A Lock may be defined to be any kind of fastening which is intended not to be opened except by one particular instrument, called the key, or by some secret method of manipulation. The earliest lock of which the construction is known is the Egyptian, which was used 4000 years ago. In this drawing (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, has shown us a wooden Chinese lock which is 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 eighty years ago, we had no lock so good as this 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 you could always find the shape of the wards by merely putting in a blank key covered with wax, and pressing it against them; and when you had done so, 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 that key does any work except the edge 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 would require.

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 \(bb\), either when it is 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, and which is the foundation of all the modern improvements in lock-making.

Barron's Lock.—Fig. 6 is a front view, and fig. 7 a Barron's horizontal section, of Barron's lock, which was patented in the year 1778. First consider it with reference to one tumbler, \(at\), only. You see that 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 besides that, Mr Barron added another tumbler, and unless both were raised at once to the proper height, and no higher, the lock could not be opened. We are not aware that Barron himself ever went beyond two tumblers; but the principle of the many-tumbleder lock is undoubtedly his, and nothing that was added to it for nearly eighty years afterwards made any material addition to its security. But instead of making a separate pin to each tumbler, and a corresponding number of notches in the bolt, the simpler plan was adopted by other makers of putting what is called the gating, in the tumblers, and a single pin in the bolt, which is then called the stamp; this will be shown presently in the drawing of Chubb's still more famous lock. The face, or working edge, of the key of a many-tumbleder 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 Bramah's the celebrated lock originally patented, just ten years after Lock, Barron's, by the late Mr Joseph Bramah, who came up to London from Barley as a joiner, and raised himself to eminence by the invention of this lock, of the machine for numbering bank-notes, the beer-engine, the water-closet, the pencil-cases called "ever-pointed," and, above all, the hydraulic press—an invention which, like Nasmyth's steam hammer, extended the powers of man beyond what before had been conceived possible. In figures 9 and 10, \(aaa\) is the outer barrel of the lock, which is screwed to, or Bramah's 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, x, 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 in 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, as every one knows who has seen a Bramah 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 you are turning it.

This was the construction of the lock for a good many years, and Mr. 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. Hobbs 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 here before it came over from America in the year of the great Exhibition, we must remind our readers that it was described in the last edition of this work nearly thirty years ago; though, no less fortunately than strangely, the lock-picking fraternity were not of sufficiently literary habits to make themselves acquainted with it. Mr. Hobbs, it is true, carried the process farther than had been supposed possible before; but all the Barrow and Chubb, and other many-numbered locks, which were supposed impregnable, might long 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 forty years ago, before the introduction of the false notches, designed by Mr. Russell in 1817, 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 Bramah's Lock.

The place where the stump of the bolt can pass through. The operation is just the same in principle in the Bramah lock and in tumbler locks; only, as all the sliders are acted on 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 do not cut out a little (as in fig. 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 farther, 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 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 we have seen him open a more recent one with eight sliders 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 he goes on feeling them and getting their depths. It has been stated as an advantage of the Bramah lock, that an impression cannot be taken from it. This is a great mistake. Mr Chubb showed us a small instrument, which a man could hold in his hand without it being seen, and by which an exact impression of the depths of any Bramah key, whose number of slits is known beforehand, can be taken in a moment, and the other end of the instrument then becomes a key which will open the lock at once.

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; and in this respect the Bramah lock is singularly deficient; for if the exposed cap or nozzle of the key-hole is cut off, as it easily may be, or the hole widened out by a centre-bit, the sliders can all be pulled out, and there is an end of the lock. But, as a protection against picking by pressure without violence, Mr E. B. Denison suggested an alteration, of which a specimen was made in 1853 by Messrs Mordan (who are now the largest manufacturers of Bramah locks), on the principle of Mr Hobbs's moveable stump for tumbler locks. The locking-plate is not screwed to the body of the lock, but is left free to turn a little; and if it is turned by putting any pressure on it from the sliders, it pushes a click CC (fig. 16) into a notch in the barrel and holds it fast, and so no pressure of the sliders can be felt. In this case, the locking-plate is made in one piece, and the barrel in two. If that contrivance had existed in Messrs Bramah's challenge-lock, it could not have been picked by Mr Hobbs's method. However, locks for securing property well worth stealing must be safe against rude as well as polite lock-picking, and this the Bramah lock hardly can be made; and therefore it must be admitted, that, even with the above-mentioned improvement, it is now behind the requirements of the age, though the smallness of the key, and the cheapness with which they can be manufactured and sold to the trade (though they are not yet sold by retail as cheap as some other better locks), will probably enable them to keep their place for some time.

