1902 Encyclopedia > Lock


LOCK—not being a canal lock—means the fastening of a door, or box, or drawer, which requires a key, or else some secret contrivance or manipulation, to open it. It is generally fixed to the door, but it may also be loose, and then it is called a padlock, which is internally like other locks, but externally has a half link or bow turning on a hinge at one end, while the other, after being put through a chain or staple on the door, enters the lock and is fastened by the bolt therein. The bolt may be moved by the key, or may close by a spriucr, but require a key to open it, as in the. case of handcuffs, which are a pair of padlocks of this kind united by a short chain. A common door lock also comprises a spring latch which opens by. a handle, and sometimes a small bolt held by friction either shut or open, which is moved by asmaller handle inside the room only; but neither of these is the lock proper, any more than a hook or a button, or a common lifting latch. Therefore, omitting them, a lock is as defined above.

The earliest lock of which the construction is known is the Egyptian, which was used four thousand years ago. In fig. 1, aa is the body of the lock, bb the bolt, and cc the key. The three pins p, p, p drop into three holes in the bolt when it is pushed in, and so hold it fast ; and they are raised again by putting in the key through the large hole in the bolt and raising it a little, so that the pins in the key push the locking pins up out of the way of the bolt. The security of this is very small, as it is easy enough to find the places of the pins by pushing in a bit of wood covered with clay or tallow, on which the holes will mark themselves ; and the depth can easily be got by trial.

Mr Chubb, the well-known lock-maker, used to show a wooden Chinese lock very superior to the Egyptian, and, in fact, founded on exactly the same principle as the Bramah lock, which long enjoyed the reputation of being the most secure lock ever invented; for it has sliders or tumblers of different lengths, and cannot be opened unless they are all raised to the proper heights, and no higher. Until about a century ago no lock so good as this was known in England. The locks then in use (fig. 2) were nothing better than a mere bolt, held in its place, either shut or open, by a spring b, which pressed it down, and so held it at either one end or the other of the convex notch aa ; and the only impediment to opening it was the wards which the key had to pass before it could turn in the keyhole. But it was always possible to find the shape of the wards by merely putting in a blank key covered with wax, and pressing it against them; and when this had been done, it was by no means necessary to cut out the key into the complicated form of the wards (such as fig. 3), because no part of thn key does any work except the edge bc farthest from the pipe a ; and so a key of the form fig. 4 will do just as well; and a small collection of skeleton keys, as they are called, of a few different patterns, were all the stock in trade that a lock-picker required.

The common single-tumbler lock (fig. 5) was rather better than this, as it requires two operations instead of one, to open it. The tumbler at turns on a pivot at t, and has a square pin at a, which drops into a notch in the bolt bb, when it is either quite open or quite shut, and the tumbler must be lifted by the key before the bolt can be moved again. But this also is very easy, unless the lock is so made that the tumbler will go into another notch in the bolt if it is lifted too high, as in the. lock we shall now describe, which was the foundation of all the modern improvements in lock-making.

Barron’s Lock.—This was the first lock with several tumblers. It was patented in 1778. Fig. 6 is a front view, and fig. 7 a horizontal section. First consider it with reference to one tumbler at only. Unless the square pin a is lifted by the key to the proper height, and no higher, the bolt cannot move, and that alone adds very considerably to the difficulty of picking, except by a method not discovered for many years after. But Barron added another tumbler, and unless both were raised at once to the proper height, and no higher, the lock could not be opened. The face, or working edge, of the key of a many-tumblered lock assumes this form (fig. 8), the steps corresponding to the different heights to which the tumblers have to be raised, and one of them acting on the bolt, and they may have a much wider range of difference than in this figure. The key here drawn is also one with the wards of such a shape that no skeleton except itself can pass them. The form, however, can be got in the usual way by a wax impression ; and as it weakens the key very much, and is expensive to cut, it is not often used.

