on the
Construction
of
Locks.
Containing,
By Joseph Bramah.
London:
Printed for the Author. Sold by R. Baldwin, Pater-Noster-Row.
A
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. The art and invention of ingenious men have in all times been applied to contrive means of ſecurity adapted to the particular dangers to which either life or property were expoſed, from 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 hath yet been offered to the world, which the ingenuity of wickedneſs hath not found 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, which are practiſed in the ſcience of robbing, may be effectually counteracted. Modern depradation 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 which are made to juſtice, without lamenting the ineffectual ſeverity of the law; and earneſtly withing 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 which it excites in the unpracticed 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 to prevent acceſs to them by every poſſible ſecurity, ſeems therefore to promiſe more towards leſſening the number of robberies, which bring daily diſgrace on the police, and diſturb the peace of the cities of London and Weſtminſter, 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 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 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 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.—Having diſpatched this part of my ſubject, I ſhall proceed to the ſpecification of a Lock, which by great application and expence, I have completed, and now offer to 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 judgement and teſtimony will do credit to the inventor, by confirming the efficacy, the infallibility, and the originality of the invention.
The principle on which all 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 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 outworks 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 hath 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 pipe, 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 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 hath 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 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 ſubſtract 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, and beyond all compariſon, more excellent and more ſecure, than any Lock 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, and as ſenſible as I am 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 fortification of the bolt, by a new and 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 in Mr. Baron’s Lock the caſe is otherwiſe. He hath not only improved upon the practiſed method of applying the tumbler, but hath given it an office which is perfectly new, and of more importance to its ſecurity, than any impediment which art can oppoſe to the introduction of a falſe key. Inſtead of leaving his tumblers liable to be forced to an indefinite diſtance from the point at which they ceaſe to controul the bolt; he hath confined 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. This ſpace or groove, is, in form, an oblong ſquare, and is not only furniſhed with niches on the under ſide, into which the hooks of the tumblers are forced by the ſpring as in other Locks, but is ​provided likewiſe with correſpondent niches on the upper ſide, 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 degree of 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 ſkill and 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 hath not yet ​attained that point of excellence in the conſtruction of his Lock, which is eſſential to perfect ſecurity.—His improvement hath greatly 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 talents and ability; and, becauſe (if ſuch were his intentions) he did not ​overrate 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 intreat 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 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 moft 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 to fifty, muft 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 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. 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 lofs 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 introduction of ſolid wards ​may therefore be more properly termed an alteration, than an improvement in the art of Lock-making.
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 pretenſion. 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. It ſeems, therefore, that the ſole property of this invention might have remained with the projector without a patent.
I could add many reaſons to thoſe I have given, in proof of my original poſition, “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.”—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 to 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 imputed to, and pointed out in the principle, or the conſtruction of all other Locks, are not effectually remedied in that which I preſume to offer 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 be more deſerving 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, that 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 in at leaſt an equal degree, with the contrivances which mechanical ingenuity hath invented and applied for ſecurity. And this evil hath 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; 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 his leiſure. But, practicable as I conceived this to be, I did not venture to attempt it by any means, which had hitherto been found ineffectual. I had not the preſumption to imagine, that I could give perfection to an inſtrument, which men of much greater knowledge and ability, had left defective. I was, therefore, as ſollicitous to avoid their excellences, as to eſcape their imperfections, which, are ſo blended in the beſt Locks, as to make it impoſſible to adopt the ​one, without falling into the other. And a very little thought on the ſubject, convinced me, that my 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 my 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. 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, therefore, which in other Locks is performed by the extreme point of the key, is here aſſigned to a lever, which cannot approach the bolt till every part of the Lock hath 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.
Among the various methods of applying the principle of motion, in the conſtruction of Locks, which have yet occurred in my practice, I think thoſe, deſcribed in the ſubjoined plates, are to be preferred, for their ſimplicity.
The firſt plate ſhows the interior face of a Lock, which was conſtructed, at a very early period of my experiment, and was intended merely as a model, to try the efficacy
Plate 1$^{st.}$ :
* F
​of the principle; but, to my great admiration, it turned out a complete inſtrument of ſecurity; and gave the cleareſt demonſtration, that the principle was certain and infallible.
SPECIFICATION.
