Page:Encyclopædia Britannica, Ninth Edition, v. 14.djvu/772

748 LOCK

them steady. S is the bolt stump, which can only enter I, the gating of the tumblers, when they are pushed the proper distance towards the left, which the key will do as soon as it turns towards the left, in the usual way of unlocking. But something else still prevents the bolt from falling, and that is the flat curtain C, which turns with the key, and has also a barrel B, as in several of the other locks we have spoken of. This curtain prevents the stump from being pressed against the tumblers, being just big enough to keep it from touching them until it has turned nearly three quarters round, when the pin S, which stands up on the stump, can enter the opening D in the curtain (shown by a dotted line in the drawing, to prevent con fusion). But by the time the curtain has got so far round, any instrument in the keyhole would be prevented by the barrel from reaching the tumblers so as to push them back and feel the pressure of the stump; at least so the inventor asserts, and we do not venture to contradict him; but it must be remembered that no revolving curtain and barrel have yet been able to prevent the instruments of the American lock-pickers from reaching and moving the tumblers at the same time that the barrel is being pressed the other way in order to keep up pressure on the bolt. We have not yet explained how the bolt in this lock is drawn back when the curtain has got into the proper position for it. It is not done by the last bit in the key acting directly on the bolt as usual, but by a bit P fixed on the curtain itself, which acts upon the notch B in the bolt, as the key usually does. And this same bit P performs another function in locking, viz., shooting all the tumblers into the position here shown by striking against a pin which is set in the bottom one, and comes up to the curtain, and so carries all the others with it by means of the square notch which is cut in all of them, except the one which has the pin in it. It must be observed that the curtain does not lie close upon the tumblers, but there is the thickness of the bolt, or of the bit P, between them. A spring locks into the curtain and prevents it from being turned, except when this spring is pressed down by putting a key into the keyhole. One object of making the curtain, and not the key, to lock and unlock the bolt is that you guard against the risk of what is called short-locking, i.e., sending the bolt in any common tumber-lock not quite far enough for the tumblers to drop. There are means by which a person intending afterwards to pick a lock might cause it to lock short, if he had previous access to it, or possession of the key, at least as locks are generally made, and then, of course, he has only to pull the bolt back, the tumblers having never fallen. Moreover, this arrangement in Tucker's lock allows it to be locked by any key that will turn in the keyhole, though it cannot be unlocked by any but the true key, or one which will move all the tumblers to the right place for the stump to enter them. Mr Tucker has also applied the curtain in his padlocks in such a way that the shackle has a tail reaching inwards and resting against the curtain at all times, except when it is in the proper position for opening, i.e., when this tail is opposite to a segment cut out of the curtain corresponding to the opening D in the lock just now described, but much larger. The object of this is to obtain greater strength than usual to resist all attempts to force the shackle open. The cheapness of these locks is due to the circumstance that all the principal parts can be stamped out of sheet brass, the curtain alone being cast with the barrel and bit P on it, and its face turned, which is a cheaper operation than filing. In this respect it approaches to Mr Hobbs's style of lock-making; only he has carried the stamping and machine-finishing system much further; indeed, it is hardly exaggerating to say that he has abolished the use of the file, and left nothing to hand labour except the mere fitting

of the pieces together, and putting the tumblers in the right position to have the gating cut according to the key.

Nettlefold's Bolt. – We have already alluded to padlocks, and we shall do so no farther, because they are generally of exactly the same internal construction as other locks of the same maker. And, for the same reason, it is unneces sary to describe the various modifications of the fastening part of locks to adapt them to peculiar uses or positions; but there is one which does seem to be worth a short notice, viz., an invention of Mr Nettlefold, patented in 1839, for making the bolt hook into the striking plate, against which it locks. Fig. 19 will explain the nature of the contrivance at once. We have inserted no tumblers, because it may be used with one kind of lock as well as another. It is convenient for writing-desks, sliding cup boards, and even for drawers, which can often be prized open by merely putting in a screwdriver above the lock, and forcing up the piece over it just enough to let the bolt, which is generally short, pass. There are other ways of doing the same thing, such as making the bolt itself hooked, and giving it two motions, first vertical, to shoot it out, and then horizontal, to hook it into the striking plate; and some Bramah locks are made with a kind of annular bolt, which forms a rim to the cylinder, with a segment cut off in one place to let the striking plate come down, which is then taken hold of by the other part of the ring as it revolves. Bramah locks of portfolios, and articles of that kind, are usually made in this way, which is very cheap and simple.

Fig. 19.

Master-Keys. – It is often convenient to have a set of locks so arranged that the key of one will open none of the others, and yet the owner of the whole may have one master-key that will open them all. In the old locks with fixed wards this was done by making the wards of a slightly different form, and yet such that one skeleton will pass them all, just as the skeleton-key in fig. 4 will serve for the warded key of fig. 3, and a multitude of others. In locks with sliders or tumblers, the way is to make one tumbler in each lock with a wider gating, so as not to require lifting so high as it does in the other locks of the set; then the key of that lock will raise that tumbler in that lock high enough to clear the stump, and yet the master-key, which has a longer bit in that place, will not raise it too high, because the gating is wide enough for both; but the special key of that lock will not open any other of the set which has not the same tumbler widened in the gating. Mr Chubb, many years ago, made a set of locks for the Westminster Bridewell, with keys for the different grades of officers. The owner of the head key can stop out any of the under keys; and if any attempt is made to pick any lock, and the detector is thrown, it cannot be released by any of the subordinate keys, though they can open the lock in its normal state, and consequently the governor must be acquainted with it. There are a variety of other forms of many-tumblered locks, but none of them involve any novelty in principle, and they are all capable of being dealt with in the same way; and there fore we shall at once pass on to another class of locks, viz., those which shut of themselves, and are called –

Spring or Latch Locks. – These locks we chiefly notice because they require a particular provision to make them in the smallest degree secure, and are, nevertheless, often left without it, by way of saving a shilling or two in their price, and multitudes of street-door robberies are committed in consequence. The former of these two names is