Bramah’s Lock.—The next lock of any importance was the celebrated one patented ten years after Barron’s, by Joseph Bramah (see BRAMAH). In figs. 9 and 10 aaaa is the outer barrel of the lock, which is screwed to, or cast with, the plate ; cccc is a cylinder, or inner barrel, turning within the other. It is shown separately at fig. 11; and fig. 12 is a cross section of it, the black ring being the keyhole, and the light spot in the middle the drill-pin, which goes into the key. The short pin b in figs. 9, 10, 11 is set in the end of the cylinder, near its edge; and, when the cylinder turns round, that pin shoots or draws the bolt, by acting in a slit of the form shown in fig. 13. The security of the lock depends upon a number of sliders, s, s, of which the shape is shown in fig. 14, and the cross section in fig. 12. They are made of plates of steel doubled, and sprung open a little, so as to make them move with a little friction in the slits of the cylinder or revolving, barrel in which they lie, and are pressed up against the cap of the lock by a spiral spring. They are shown so pressed up in fig. 9, and pressed down by the key in fig. 10. There is a deep groove cut round the barrel, and in each of the sliders there is a deep notch which can be pushed down to that place in the barrel by a key slit to the proper depth ; and it is evident that when all the sliders are pushed down to that position the barrel will present the appearance of having no sliders on it. A steel plate (fig.15), made in two pieces in order to get it on, embraces the barrel at the place where the groove is, having notches in it corresponding to the sliders, and is fixed to the body of the lock by two screws marked d, d in figs. 9, 10, and 15. When the sliders are pushed up by the spring they fill the notches in the plate, and prevent the barrel from turning ; but when they are pushed down by the key the notches in the sliders all lie in the plane of the plate, and so the barrel can turn with the key, and the pin b in the end of it drives the bolt as before described. The key has a bit, k, sticking out from the pipe, the use of which is to fix the depth to which it is to be pushed in, and then, as the bit slips under the cap of the lock, it keeps the key at the same depth while it is being turned.

This was the construction of the lock for a good many years, and Bramah pronounced it in that state "not to be within the range of art to produce a key, or other instrument, by which a lock on this principle can be opened." It was found, however, long before the defeat of the improved challenge Bramah lock by Mr Hobbes in 1851, that the inventor had made the common mistake of pronouncing that to be impossible which he only did not see how to do himself. As it has been generally supposed that what is called the tentative method of lock-picking was unknown in England before it came over from America in the year of the Exhibition of 1851, we must remind our readers that it was described in the 7th edition of this work fifty years ago, though the lock-picking fraternity were not of sufficiently literary habits to make themselves acquainted with it. Mr Hobbs, it is true, carried the process further than had been supposed possible before ; but all the Barron and Chubb and other many-tumblered locks, which were supposed impregnable, might Iong ago have been opened by anybody who had paid attention to the method by which the Bramah locks were known to have been picked some seventy years ago, before the introduction of the false notches designed in 1817 by Mr Russell, then one of Mr Bramah’s workmen. If you apply backward pressure to the bolt of a tumbler lock when locked, or twisting pressure to the barrel of a Bramah lock, first pressing down the spiral spring, there will be a greater pressure felt against some of the tumblers or sliders than against others, in consequence of inevitable inequalities of workmanship; and if you keep the pressure up, and gently move any of the tumblers or sliders on which the pressure is felt, you will at last get it to some point where it feels loose. That may or may not be the exact place to which the key ought to lift it ; but as soon as you feel it loose leave it alone, it will not fall again, as the friction is sufficient to prevent it ; and, if necessary, you may fix it there by a proper instrument, or measure the depth and keep the measure till you begin again. Then try another tumbler which feels tight, and raise it till it also feels loose. And if you go on in that way, always leaving the loose tumblers alone, and raising the one which feels tight, they will at last all be got into the position of complete freedom, i.e., to the place where the stump of the bolt can pass them. The operation is just the same in principle in the Bramah lock and in tumbler locks; only, as all the sliders are acted oil by one spring in the Bramah as now made, you need only just push down that spring, and hold it there, and then the sliders may be moved freely either way by means of a hook or a small pair of self-acting forceps to pull them up if they accidentally get pushed too far. At first each slider had a separate spring.