Plate the firſt.—The lines, which croſs the face of the Lock, repreſent ſix levers, which are united in a joint, and turn on a common axis, at the point A. Each lever reſts on a ſeparate ſpring, of ſufficient ſtrength to ſuſtain its weight, or, if depreſſed by a ſuperior force, to reſtore it to its proper poſition, when that force is withdrawn. The curve B repreſents a frame, through which the levers are carried by ſeparate grooves, or paſſages; theſe grooves are exactly fitted in their width, to the thickneſs of the levers, but are of ſufficient length, to allow them a free motion, in a perpendicular direction, ​whether lifted by the elaſtic power of the ſprings, on which they reſt; or ſunk by the preſſure of a ſuperior weight from above. The part, which projects from the oppoſite ſide of the joint, or carriage, A, and inſerts its extreme point in the bolt, at C, is a lever of a different form, which acts in ſubordination to thoſe above deſcribed; to this lever, two offices are aſſigned, the one to keep the bolt in a fixed, and immoveable poſition, in the abſence of the key;—the other to give it its proper motion, when the key is applied. The joint, or carriage of the levers, and the ſprings on which the levers bear, are fixed on a circular platform, D, which turns on a center; and in its motion impels the bolt, in either direction, by means of the lever, which is projected from the joint A.—To give this machine the property of inviolable ſecurity, it was neceſſary to ſubject its motion to ſome reſtraint, which the key only could remove. This power is lodged in the ​part E, which is a thin plate, bearing at each extremity on a block, and having of courſe a vacant ſpace beneath, equal in height, to the thickneſs of the blocks on which it reſts. This plate is applied either to check, or to guide the motion of the machine; and theſe oppoſite offices are thus performed.—On the edge of the plate, which faces the movement, ſix notches are expreſſed, into which the points of the levers, projecting beyond the frame B, are received; and whilſt they are ſo confined, the motion of the machine is totally ſuſpended, and the bolt ſo fixed, as to defy every effort of art, or force, to move it.—The neceſſity of the proper key, to the purpoſe of opening this Lock; and the impoſſibility of effecting it by other means, will be clearly ſeen from the proceſs, by which the machine is put in motion. It is to be obſerved, that each lever has a notch expreſſed on its extreme point; and, that thoſe notches are diſpoſed as ​irregularly as poſſible. To give a capacity of motion to the machine, theſe notches muſt be brought parallel to each other, and, by a diſtinct, and unequal preſſure upon the levers, be formed into a groove, in a direct line with the edge of the plate E, which, the notches are exactly fitted to receive. The leaſt motion of the machine, whilſt the levers are in this poſition, will introduce the edge of the plate into the groove; which, controling the power of the ſprings, will give liberty to the levers to move in an horizontal direction, as far as the ſpace between the blocks, which ſupport the plate E, will admit, and which is ſufficient to give the machine a power of acting on the bolt.—The impoſſibility of thus bringing the notches, expreſſed on the points of the levers, to fall into a direct line, and to form a groove, which ſhall perfectly tally with the edge of the plate E, 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, which is repreſented by the figure F, exhibits ſix different ſurfaces on its bit, againſt which the levers are progreſſively admitted, in the operation of opening the Lock; the irregularity of theſe ſurfaces deſcribes the diſtinct, and unequal degree of preſſure, which each lever requires to bring them to their proper bearings, for the purpoſe of putting the machine in motion. It hence appears, that unleſs the various heights of the ſurfaces, expreſſed on the bit of the key, are exactly proportioned to the ſeveral diſtances, to which the levers 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.
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 levers being raiſed, by the ſubjacent ſprings, to an equal height in the frame B, 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 levers will then exhibit, can be taken; the workman will, in vain, attempt to fit a key to the Lock; or, by any effort of art, to 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 ſprings; it muſt appear that great patience and perſeverance, as well as great 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 a mean the moſt ſimple, and the moſt eaſy, that can be imagined. The ſurfaces, expreſſed on the bit of the key, are worked, as chance, or fancy, may direct; without any reference to the Lock. The key being ſo completed, and applied to the ſurface of the levers; a gentle preſſure will force them to unequal diſtances from their common ſtation in the frame B; and, ſink their extreme points to unequal depths, into the ſpace beneath the plate E. Whilſt the levers are in this poſition, the edge of the plate E, will mark the preciſe point at which the notch, on each lever, muſt be expreſſed.
Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Fig. 8
​The notches being cut by this direction, the irregularity, which muſt appear in their diſpoſition, when the levers reſume their ſtation in the frame B; and, the inequality of the receſſes, expreſſed on the bit of the key; will be as a ſeal, and its impreſſion to each other.
Having endeavoured (and I hope with effect) to give a juſt conception of the Principle, and to prove, that inviolable, ſecurity infallibly reſults from the moſt ſimple application of it; I ſhall proceed to give an example of its effect, in a Lock more curiouſly conſtructed, and, in which it is more extenſively applied.
The firſt figure of the ſecond plate, repreſents a circular block of metal, divided from its center into eight compartments; each compartment containing a cell, which forms a paſſage through the block, as repreſented by the ſmall circles, deſcribed on the flat ſurface A.—In each of theſe cells, ​two grooves are cut at oppoſite points, which open a communication with the center at one point; and with the ſpherical ſurface of the block, or barrel, at the other.—The ſmall circle, which marks the center of the flat ſurface A, is the key-hole, which likewiſe forms a paſſage through the barrel, in a parallel line with the cells, which ſurround it.—This figure repreſents the frame, in which, the parts that compoſe the active principle of the Lock, are depoſited.—To render the operation of theſe parts, and their reſpective offices perfectly intelligible, they are both individually, and collectively, repreſented on the plate.
