Rudimentary Treatise on the Construction of Locks

by A. C. Hobbs; George Dodd

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

“Being confident that I have contrived a security which no instrument but its proper key can reach; and which may be so applied as not only to defy the art and ingenuity of the most skilful workman, but to render the utmost force ineffectual, and thereby to secure what is most valued as well from dishonest servants as from the midnight ruffian, I think myself at liberty to declare (what nothing but the discovery of an infallible remedy would justify my disclosing), that all dependence on the inviolable security of locks, even of those which are constructed on the best principle of any in general use, is fallacious. To demonstrate this bold and alarming proposition, I shall first state the common principles which are applied in the art of lock-making; and by describing their operation in instruments differently constructed, prove to my intelligent readers that the best-constructed locks are liable to be secretly opened with great facility; and that the locks in common use are calculated only to induce a false confidence in their effect, and to throw temptation to dishonesty in the way of those who are acquainted with their imperfections, and know their inefficacy to the purpose of security” (p. 5).

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

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

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

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

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

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

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

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