But if the sliders have some false notches in them not so deep as the true ones (see fig, 14), and the corners of the notches in the plate dd are cut out a little (as in flg. 15), then you might by trial get all the sliders into such a position that the barrel could turn a very little, but no more ; and when it is turned that little, you cannot push the sliders in any further, and so (as was long supposed) the tentative process is defeated; and undoubtedly it is made much more troublesome, but it only requires more time and patience. You can still feel that the pressure is greater against some one or more of the tumblers or sliders than against others, and, wherever that is that is the case, 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 remembered 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 out, 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 flue 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 have the number of sliders odd, whereas Messrs Bramah’s have it even.

Combination Lock.—In this class of lock, known also as permutation, letter, or puzzle locks, a prearranged combination of letters or figures engraved on an external disk has to be brought against an index before the bolt or locking apparatus can be liberated. In early forms each lock answered only to a single combination, and when that combination was known the lock became useless. Subsequently the locks were made so that the combination could be varied at will; but in England the apparatus was regarded as little better than a toy, troublesome to work, and risky to the owner, who might forget the figures or letters to which he set his lock. Combination locks have, however, come into large use in America for safes and strong rooms. The modern combination lock has enclosed within its case a series of disks free to move on a common centre. When it is set to a particular combination of figures engraved on the disks themselves, the notch in each disk can only be brought into a position for freeing the bolt by bringing the consecutive figures on the movable disk outside the door successively in line with a marked point on the rim which surrounds the disk. A lock with three disks graduated to 100 each gives a million possible combinations, and, having no opening nor keyhole, it cannot be blown up by explosives. Combination locks are made in America by tho Yale Company, Hall’s Safe and Lock Company, and others.

Chubb’s Locks.—Of the multitude of locks which have been made on the many-tumbler principle invented by Barron, none enjoyed so much celebrity before Hobbs’s as Chubb’s. This was partly due to superior workmanship and use of more tumblers than usual, and perhaps still more to the inventor having had the good fortune to hit upon the name "detector" 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 overlocking the bolt as before, the bolt itself raising the end k of the spring, and letting the tumbler fall. This form of detector is, however, inferior to the other, as it informs the picker what he has done, by the back tumbler itself being held up, which he can feel directly.

But since Mr Hobbs’s mode of picking locks became known all these detectors have become useless. Some persons have even gone so far as to say that the detector may be made a guide, to picking. Whether this be so or not, the detector does not act unless some of the tumblers are raised too high, which they never are by a skilful operator on this plan, nor does it act (even if thrown by accident) against picking backwards, or feeling the way to shoot the bolt a little further, as if to free the detector; and in this way the measure of the key can be taken without any hindrance from the detector. Before 1851 tumbler locks were seldom made with false notches, except Strutt’s, in which the tumblers were in the form of quadrants, with a very large angular motion, and a number of short or false notches and one deep one. But after that year Chubb and other makers of tumbler locks adopted false notches, too,ether with revolving curtains, which cover the straight part of the keyhole as soon as the key is turned, and barrels going down from the back of the curtain to prevent a false key or pick from turning without turning the curtain ; other obstacles were added, of which the object is in all cases to prevent the maintaining of pressure of the stump upon the tumblers at the same time that the tumblers themselves are moved, or, as Mr Hobbs called it, tickled, by some other instrument. These provisions undoubtedly make the locks more difficult to pick, but it is by no means safe to assume that a lock will never be picked, merely because it would take a first-rate hand a long time to do it or gradually make his key.

