Rudimentary Treatise on the Construction of Locks

by A. C. Hobbs; George Dodd

It is of course natural that each inventor of a new lock should, while describing the product of his ingenuity, point out what he conceives to be the imperfections of locks which have preceded: use has sanctioned the custom not only with regard to locks, but also in other important matters. Hence there have been many “lock controversies” in England during the last seventy years. We have seen how freely and justly the late Mr. Bramah criticised all the locks that preceded his own; and he was certainly not the man to shrink from criticism in his own case. Twenty years ago the Bramah lock was itself made the subject of criticism.

Mr. Ainger, in his lecture on the subject delivered at the Royal Institution, London, and afterwards in his article “Lock” in the Encyclopædia Britannica, thus narrates the circumstances which led to the adoption of the false notches in the Bramah lock as a means of security: “At length (after the original lock had acquired much celebrity,) an advertisement appeared in the public papers, requesting those who had lost keys of Bramah’s locks, not, as had hitherto been done, to break open their doors or drawers, but to apply to the advertiser, who would undertake to save this destructive process by picking. And it appeared that an individual of great dexterity could perform this operation almost with certainty. The effect of this discovery on the demand for the locks may easily be imagined; but the effect it had in stimulating ingenuity to provide a remedy is one of the best illustrations of the proverb, that necessity is the mother of invention. Within a few days or weeks, Mr. Russell, who was at that time employed in Mr. Bramah’s establishment, devised an alteration which at once, and without any expense, entirely overcame the difficulty, and converted the lock into one of perfect security. This contrivance is the most simple and extraordinary that ever effected so important an object; but before we describe it, we will endeavour to explain what has been called the tentative process of lock-picking, and which had been so successfully applied to Bramah’s locks.”

Mr. Ainger illustrates the subject by an engraving—not of an actual lock, but of an hypothetical arrangement of bolts and notches; and he then makes his reasoning apply to the actual process adopted by the picker of the real lock. “A tendency to revolve was given with some force to the barrel; then, by means of a pair of small forceps, the tumblers (sliders) were tried, and it was ascertained which one was most detained by the pressure against the locking-plate. That which offered most resistance was gradually depressed till its notch was felt to hang itself upon the locking-plate; and so on till the whole were depressed in succession, exactly as they would have been depressed simultaneously by the key.” Mr. Ainger then describes the contrivance which, in his judgment, seemed to render any further attempts to pick the Bramah lock hopeless. This consisted in cutting false notches in the sliders; so as to render it impossible for the picker to tell when he has brought a notch to the plane of the locking-plate, whether it is a true notch, or one of shallower depth, unfitted to admit the movement of the plate.

This is a very interesting statement, for it shews that the mechanical or tentative method of opening was known in England long ago, although very little attention has been since paid to it. In a complex Bramah lock, and in locks on the combination principle, the difficulty of picking is almost insuperable, so long as what may be termed the arithmetical method is adopted. It is perfectly true, as has been so often stated, that the varied combinations in the arrangement of the slides amount to millions and even billions, when the slides are in any degree numerous; and if a person attempt to pick the lock by ringing the changes on all these combinations, it would very likely require the lives of a dozen Methuselahs to bring the enterprise to an end. But by the mechanical method, sketched so clearly by Mr. Ainger, the exploit puts on a different aspect. The experimenter passes through the keyhole an instrument so arranged as to give a tendency in the bolt to withdraw in the wished-for direction; and a pressure produced in the slides by this tendency gives information concerning the state of the slides; and then comes the tentative process on the slides themselves. Mr. Ainger was quite right in describing the false notches as an admirable addition to the safety of the Bramah lock; but he was not correct in stating that these notches rendered any further attempts on the lock hopeless. The false notches are not so deep as the true; they will permit the barrel to turn partially but not wholly round. But even supposing that the false notch had been hit upon in nearly every slide instead of the true, and that the barrel had been partially turned to the extent which these notches permitted, there would then be a binding action at the false notches different from that in the true, and this would guide the operator in his search for the true notches. It would not add a new principle different from the one before in action, but it would add to the time during which the search would have to be carried on.

We make these remarks in connection with Mr. Ainger’s article, which was probably written twenty years ago. We now come to the year 1850.