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 made with a pipe, which slips on to, and turns on a pin in the lock, called the drill-pin. But doors which have to be locked sometimes on one side, and sometimes on the other, cannot have their keys made in this way; but the key is solid, and its plug or stem being thicker than the flat part or web, it acts as an axis fitting into the upper part of the key-hole, though that hole does not completely inclose 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-tumbled 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, they may be made by anybody, just as Chubb's lock may, though nobody but the representatives of the original patentees has a right to apply the name Bramah or Chubb to them; and therefore Messrs Mordan, for instance, rightly call them by their own name, though their locks are the same as Bramah's, except that they generally make the number of sliders odd, while Messrs Bramah make it even.

Cotterill's Lock.—The lock of Mr Cotterill of Birmingham is on the same principle as Bramah's, the difference Lock, being, that the sliders are pushed out radially by a very thick key with inclined slits in it. The locking-plate is a ring instead of a flat plate, and the notches in the sliders have all to be brought into the same circle, to be able to pass along the ring. Some of the sliders are made into what are called detectors, being held by a spring catch, if they are pushed out too far. This is the primary form of Cotterill's lock; and in that form it is evidently quite as easy to pick as the commonest form of Bramah lock, and easier, because the range of the sliders is necessarily very small, as the extreme range can be no more than the thickness (not the diameter). Cotterill's of the key-pipe. But Mr Cotterill afterwards added a second ring X (fig. 17) outside the fixed locking-ring RR; and in that outer ring you observe that the notches are not quite opposite to the ends of the sliders, some of which are bevelled; and therefore, when pushed out by the key, they will force themselves into the notches of the outer ring, and turn it a little against the resistance of a spring, which tends to keep it in the position shown in the drawing with reference to the cylinders and sliders. When it is so pushed a little out of the way by the bevelled sliders, the square-ended ones can enter the holes then opposite to them, and so carry their own notches into the position to pass the inner or fixed ring, and then the cylinder can turn, and it carries the outer ring with it. Moreover, in the latest form of this lock, the inner ring is not absolutely fixed, but has a little play, like the plate of the improved Bramah lock in fig. 16; and by the side of it there is a click, CC, which any slight turning of the ring brings into action, and makes it lock the ring fast. This appears, from Mr Cotterill's description and drawing, to be just the same contrivance which we have already described as being applied by Mr Denison to the Bramah lock to prevent feeling the pressure of the sliders on the locking-plate; only this appears to lock into the ring itself, and therefore would not prevent the pressure from being felt; whereas Mr Denison's click for the Bramah lock fastens the barrel, and does prevent the pressure. But that could easily be done in the same way in Mr Cotterill's lock; and, if so done, it would, as far as we can see, be of much more value than the second ring, as we shall explain presently. The entrails of this lock could not be taken out, like Bramah's, by merely cutting off the nozzle.

