A secret fastening for doors and similar things, provided with an arrangement of mechanism designed to prevent the introduction or successful operation of any instrument but that which has been made to fit it, called the key: there is consequently a numerous variety of kinds, qualities, and sizes. A good lock has justly been regarded as the masterpiece of smithery. Locks are of great antiquity; according to M. Denon, they were known in Egypt more than 4000 years ago, which he inferred from some sculptures on the great temple at Karnac, representing locks similar to those now used in that country. It would be difficult to trace the earliest introduction of locks into this country; but there is much evidence showing that very curious and secure locks were made many centuries ago. It appears, also, from the celebrated MSS. of "the famous earl of Glamorgan," entitled "A Century of the Names and Scantlings of such Inventions," etc. as he could "call to mind to have tried and perfected," (his notes being lost,) that the art of lock-making was then by no means in its infancy, as he refers to things as if they were then well known which we now regard as important securities to locks; and some of them are commonly considered as being of recent invention.
For these reasons we think it will not be amiss to introduce in this place some of the "scantlings" alluded to. Making some allowance for the quackery of the noble boaster, the reader, who is acquainted with the construction of our modern locks, will recognise much that is now in use to produce similar effects.
"69. A way how a little triangle-screwed key, not weighing a shilling, shall be capable and strong enough to bolt and unbolt round about a great chest, an hundred bolts, through fifty staples, two in each, with a direct contrary motion, and as many more from both sides and ends; and, at the self-same time, shall fasten it to the place beyond a man's natural strength to take it away; and in one and the same turn, both locketh and openeth it."
"71. A key perfectly square, with a screw turning within it, and more conceited than any of the rest, and no heavier than the triangle-screwed key, and doth the same effects."
"72. An escutcheon to be placed before any of these locks with these properties. First, the owner, though a woman, may, with her delicate hand, vary the ways of coming to open the lock ten millions of times beyond the knowledge of the smith that made it, or of me who invented it. Second, if a stranger open it, it setteth an alarum a-going, which the stranger cannot stop from running out; and besides, though none should be within hearing, yet it catcheth his hand as a trap doth a fox; and though far from maiming him, yet it leaveth such a mark behind it as will discover him if suspected; the escutcheon or lock plainly showing what money he hath taken out of the box to a farthing, and how many times opened since the owner had been at it."
"The means of giving security to locks," Mr. Ainger observes, "are of two kinds. The first consists in numerous obstacles (commonly called wards) to the passage of the key, which requires, therefore, a peculiar form to evade them. The second consists in a number of impediments to the motion of the bolt; those impediments being so contrived that their absolute and relative positions must be changed before the bolt can be withdrawn." To these two Mr. Ainger might have added the "rose-turning pipe," and the "secret escutcheon" from the foregoing "scantlings," which also constitute impediments to many modern locks. Means of the first class are defective, because a surreptitious instrument need not thread the mazes of the wards; it escapes them by taking a path outside of them to the bolt, which is unavoidably left for the passage of the extremity of the key. Complexity in the form of the wards, therefore, affords no absolute security against the determined initiated picker of locks, as he can take an impression of the position of the wards, and make an instrument (or skeleton) that will avoid most of them, and take the most direct path to the bolt or its guards. The guards or impediments to the motion of the bolt are called tumblers.
A tumbler usually consists of a small lever, one end of which has a little projection, which latches into a notch cut into the bolt, and is kept down by a spring. It is therefore the business of the key, after it has passed the wards, to raise this tumbler out of the notch entirely before the bolt can be moved, the latter motion being effected by the further motion of the key against a curved portion of the bolt. Great exactness in the length of the bit of the key is therefore necessary to make these parts act properly. If the key be too long, it cannot enter the curved portion, and the tumbler is not reached; and if it be too short, by only the thickness of a sheet of writing paper, the tumbler cannot thereby be lifted quite out of the notch, and the holt is, in consequence, immovable. Sometimes the key has a step or notch which acts upon the tumbler, whilst the other portion of the end of the key acts upon the bolt, which adds to the difficulty of false keys. A single tumbler, therefore, constitutes a certain degree of security, and they are usually applied to locks of a medium quality.
But as this addition to a lock increases the cost about sixpence, the commonest or cheapest locks have no tumbler, the bolt being he.d in the position in which the key puts it by the pressure of a spring. Locks arc, however, made, not only without tumblers, but even without wards, for very common purposes; and being sufficiently secure for their objects, and extremely cheap, they are manufactured in immense quantities, chiefly at Wolverhampton.
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 completely 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's patent cabinet lock does not exceed two shillings; the sale of them is consequently very great.