Hobbs’s Lock.—The invention which most directly meets the defect of all previous locks is Mr Hobbs’s "movable stump," which is not rivetted into the bolt as usual, but is set on the end b of a bent lever abc (fig. 17) which lies in a hollow of the bolt A behind it turning on a pivot in the bolt itself, and kept steady by a small friction-spring e. The stump comes through a hole in the bolt, large enough to let it have a little play and the long end a of the lever stands just above the edge of a square pin d, which is fixed in the back plate of the lock When the lock is locked, if you push the bolt back, you produce no sensible pressure on the tumblers, but only just ehough to turn this protector lever, as Mr Hobbs calls it, on its pivot c, and so bring down its end a in front of the square pin, and then the bolt can no more be pushed back than when held by Chubb’s detector. The protector is set free again by merely pushing the bolt forward with the key, without reference to the tumblers. It was found, however, that in this state the protector could be prevented from acting by a method used by the inventor himself for another purpose, viz., pushing a piece of watch-spring through the keyhole, and up behind the bolt, so as to reach the protector at a, and keep it up while you push the bolt back, or, again, by pushing up the watch-spring be-tween any two of the tumblers, and holding the end b of the protector with it, so as to press the stump against the tumblers. Both these devices, however, are prevented now by letting in a feather FF in a groove between the bolt and the back of the lock, which no watch-spring can pass, and also bringing a piece of the feather forward through the front gating of the tumblers just under the stump. In this form the lock is safe against any mode of picking at present known, unless the keyhole happens to be large enough to admit tho inspecting method, which is this. A person intending to pick the lock goes beforehand and smokes the bellies, or lower edges of the tumblers, through the keyhole. When the key comes, it wipes off the black on each tumbler, according to the length of the bit which raises it; and then, when the picker returns, he throws a strong light into the keyhole, and, by means of a narrow reflector put into it, reads off, as it were, the length of bit required to raise each tumbler to the proper height. This operation may sound impossible ; but it is an established method of lock-picking in America. It requires a largish keyhole however, and it niay be prevented by any kind of revolving cylinder which will conceal the view of the tumblers while the keyhole is open. The inspecting method might also be frustrated by making the acting part of the bellies of all the tumblers no longer than would be reached by the shortest bit in the key. In that case, the long bits would not begin to act at their points, but on their sides, and would leave no measure of their length upon the tumblers.

A multitude of other many-tumbler locks acted on by springs, and with various kinds of detectors and revolving curtains, all more or less upon the same principles, may be seen described in Price’s book above-mentioned, but we are not aware that any of them have ever come into general use, or are superior to Chubb’s or equal to Hobbs’s protector locks. There is another group of locks which involve fanciful and thick ugly keys, and for that or other reasons have not got much beyond patents and exhibitions. "Revolving curtains" have been proved to be less serious impediments to picking than they would seem, inasmuch as they must leave room for an instrument no thicker than the key itself to turn. The only kind of curtain that is not open to this objection must be one that absolutely prevents any touching of the bolt while any instrument at all is within the lock, and projects at all outside. Mr Hobbs accomplished that by the odd-looking contrivance of a key consisting only of its web, or flat or acting part, which is pushed into the lock, and then carried round by a fixed handle in another place, which closes the keyhole until it has come round again and delivered the key-web ready to be taken out by a proper hook. But this was too troublesome for common use. The same object is effected in another way by Sir E. Beckett’s lock, which we shall presently describe.

Tucker’s Locks.—There have been several locks on the disk principle invented in succession by Mr Tucker of Fleet Street, London, the first two of which had revolving disks ; and in the last and more simple one, patented in 1855, though the disks no longer revolve, they slide between fixed plates without springs, and do not turn on a pin like common tumblers, and will stand in differently anywhere. It will be sufficient to describe the last of these inventions, as Mr Tucker himself states it to possess all the elements, of security of the former ones, with the advantages of being much cheaper, because more simple in construction. In fig. 18 TT is one of the sliders, which are separated by thin fixed plates, and slide upon the guide-pins at TT, and have also friction-springs X pressing on them to keep 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 confusion). 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 bave 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, tehc urtain alone being cast with the barrel and bit P on it, and its face turned, which is a cheaper operation than filling. In this respect it approches 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 he has abolished the use of the file, and left nothing to hand labour excpet 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 unnecessary 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 cupboards, 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 horizoatal, 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.

