In 1774 a great improvement in the art of lock-making in this country was made by Barron, who took out a patent for it; it consisted in the employment of two or more tumblers, of the same construction as the single one before described, but so arranged that they must be operated upon at different times, or altogether, and be moved through different spaces, so as to take them com pletely out of their notches, and set the bolt free to be acted upon. The proper key has therefore a number of steps at the end of the bit, exactly adapted to move the tumblers through the required spaces; and as this arrangement admits of almost endless variations, and is extremely simple in itself, very beautiful and secure locks have continued to be manufactured on the principle ever since it was brought before the public. The facilities of "getting them up" are now so great at Wolverhampton and Birmingham, by the application of machinery for fabricating the separate parts of these (as well as other) locks, chiefly by stamping, that the wholesale price of a good Barron'a patent cabinet lock does not exceed two shillings; the sale of them is consequently very great.
Although no doubt can be entertained that Barron really invented the lock we have been noticing, it appears from the statements of Mr. Ainger. that the Egyptian locks now in use are constructed upon the same principle as Bar ron's ; and as these modern Egyptian locks are the same as those observed upon the great temple at Karnac, the invention which we have been regarding as our countryman s, and of modern date, is upwards of 4000 years old. The bolt and a fixed part of the Egyptian lock are, as described by Mr. Ainger, each pierced with any number of holes, arranged in any chosen form ; those in the bolt and in the fixed part coinciding when the bolt is locked. These bolts are occupied by pins, which are contained in the fixed part, and descend into the bolt, so as to prevent its motion till they are removed wholly into the fixed part. This is effected by a key having the same number and arrangement of pins, and of such a length, that they elevate the ends of the pins in the lock to the plane of motion between the bolt and the fixed part. This key is intro duced laterally through a long tube, at the end of which it acts vertically upon the pins, whose position therefore it is difficult to ascertain. The same prin ciple was afterwards adopted by Mr. Bramah, (who took out a patent for it in 1784,) but without the assistance of wards ; his mode of application was, however, very different from the Egyptian. In the latter the security arose from a concealment of the number and position of the impediments; in Mr. Bramah's these were discoverable on inspection, and the security depended on the various degrees of motion which the several impediments required before the bolt could be moved. 'The office which-in ordinary locks is performed by the extreme point of the key, is, in Bramah's, assigned to a lever, which cannot approach the bolt till every part of the lock has undergone a change of position. The lock may be described as consisting of a common axis, on which six levers, crossing the face of the lock, are united as in a joint. Each of these rests upon a separate spring, sufficiently strong to bear its weight, or if depressed by a superior force, to restore it to its proper position when that force is removed. The levers pass through a frame by separate grooves, exactly fitted to their width, but of sufficient depth to allow them a free motion in a perpendicular direction. The joint or carriage of the levers, and the springs on which they rest, are fixed on a circular platform, turning on a centre, and the motion of this platform impels the bolt in either direction by means of a lever. The inviolable restraint upon this lock, by which means it is eubjected only to the action of the key, is lodged in 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 block on which it rests. By this plate the motion of the machine is checked or guided in the following manner:—on the edge of the plate which faces the movement there are six notches, which receive the ends of the levers projecting beyond the frame ; and while they are confined in this manner, the motion of the machine is so totally suspended u to defy every power of art to overcome. To understand in what manner the proper key of this lock over these obstacles, it must be observed that each lever has a notch on its• extremity, and that those notches are disposed as irregularly as possible. To give the machine a capacity of motioo, these notches must be brought parallel to each other, and, by a distinct but unequal pressure upon the levers, be formed into a groove in a direct line with the edge of the plate, 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 con trolling the power of the springs, will give liberty to the levers to move in s horizontal direction, as far as the space between the blocks which support the plate will admit, and which is sufficient to give the machine the power of acting on the bolt. The key exhibits six different surfaces, against which the levers are progressively admitted in the operation of opening the lock : the irregu larity of these surfaces shows the unequal and distinct degree of pressure which each lever requires to bring them to their proper bearings, in order to put the machine in motion. Hence it appears that unless the various heights of the
surfaces expressed on the bit of the key are exactly proportioned to the several distances necessary to bring the notches into a straight line with each other, they must remain unmovable: On this principle it would be a matter of great difficulty for any workman, however skilful, to construct a key for the lock when open to his inspection ; for the levers, being raised by the subjacent springs to an equal height in the frame, present a plane surface, and, conse 5nenfiy, 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 key. Unless therefore we can contrive a method to bring the notches in the 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 be unable to fit a key to the lock, or to move the bolt. If such difficulties occur even when the lock is open to the inspection of a skilful workman, much more must we'suppose it out of the power of one who has not access to the internal parts to make a false key. These difficulties render it necessary in making locks of this kind not to fit the key to the lock, but to fit the lock to the key. The key must therefore be made first, and the inequalities upon the surface of the bit worked as chance or fancy may direct, without any reference to the lock. The key being thus completed and applied to the surface of the levers, will, by a gentle pressure., force them to unequal distances from their common station in the frame, and sink their points to unequal depths into the space beneath the plate. While the levers 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 appears when the levers resume their station in the frame, and the inequality of the recesses on the bit of the key, will appear as a seal and its corresponding impression. The moving of the bolt, or other parts of the lock whereby it may be opened, entirely depends on the positive motion of the levers, &c., as any of them would, by being pushed the least degree too much or too entirely prevent the bolt from being moved or set at liberty : and as the whole of the levers are restored to their situation when the bolt is withdrawn, the tally, or impression, is totally destroyed, and, consequently, the opening of the lock is left wholly dependent on chance whilst the said key is absent, as there is no rule whatever to assist in discovering the required posi tion of each or any of the levers, or other movables, whereby the form of the key necessary to the oyening of the lock might be ascertained. Mr. Bramah calculated the number of changes of position that the levers of such a lock are capable of before the right one might be discovered, in the following manner :— " Let us suppose the number of levers, sliders, or other movables, by which the lock is kept shut, to consist of twelve, all of which must receive a different and distinct change in their position or situation by the application of the key, and each of them likewise capable of receiving more or less than its due, either of which would be sufficient to prevent the intended effect; it remains, therefore, to estimate the number producible, which may be thus attempted :—Let the denominations of these levers, &a be represented by twelve arithmetical pro gressional', we find that the ultimate number of changes that pay be made in their place or situation, is 479,001,500; and by adding one more to that number of levers, &c., they would then be capable of receiving a number of changes equal to 6,227,019,500, and so on progressively, by the addition of others in like manner, to infinity. From this it appears that one lock, consisting of thir teen of the above-mentioned levers, sliders, or other movable parts, may (by changing their places only, without any difference in motion or size) be made to require the said immense number of keys, by which the lock could only be opened under all its variations." Statements like the foregoing, apparently founded upon just reasoning, obtained for Bramah's patent an extraordinary degree of reputation, and, for the patentee, during many years, a very lucrative trade ; but this and other improvements induced a corresponding study in the art of picking, which finally obtained a triumph over Bramab's invention ; and had it not been for the dis covery of new means of baffling the picker's art, by the introduction of false notches, the reputation of these admirable locks would have been destroyed ; but, from the apparent impossibility of discovering the false from the true notches, or of ascertaining those which assist from those which do not assist in the effect the lock is now deemed inviolable ; it is manufactured very exten sively, and sold at very moderate prices.