The ſecond figure deſcribes a ſpiral ſpring, which is lodged in the bottom of each cell, and occupies one half of its ſpace. The other half is filled with a ſlider, which reſts on the ſpring, and is repreſented by the third figure. The office of theſe ſliders, exactly correſponds with that of the levers, ​in the model above deſcribed: for, when lodged in their reſpective cells, they are upheld, like the levers, by the elaſtic power of the ſprings on which they reſt; till a preſſure ſuperior to that power is applied;—and are again reſtored to their ſtations by the reaction of the ſprings, when the weight, which depreſſed them, is withdrawn. Each ſlider projects its ſide B (as appears in the fifth figure) beyond the ſpherical ſurface of the barrel, or frame, which contains it; as the extreme points of the levers (in the above model,) are projected beyond the curved frame, in which they move. The point C is projected through the interior groove, into the ſpace which forms the center, or key-hole, expreſſed on the flat ſurface A.—When the key, therefore (which the fourth figure repreſents,) is applied, it muſt of courſe encounter theſe interior projections; and when preſſed forward, (the ſpaces indented on its point being unequal,) will force the ſliders ​to unequal diſtances from their bearings; and bring the notches, expreſſed on their exterior projections, in a direct line with each other; in the ſame manner, and for the ſame purpoſes, that a ſimilar effect is produced, by the preſſure of the key upon the levers, in the model above deſcribed, for it is to be obſerved, that the diſpoſition of the notches in this, as in the former inſtance, is marked, while the ſliders are under the preſſure of the key. When the key, therefore, is withdrawn, and the ſliders reſume their ſtation in the cells, through the action of the ſprings, the diſpoſition of the notches muſt be irregular, in the ſame proportion and degree, that the indentures on the point of the key are unequal: and they will neceſſarily fall again into a direct line with each other, whenever the ſliders are depreſſed by the key.
The fifth figure repreſents the barrel, or frame, completely furniſhed and fitted for ​action. The interior end of the barrel, is capped with a plate, which, unites its compartments, and confines the ſprings and ſliders, within their reſpective cells. From that plate the point A proceeds; which repreſents the lever by which the bolt is projected, or withdrawn, according to the direction in which the machine performs its revolution.
The ſixth figure, repreſents the flat ſurface of a thin plate; which correſponds in its office with the part C, deſcribed in the ſpecification of the model. The ſpace, cut in its center, is exactly fitted to the ſpherical ſurface of the barrel;—the circle, deſcribing its circumference;—and the notches cut on its edge, coinciding with the projections of the ſliders. The barrel, being encircled by this plate, at the middle of its ſpherical ſurface, its motion is entirely ſuſpended; till the notches, expreſſed on the projections of the ſliders, are forced by the preſſure of the key, into a line with each other:—a groove being ​thus formed on the ſpherical ſurface of the barrel,—parallel to, and coinciding with, the edge of the plate; the machine is at liberty to perform a revolution, in either direction, as its office may require; but returns to its confinement, when the key is withdrawn.
The component parts of the movement, being thus united, the interior end of the barrel is depoſited in a bed, which the ſeventh figure repreſents; and to which it is faſtened at the angles of the plate (figure 6) by which the barrel is encircled. The ſtation of the bolt is at A.—The lever, which acts upon it in the revolution of the barrel, is projected on the oppoſite ſide.
The eighth figure is a cap, or maſk, which incloſes the face of the movement, and completes the Lock.
The peculiar ſecurity of Locks, conſtructed on this principle, conſiſts in two points of excellence, which no other Lock poſſeſſes; 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. 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 levers;—the other, from the number of points, contained on the projected ſurface of each lever, by which the ​poſition of its notch may, in the ſmalleſt degree, be varied.
The variations, produceable in the diſpoſition of ſix figures only, are 720; theſe, being progreſſively multiplied by additional figures; will increaſe, by aſtoniſhing degrees; and eventually ſhow, that a Lock, containing twelve levers, will admit of 479,001,500 changes; which, the addition of another lever will increaſe to 6,227,019,500.—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 ​cleanly ſeen, that the poſitions, into which the levers 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. And being determined, that nothing on my part ſhall be wanting, to render the improvement univerſally beneficial; I have no difficulty in pledging myſelf, to thoſe who may be induced to honour me with their commands; that I will no further avail myſelf of my patent, than to ſecure the property of the invention; and that every kind of Lock, conſtructed on the above ſpecification; ſhall be delivered at a price, as low as the expence of manufacturing, with the addition of a very ſmall profit, will admit.
THE END.
NEW INVENTIONS, of which JOSEPH BRAMAH is the Author, Patentee, and ſole Proprietor.
N. B. Orders for the above Articles, from any Part of the World, will be faithfully, and punctually executed at his Manufactory, No. 14, at the Weſt End of Piccadilly.
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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