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 than usual to resist all attempts to force the shackle open of them involve any novelty in principle, and they are all capable of being dealth with in the same way; and therefore we shall at once pass on to another class of clocks, viz., those which shut of themselves, and 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, ofteh 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 generally used for a lock which shuts of itself on a box or drawer, or articles of that kind ; and the latter for street or room-door locks which shut of themselves, and open with a handle on the inside, but only with a key on the outside. In the simplest and cheapest form of these locks there is no pretence of any security except a few fixed wards, which the key has to pass; and, as before explained, that is no security at all against anybody with the smallest dexterity, and with a serious intention of opening the lock. Next to them, or rather below them, pretending to be what they are not, come the locks which lock a certain distance themselves by means of a spring, but can be locked further by the, key, and have tumblers, but no fixed wards (which a good tumbler-lock does not require). But though this kind of lock cannot be opened when it is thus double locked, except by the key, or some efficient mode of picking, yet when they are only self-locked the tumblers are of no more use than if they did not exist, and the lock can be opened by any bit of bent wire that will go into the keyhole. It should be remarked, however, that the Bramah lock is just as secure as usual when used for a spring or latch lock, because the key cannot turn at all without pushing in the sliders properly. But in this, as in all latch-locks, it is very unsafe to have a handle which pulls back, as it can easily be reached by a wire put through a hole in the door; the handle should always be made to turn, like a common room-a or handle.

There are two ways in which spring-locks with tumblers are made as safe as the same lock with an ordinary bolt. One is to make a click or catch fall into the bolt when it is drawn back, and not to make the tumblers to fall when the bolt is drawn back ; in the shutting of the door this catch is pushed back by some knob projecting for the purpose, and then the tumblers fall and hold it fast. Prison locks are made in that way. But this will not do for a latch-lock which is intended to open by a handle on one side of the door. For that purpose the proper plan is that which is now adopted in all good latch and spring locks, not to let the key act directly on the bolt, which has no stump, but on the false bolt which lies on the top of the real one, and has the stump fixed in it. When the real bolt is shut by the spring it carries the false one with it, and that is then locked by the tumblers. But the real bolt can be pushed back by the door shutting, or pulled back by the handle, without moving the false bolt, though it cannot be reached through the keyhole. In buying a lock, the test of this is to see whether the stump moves as you push or pull the bolt back. If it does the lock is good for nothing, unless it is on some other peculiar construction.

Latches and Latch Locks.—The latter of these, so called by Mr Chubb, is substantially on the principle just now described, and so is Hobbs’s and Hart’s latch lock, which also has the protector stump, and therefore is as unpickable as their other locks, provided neither the handle nor the bolt can be got at. Chubb’s latch (not his latch-lock) consists only of four tumblers, which come out and form the bolt and fit between a sort of mouth in the striking-plate on the door post, and have all to be lifted to the same height by the key; but that can easily be picked by the tentative method, though it might delay a common street thief for an inconvenient time.

Spring Curtain.—All latch locks for street doors are liable to stick fast through dirt getting between the tumblers, especially in a smoky town. They will keep clean much longer if the keyhole is protected by Sir E. Beckett’s self-acting spring curtain, which can be added to any lock which is worth it. It consists only of a small thin steel plate, sliding on the key-pin, and another pin just below the keyhole to guide it, with a slight spring behind, for which there is room in any latch lock with a sliding locking plate over the bolt. They are not patented, and the cost is quite insignificant, and it is odd they are not more commonly insisted on by purchasers.

Safe Locks with Small Keys.—In all the locks we have yet mentioned the bolt is acted on by the key, even thoug h the key may not touch it; the key must therefore be strong enough to move the bolt besides lifting the tumblers, or whatever is substituted for them, and this makes the key for a large lock too large and heavy to be conveniently carried in the pocket, and a bunch of such keys impossible. To get over this difficulty, most of the makers of iron safes have adopted the plan (we do not know by whom invented) of shooting, a large bolt, or a number of bolts, by means of a handle, and then a small lock with a small key locks into one of them, and thus fastens them all. The security then depends upon the impregnability of the small lock against fraudulent picking or forcible evisceration. There are certain thieves' instruments by which a force sufficient to tear open the inside of a lock can be inserted through a keyhole of the common size. This, however, is now defeated by cutting out a piece of the back plate, and then screwing it on again with only a few small screws and so that alone gives way under any bursting pressure, whether from the instrument called the jack-in-tbe-box, or f rom gunpowder, which is another of the thieves' methods for cutting the knot which they cannot untie. If the small lock, therefore, cannot be picked, or forced, this mode of locking the bolts of a large door is quite safe, and you have the advantage of a very powerful lock with nothing to carry in your pocket larger than a small desk key.