At the meeting of the Institution of Civil Engineers, when Mr. Chubb’s paper was read, many challenges and counter-challenges were made, as to the possibility of picking certain locks. Mr. Chubb described, among others, a lock on the patent of Mr. Davies, which, ingenious though it be, he considers not safe. Captain D. O’Brien differed from Mr. Chubb in this matter; he had had occasion to open from ten to twenty of Davies’s cabinet-locks daily, during a period of two years, and he never once observed the locks to be out of order; in fact, they always appeared to afford great security. Mr. Chubb thereupon rejoined, that he was prepared to produce a workman who would pick any number of Davies’ cabinet-locks, of different combinations, which he had never seen before, taking only half an hour for each lock.

As another instance, Captain O’Brien stated that, in his capacity as Inspector of Government Prisons, his attention had been much directed to the subject of secure locks; and he produced, among others, specimens of those in use at the Pentonville Prison; though not of first-rate workmanship, he characterised them as being safe, strong, and cheap. They were on Thomas’s principle. The locks had been in use eight years, during which period not one had required to be replaced; and any trifling derangements had been made good whilst the prisoners were at exercise. Mr. Chubb, after making his offer concerning Davies’s lock, stated that “he was willing to make the same offer with respect to the locks from the Pentonville Prison; and he might state that, in point of security, he considered them absolutely worthless;” in proof of which he exhibited one of them, and a common burglar’s tool, by which the lock could be opened with the greatest ease.

In respect to Bramah’s lock, there was no particular challenge associated with the proceedings of the evening; but incidental observations were made as to the degree of security pertaining to it. Mr. Farey, after passing a high eulogium on the ingenuity of the principle and the beauty of the workmanship, considered it nevertheless objectionable that the sliders should be so completely exposed to view. He then proceeded to make the following observations: “It had been suggested, that a universal false key for Bramah’s locks might be made, with the bottoms of its several notches formed by as many small steel sliders, extending beyond the handle of the key, so as to receive pressure from the fingers, for moving each one of the sliders within the lock, with a sliding motion in its own groove, independently of the other. During such sliding motion, a gentle force could be exerted, tending to turn the barrel round. Under such circumstances, supposing that the motion of the barrel was prevented by any one slider only; that one, having to resist all the turning force, would be felt to slide more stiffly endways in its groove, and therefore it could be felt when its unlocking notch arrived opposite the steel plate, and left some other slider to begin to resist the turning force. Such a circumstance (continues Mr. Farey) presumes a palpable inaccuracy in the radiating correspondence between the notches in the steel plate and the grooves for the sliders in the barrel, which could not happen with Bramah’s workmanship.”[6] He further remarked: “Unfortunately, if a Bramah’s key fell into dishonest hands, even for a short time, an impression could be easily taken, and a false key as easily made. A turkey-quill, notched into the form of a key, had sufficed to open a Bramah’s lock; and an efficient false key could be formed out of a pocket pencil-case. Such facility of fabrication was an invitation to dishonesty; and as an abortive attempt left no trace, the impunity was an encouragement to repeat the attempt until success is attained.”

[6] See also Mr. Owen’s suggestion, [p. 59], ante.

With respect to Chubb’s locks, a discussion arose out of a statement made by Mr. Hodge. Mr. Chubb had himself stated it to be a general opinion that a skilful workman, furnished with impressions taken from the true key, in wax or soap, could make a false key to open any lock; and he considered that, in common locks, with the most elaborate wards, but with only one tumbler, as also in Bramah’s locks, there was much truth in the notion. In respect to his own lock, however, with six double-acting tumblers, “a false key made ever so carefully from impressions would not be likely to open the lock, for want of exactitude in the lengths of the several steps; and if the key could not be made exact from the impressions, there would be no chance of rectifying it by trial in the lock, on account of the total uncertainty as to which part required alteration.” Mr. Hodge stated that, in America, he had repeatedly seen impressions taken of locks having twelve or fourteen tumblers, in consequence of the bellies of the tumblers, when at rest, coinciding with the form of the key (see [page 63]). He also suggested a method of taking an impression of the bellies of the tumblers; but Mr. Chubb, Mr. Farey, Mr. Stephenson, and Mr. Whitworth, all expressed a disbelief that a Chubb’s lock could be opened by the means indicated by Mr. Hodge. Mr. Hodge admitted that he was not aware of any lock actually made by Messrs. Chubb having been picked in America; but that the locks to which he had adverted were such exact imitations, that he had no doubt of the Chubb lock yielding to similar treatment. He further stated that there were persons in New York who would undertake to pick a real Chubb lock.