taking a path on the outside of them, which is unavoidably left for a passage for the extremity of the key: complexity in the form of the wards does not, or but very slightly, increase the security, when a picklock is introduced; neither does it generally add to the difficulty of imitating the key, because, in most keys of this sort, nearly two thirds of the metal is superfluous, and requires not to be copied.

According to Mr. Ainger, means of the second sort are the most ancient, having been known in Egypt above 4000 years, as was inferred by M. Denon, from some sculptures on the great temple at Karnac, representing locks similar to those now used in that country, in which means of that sort are employed. The bolt and fixed part of the lock are 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 holes 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 wholly removed into the fixed part. This is effected by a key, having the same number and arrangement of pegs, and of such length that they elevate the ends of the pins in the lock to the place of motion between the bolt and the fixed part. The key is introduced laterally through a long tube, at the end of which it acts vertically upon the pins, whose position, therefore, it is difficult to ascertain.

This principle of security was not generally known in this country, or in Europe, till it was re-invented by Mr. Barron, and applied by him in conjunction with wards to the security of a lock, for which he obtained a patent in 1774. The same principle was afterwards adopted by Mr. Bramah, without the assistance of wards or obstacles to the key; but the mode of application was very different from the Egyptian. In the latter, the security arose from the number and position of the impediments; in Mr. Bramah's, these are discoverable on inspection, and the security depends on the various

degrees of motion which the several impediments require before the bolt can be moved.

These gradual improvements in the fabrication of locks introduced a corresponding degree of attention to the art of picking, which would have been fatal to the reputation of the new locks, had it not been for the almost simultaneous invention of a very simple and cheap alteration, by which the required position of the impediments is rendered undiscoverable.

It was in or about the year 1784, that this new principle was introduced into the art of constructing locks by Mr. Bramah, of Piccadilly,—a name which has subsequently become so identified with the mechanical improvements of our age. Mr. Bramah secured his invention by a patent; and, in a sort of prefatory record attached to the specification, he alludes to the principles of the common locks in use, and then explains the theory of his own. The means previously adopted for the security of all locks are stated to have been, the inserting or fixing, between the keyhole and the bolt, a greater or less number of wheels or wards, which said wheels or wards may be crossed or interwoven in such a manner as to render the communication between the keyhole and the bolt as crooked and irregular as possible, in order to prevent the bolt from being moved by any counterfeit application when the proper key is absent; the bit of which key is so cut or shaped as to form a complete tally with the interior machinery, and be thereby capable of producing the desired effect when applied for the purpose of moving the bolt. According to Mr. Bramah, the insufficiency of this method of rendering locks a perfect security is as follows; viz. notwithstanding the arrangement of these wheels and wards may be so extensively diversified, yet they cannot by any means be sufficiently variable to answer the intended purpose, owing to their being always left fixed in the lock. Their form and disposition can, in almost all cases, be easily obtained by impression; so that, notwithstanding they may prevent the exercise of picklocks,

yet the making a skeleton or surreptitious key is always extremely practicable. And, besides, the variations capable of being made in the disposition of such wheels or wards, and in the form of the key's bit, are not sufficient to produce the required number of locks, without having large quantities exactly alike, and their keys capable of opening one another reciprocally; in consequence of which they become a very imperfect security against violation, as any ill-disposed person might, by furnishing himself with a number of old keys, be enabled to open almost all the common locks in the kingdom with as little difficulty as if he had in his possession the key belonging to each lock.

To remedy these objections by the application of some principle or method whereby the success of picklocks, false keys, and all other counterfeit means of opening locks, might be infallibly prevented, constitutes the claim of Mr. Bramah. In this discovery, the old complication of wards and wheels is done away, and instead thereof, a greater or a less number of movable parts, such as levers, slides, &c., are adapted so as to require each of them a separate and distinct change in their situation and position before the bolt, and other parts of the lock on which its safety depends, can be set at liberty or moved. In the language of the inventor, "these said levers, sliders, or other movables, by the assistance of an elastic, gravitating, or other power, have the property of maintaining or restoring their given position or situation after it may have been destroyed by any forcible application for that purpose. From this said property, the said levers, sliders, or other movables, are rendered capable of receiving (as it were) any impression or required change in their position or situation, correspondent to the cause which produces such said change, and are also thereby always restored to their former state or resting situation, when the said cause is withdrawn, so that the opening of these locks is as difficult as it would be to determine what kind of impression had been made in any fluid, when the cause

of such impression was wholly unknown; or to determine the separate magnitudes of any given number of unequal substances, without being permitted to see them; or to counterfeit the tally of a banker's check, without having either part in possession."

Mr. Bramah proceeds: "The form of these levers, sliders, or other movables, and also the manner of fixing them in the lock, may be varied without end, without altering or losing any of the intended properties or advantages; as the principal merits and efficacy of the invention do no ways depend thereon, but entirely depend on the levers, sliders, &c. being so fixed or disposed as to prevent the bolt, or other parts of the lock on which its safety depends, from being moved, without the said levers, sliders, or other movables first receiving, each of them, a separate and distinct change in their position or situation, by a key or other contrivance for that purpose, which, being pushed against them in a progressive direction, without revolution, occasions them to change their positions in a manner exactly correspondent to the part of the key so applied. And the said part, being formed with a number of irregular surfaces, equal to the number of levers, sliders, &c. against which it is pushed, causes them to move at different times and to different distances from their original situation. And this key, by having a stop or mark to determine the length of its push against the levers, sliders, &c., puts a period to each of their motions, notwithstanding they are at liberty to move farther, but are prevented by the resistance of a spring, gravity, or other power, always endeavouring to restore them to their original situation; so that the motion of each lever, &c. separately depends on the height or depth of the surface of the key against which it falls. Hence a perfect tally is formed, similar to any impression made in a soft body by the forcible application of any harder one; which hard body represents the essential part of the key, and may be of any determinate shape, formed by rule or by accident; and 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 one of them would, by being pushed the least degree too much or too little, entirely prevent the bolt, &c. from being moved or set at liberty. And as the whole of the said levers, sliders, &c. are restored to their resting situation when the key is withdrawn, by the properties or powers above mentioned, the tally or impression is then totally destroyed, and, consequently, the opening of the lock is then left wholly dependent on chance, whilst the said key is absent; as there is no rule whatever, nor imagination founded on certainty, that may, in the least degree, tend to assist in discovering the required position or situation of each or any of the said levers, sliders, or other movables, whereby the form of the key necessary to the opening of the lock might be ascertained.

"Now, admitting," continues the ingenious describer, "that no lock on this principle can be picked, or the form of the key obtained, their farther security then depends on the number of different keys that may be made without having any two of them alike; which number, I trust, will appear indeterminate from the following demonstration, viz.: - 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, &c. be represented by twelve arithmetical progressionals; we find that the ultimate number of changes that may 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