Sir E. Beckett’s Lock.—A lock was invented by Sir Edmund Beckett (formerly Denison) in 1852, but not patented, which combines the advantages of large and strong works with a keyhole so narrow that no instrument strong enough to injure the lock could be got in, nor a reflector to observe the bellies of the tumblers; and the bolt is not only shot by turning the handle, but locked besides, without using any key at all. This lock enjoys the distinction of being the only one of English invention which was pronounced secure against any known method of picking, by Messrs Hobbs and Tomlinson, in the treatise before referred to.

In fig. 20 are shown the tumblers T, turning on a pin at or near the middle of their length. so as to be nearly balanced, though in small locks this is unnecessary. Between every two adjacent tumblers, and between the bolt and the tumbler next to it, there is a thin steel plate, which occupies the position shown by the dotted lines PP. These plates have one edge lying against the upper side of the lock, so that they cannot turn at all on the tumblerpin, which goes through them quite loosely. One or two of the plates should be bent a little to make them act as friction springs on the tumblers when the cap of the lock is on, so that they will stand indifferently in any position. In the figure they are drawn all pressed down, so as to prevent the stump S from entering the gating, and this has been done by the long, tail Y of the handle, which, it is easy to see, will raise the left end of the tumblers, and depress the right, after the fan-tailed piece X of the handle has shut the bolt. After the tumblers have been raised to the proper height by turning the key half round (where it may be stopped by the plates P, P), the stump can enter the gatings, and the bolt can be drawn back by the handle, the tail Y then doing nothing. So far as we have yet gone, the lock would possess no greater security than any other many-tumblered lock; but there is a steel curtain CC, which does not revolve as usual, but slides on two pins set in the back of the lock, and is pressed up against the front plate by two spiral springs, so as to close the keyhole completely, except when it is pressed in. From the back of the curtain there goes a kind of square plug (shown in section at fig. 21), which can be pushed through a hole in the back plate, and has a notch in it just in the plane of the bolt, and the bolt itself has a corner there; in this way, when the curtain is up, the bolt can be drawn back through the notch in the curtain plug; but when the plug is pushed in ever so little the bolt cannot be drawn back, because its corner cannot pass the curtain plug, and in this position the stump cannot be made to touch the tumblers, except one of them, which is made a little longer than the rest (as shown at T in fig. 20), in order to keep the bolt steady. It is evident then that as soon as the curtain is pushed in, to admit any instrument whatever, the bolt is held fast, and it becomes impossible to put any pressure of the stump upon the tumblers; in other words, the tentative mode of picking is impossible. In small locks the curtain has no plug, but merely works against the edge of a second stump f the bolt, which can only pass when the curtain is up, and it slides on the drill-pin and another pin below it.

The security of the lock is farther increased by the addition (DEG) of what may be called a detector, as it does detect if the bolt has not been shot far enough by the person who locked it, and, what is of more consequence, prevents it from being opened in that state. It turns on a hinge or pin at G, and is held up or down by a jumperspring at E, as in Chubb’s first detector. In fig. 20 it is shown as held down, or out of the way of the bolt; but, as the handle turns back again and draws back the bolt, the pin below X raises the detector a little, and then the spring is ready to throw its tooth into the notch in the bolt as soon as it is shot only about half-way. In that state the bolt cannot be drawn back without turning the handle far enough for the fan-tail X to send the detector down again below the corner of the spring, and by doing that you will also have locked all the tumblers, and so made the lock fast until the key comes to open it. And it is to be observed that the curtain cannot be pushed in until the bolt is fully sbot, so that no exploration of the lock can take place while it sa open, or even partially open. By adding a spring catch under the curtain, to be freed by one of the tumblers when it is fully locked, it may be arranged, if required, that the curtain could not be pushed in, not only until the bolt is shot, but until the tumblers are locked also.

