Page:Encyclopædia Britannica, Ninth Edition, v. 14.djvu/770

 746 LOCK you know that it must be at a false notch, and not the true one, for a true one gives no pressure at all. Proceeding in this way, Mr Hobbs opened the challenge lock with eighteen sliders, or guards, which had hung in Messrs Bramah s window for many years, in nineteen hours, and would have done it sooner, but that one of his instruments broke in the lock. He afterwards repeated the operation three times within the hour, in the presence of the arbitrators ; and a more recent one with eight sliders he opened in four minutes, by means of an instrument which is equivalent to a Bramah key with adjustable slits, which are set to the sliders as the operation of feeling them and getting their depths goes on. It is, moreover, to be re membered that thieves do not always confine themselves to the conditions of a challenge, in which force and injury to the lock are of course prohibited ; and, if a lock can be easily opened by tearing out its entrails, it is of very little use to say that it would have defied all the arts of polite lock-picking. In this respect the Bramah lock is singularly deficient ; for if the exposed cap or nozzle of the keyhole is cut off, as it easily may be, or if the hole is widened out by a centre-bit, the sliders can all be pulled oat, and there is an end of the lock. Inside and Outside Locks. Locks for drawers, closets, iron chests, and the like are only required to lock on one side, and their keys are therefore generally made with a pipe, which slips on to a pin in the lock called the drill-pin, and turns on it. Doors which have to be locked sometimes on one side and sometimes on the other cannot have their keys made in this way ; the key is solid, and its plug or stem, being thicker than the flat part or web, acts as an axis fitting into the upper part of the keyhole, though that hole does not completely enclose it. All keys for these inside and outside locks must be symmetrical, or alike on each side of a line through their middle, in order to fit the lock either way, which limits the variety of the tumblers in the case of many-tumblered locks. A Bramah lock, to open on both sides, must be made double, with one set of sliders to push in from one side of the door, and the other set from the other side; and, consequently, they are very seldom used for this purpose, It may be convenient to observe that when we use the term Bramah lock we mean a lock of that construction ; for, the patent having long ago expired, such locks may be made by anybody, only Bramah s name must not be used. Messrs Mordan s locks are the same as Bramah s, except that they make the number of sliders odd, while Messrs Bramah make it even. Letter Locks. At one time it used to be supposed that locks which could only be opened by setting a number of rings or disks to a particular combination of letters could not possibly be opened by anybody who was not in possession of the secret ; and hence they we re also called puzzle-locks. At first they were made with a fixed com bination, which could not be changed. Afterwards the rings were made double, the inner one having the notch in it which the bolt had to pass, and the outer one capable of being fitted on to the inner in any position, by unscrewing some part of the lock, so that you might set them to any combination desired. This was the first instance of a changeable lock, of which we shall have more to say further on. But it was afterwards found that these puzzle -locks have just the same vulnerable point as all our locks had until lately, viz., that the pressure of the bolt can be felt on some of the rings more than on the others ; and Mr Hobbs says emphatically, in the Rudimentary Treatise on Locks, &quot; wherever that is the case, that lock can be picked.&quot; Apart from this defect, these locks have very much gone out of use on account of their being troublesome to handle, and perhaps also from the risk of forgetting the combination to which the lock was set last, if it has been left for some time ; and therefore we do not think it necessary to go farther into the details of their construction. Chubb s Locks. Of the multitude of locks which have been made ou the many-tumbler principle invented by Barren, none enjoyed so much celebrity before Hobbs s as Chubb s. This was partly due to superior workman ship and use of more tumblers than usual, and perhaps still more to the inventor having had the good fortune to hit upon the name &quot; detector &quot; for a certain part of the machinery, which, besides adding to the security against any mode of picking then known, also captivated the public with the idea of discovering if anybody had been tampering with the lock, though the operator might depart in ignorance that he had left any trace of his attempt behind him. It is remarkable that the detector was not even then a new invention ; for a lock exactly the same in principle, but slightly different in arrangement, had been previously made by a Mr Ruxton, and is described in Price s treatise on Locks and Keys, &c., 1856. In the same way false notches were used in Strutt s tumbler lock above thirty years before they were reinvented, by Chubb and others, with the idea of defeating the tentative method of picking by them. In all lever or tumbler locks there is a square pin B, called the stump, rivetted to the bolt, which has to clear the passage in the tumblers called the gating. The original form of Chubb s detector is shown in fig. 16 by the lever DT, which turns on a pin in the middle, and is acted upon at its end T by a spring S, which will evidently allow some play to the lever on either side of the corner X, but the moment it is pushed past that point the spring will carry it further in the same direction, like what is called in clock-work a jumper. In its proper position that end always remains above the turning-point; but, if any one of the tumblers is raised too high, the other end D of the detector, which reaches over all the tumblers, is lifted so far that the end T is sent down below the corner, and the tooth T then falls into a notch in the bolt, and so prevents it from being drawn back, even though all the tumblers are raised properly by the right key, which at once reveals that somebody has been trying to pick the lock. The way to open it then is to turn the key the other way, as if to overlock the bolt ; you observe a short piece of gating near the end of the tumblers, to allow the bolt to advance just far enough to push the tooth of the detector up again by means of its inclination there, and then the lock can be opened as usual. In some more recent locks the tumbler is made in another form. The back tumbler, or the one which has to be raised highest, has a pin d reaching over all the others, and if any of them are overlifted that back tumbler is also, and then a square corner k in it gets past the end of the detector spring ks, and is held up. It is set right by overlooking the bolt as before, the bolt itself raising the end Ic of the spring, and