The following, therefore, are the advantages of this lock. 1. A very large lock, with all its parts strong, Only requires a very small key, not weighing above a quarter of an ounce. 2. No key is required to lock it, and you cannot leave the key in the lock (a fruitful source of mischief), and yet it is free from the inconvenience of spring-locks. which sometimes shut themselves when not intended, and moreover, when large, require large and strong keys to open them. 3. It cannot get out of order from the usual causes of the tumblers sticking together, or tumbler-springs breaking, because there are none, and the tumblers do not touch each other, but the friction-plates between them. 4. The keyhole being always quite closed by the curtain, except while the key is in, the lock is protected from dirt and from. the effects of a damp or smoky atmosphere, which injures other locks. 5. The smallness of the keyhole prevents the insertion of any instrument strong enough to force the lock, and also prevents inspection. 6. It is pronounced by the highest authority to be secure against any known mode of picking. 7. It requires no delicacy of construction or high finish in any of the parts, and the moving parts are few—in fact, the whole of then together are fewer than the number of springs alone in the great American lock of Day & Newell. 8. It is free from the incum brance of a patent, the inventor being one of those who agree with the opinion of the jury on philosophical instruments in the exhibition of 1851, and with many of the first engineers and most scientific men, that "patents are a great obstruction to the progress of science," and waste, on the whole, more money than they gain for real inventors.

Changeable Key Locks

Any lock with many tumblers may be changed by taking it off and, transposing any two or more of the tumblers; but it will then want a different key, and the process is too troublesome to be resorted to except when there is reason to apprehend that the original key has fallen into bad hands, or had a copy taken of it. A lock which can be locked by a great number of keys, but can only be opened by the one which locked it last, is evidently an immense addition to security. Those keys may either be all distinct, or there may be a great number of different webs, or stepped parts, fitting to a common handle ; or each bit or step may be separate, and all screwed together into the key frame as shown in fig 22.

In a lock with n tumblers, each raisable to m distinct heights, if you have only n loose bits of the m different heights you may compose 1 x 2 x 3 . . . . n keys, which for nine tumblers=362,880. But if you also have m bits for each place in the web, the possible number of different keys is very much greater, viz., mn ; for every possible length of bit in each place may be used with every possible length in every other place. If m is 7 and n 9, as they are in the locks we are going to describe next, each lock may have very nearly sixty million different keys, or key-webs capable of fitting into one shank or handle ; and the chances are so many against a lock-picker hitting on the right one.

The first changeable key lock known in England was Day & Newell’s "Parautoptic" (in spection-defying) lock, which was brought from America by Mr Hobbs at the time of the 1851 Exhibition, and has been largely used since for banks and other safes. It was fully described in the last edition of this work, and in the books above referred to; but in this place we will describe instead a much simpler form of it, since introduced by Mr Hart of the firm of Hobbs, Hart, & Co. The principle of all changeable key locks is that instead of a single stump fixed to the bolt, there are as many stumps as tumblers, and each one is the projecting part S of a slider PPS which can ride up and down on two pins PP in the bolt, and will stay at any height, where it is left when the bolt B

is shot. Fig. 23 shows theolock open end the slider stumps lying in the jaws or gating of the tumblers ready to be raised to any height. In fig. 21 the bolt has been shot, and the sliders carried forward with it. Just before they leave the tumblers they are received by the two small teeth C, C on the frame of the lock, holding each slider at whatever height it may then be ; those teeth go right down to the thin part of the bolt or as deep as the sum of all the tumblers and sliders. In this figure the topmost slider is received at its third notch, and each of those below it at some other notch. The tumblers having fallen behind all the stumps, the sliders cannot move until the tumblers are all raised again to the various heights at which they left them, which is possible only by the key that locked the lock. These locks, have Hobbs’s protector behind the bolt ; and the bit which moves the bolt is behind a revolving curtain (the darkest circle) which is kept steady by one of the tumblers resting on its flattened top. The bellies of the tumblers are shortened, to obviate a certain trick by which one of Newell’s locks was picked, but which it is not necessary now to explain. So far as we can judge, this lock has more than all the advantages of that, as it is much less complicated and liable to get out of order from any cause except that to which all locks with spring tumblers are liable, viz., from two tumblers getting stuck together by dirt, so that one of them rises too high with its neighbour. Oiling tumblers is accordingly fatal to them, though it is necessary in other parts of a lock.

The keys of these locks are practically made not of distinct bits screwed into a key frame as in fig. 22, which is the plan used in the Day & Newell lock, and makes a heavy thing to carry, but separate webs are made, each complete in itself, and fitting into a thickish key pipe which need not be carried about. You may leave it near the safe, and lock up therein, or keep somewhere else, all the bits except the one you use for the day, and carry that in your waistcoat pocket. For such a lock as that described you may have as many of the sixty million bits as you like, and may get new ones from time to time. Or you may have separate bits, as in the parautoptic lock, but in that case you must take good care of the key whenever the lock is shut.

Yale Lock

This American lock is remarkable for the smallness of its key, which is shown from k to a in fig. 25, full size, and is a thin flat piece of steel weighing only 1 of an ounce. The narrowness of the keyhole would be an impediment to introducing a picking instrument together with any other in tended at the same time to give a twisting pressure to the small barrel abc, which has to turn, as in the Bramah lock, in order to move the bolt, which is not shown in these figures. That may be done either as in Bramah locks or by a tongue or bit attached to the end ab of the barrel as in several other locks. The barrel is prevented from being turned, except by the proper key, thus. The (apparently) five plugs with spiral springs over them in fig. 25 are really all divided at the cross line bc, being all now lifted to the proper height by the key. Consequently the barrel abc can turn round, as there is no plug either projecting from it or projecting into it. But when the key is out, all the plugs are pushed down by the springs, and so the upper ones descend into the barrel and hold it fast. And again, if any of the steps of a false key are too high, some of tho lower plugs will be pushed up beyond the barrel into the holes above them, and so the barrel cannot turn. The bevelled end of the key near a enables it to be pushed in under the plugs, though with some friction and resistance. In recent forms of the Yale lock the blade, of the key is corrugated throughout its entire length, and the key-hole and key chamber are correspondingly contoured. This corrugation renders it absolutely impossible for any picking instrument to be introduced to raise the, pins and release the revolving barrel, seeing that no up-and-down motion is possible to the picking instrument. A Yale lock of seven pins has ten millions of possible combinations.

Time Locks.—These are keyless combinations which permit of the opening of lock-fast places only at intervals fixed before the closing of the door. They are controlled by clock-work set in motion within the lock-case, and the machinery automatically releases the bolt or frees a separate lock at the hour, and for the interval, to which the clock or clocks have been set. The Yale timelock contains two chronometer movements which revolve two dial plates studded with twenty-four pins to represent the twenty-four hours of the day. These pins, when pushed in, form a track on which run. rollers supporting the lever which secures the bolt or locking agency, but when they are drawn out the track is broken, the rollers fall down, and the bolt is released. By pulling out the day pins, say from 9 till 4, the door is automatically prepared for opening between these hours, and at 4 it again of itself locks up. For keeping the repository closed over Sundays and holidays, a subsidiary segment or track is brought into play by which a period of twenty-four hours is added to the locked interval. Careful provision is made against the eventuality of running down or accidental stoppage of the clock motion, by which the rightful owner might be as seriously incommoded as the burglar. In the Yale lock, just before the chronometers run out, a trigger is released which depresses the lever by which the bolt is held in position. In the Holmes electric time lock all electric attachment is brought into play should the chronometers cease to act, and thereby the movement is kept up till the hour for which the clocks were set when the bolt is released. Several thousands of time locks are in use in America; and to some extent they have been introduced in the United Kingdom. (E. B.)

The above article was written by Edmund Beckett, the Right Hon. Lord Grimthorpe, K.C., LL.D.; author of works on clocks, architecture and astronomy.

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