This lock acquired some celebrity, from having defeated Mr Hobbs in a challenge to pick it. But from the printed account of the affair, sent to us by Mr Cotterill himself, it is clear that that failure proved nothing, except that Mr Hobbs was taken by surprise, and supposed that he was picking one of Cotterill's locks as they had been made before the invention of the second ring, and such as he had publicly exhibited a mode of picking with merely a piece of wood; whereas the lock in the trial contained these other arrangements, which Mr Hobbs knew nothing of. It is certainly added, in the printed account, that, when he did see the additions, he confessed that he did not then see how such a lock was to be picked, and declined to try it. Whether it really is invincible in its present state we are not able to say, not professing to be lock-pickers ourselves; but it does appear to us that the inventor considerably overstates the difficulty when he says all the sliders must be moved together; for it seems plain that pushing out any two nearly opposite sliders with the bevelled ends would turn the outer ring as well as a dozen; and as soon as it is turned a little it is of no further use. No doubt all the sliders must be at last brought together into the proper position, as they must in any other lock; but that is a very different thing from requiring them all to move simultaneously into that position. And whether the lock is impregnable or not, we should imagine that the great thickness and weight of the key, which is necessary to get even a moderate range in the sliders, would generally be considered an objection to it, as we have the best authority for saying, that in some other cases the highest amount of supposed security will not induce even bankers to adopt locks with large keys.

Letter Locks.—It used to be supposed, some years ago, that locks which could only be opened by setting a number of rings or discs to a particular combination of letters could not possibly be opened by anybody who was not in possession of the secret; and hence they were also called puzzle-locks. At first they were made with a fixed combination, 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 you like. This was the first instance of a changeable lock, of which we shall have more to say at the end of this article. 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, "wherever that is the case, that lock can be picked." We have heard an amusing account of his opening, in a few minutes, a great dial lock on an iron door at Liverpool; and also opening a French lock in the Great Exhibition, and setting it to a new combination, so that the exhibitor himself could not open it. Besides 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 it was set last, if the lock has been left for some time; and therefore we do not think it necessary to go further into the details of their construction; the principle of it we have described sufficiently to make it intelligible.

Chubb's Locks.—Of the multitude of locks which have Chubb's been made on the many-tumbler principle, originally invented by Barron, none have enjoyed so much celebrity as Chubb's, partly from their superior workmanship and use of more tumblers than usual, and perhaps still more from the late Mr Chubb, or his brother, who took out their first patent in 1818, 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. In the same way false notches were used in Strutt's tumbler lock above thirty years before they were re-invented by Chubb and others, with the idea of defeating the tentative method of picking by them. The original form of this invention is shown in fig. 18 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 farther 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 a little, i.e., 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 Mr Chubb's 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 reaching over all the others, and if any of them are overlifted, that back tumbler is also, and then a square corner & in it gets past the end of the detector spring &s, and is held up. It is set right by overlocking the bolt as before, the bolt itself raising the end & 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 farther, as if to free the detector; and in this way, at any rate, the measure of the key can be taken without any hindrance from the detector. Before 1851 tumbler locks were seldom made with false notches; we remember, however, seeing a lock on an iron door, invented by Mr Strutt many years ago, 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 since that year Mr Chubb and some other makers of tumbler locks have adopted false notches in all their best locks, together with revolving curtains, which cover the straight part of the key-hole 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; and other obstacles, 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 has called it, tickled, by some other instrument. These provisions, and especially a number of small false notches (which may be got with a thick stump by serrating the end of it), undoubtedly make the locks much more difficult to pick; in fact so difficult, and requiring such nicety of instruments and manipulation, that they may be considered practically safe, except under extraordinary circumstances. But then it must be remembered that all the great robberies, of which there are several every year, do present extraordinary circumstances, and that they are never attempted except where the temptation has been made great, by the thieves seeing that they had unexpected facilities offered them. It is therefore 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. The process need not be continuous. A good hand will do part of his work, and measure it, or mark it off upon his false key, one day, and more another, until it is all done, and his key ready for action at the first convenient opportunity. Recent experience has shown that your own officers, clerks, and servants are the people from whom you have most to apprehend, and they are just the people who have the most time and opportunity to perform their key-making operations undisturbed. Without going into all the mechanical details (which it is perhaps as well not to publish), it is enough to say, that the lock of the United States Bank, which was almost as complicated as the famous one of Day and Newell, and contained all the false notches, revolving curtains, and other provisions which have been several times re-invented or put out as novelties here, was nevertheless picked for a wager.

We shall now describe the principal inventions that have been made within the last few years, with the view of defeating that tentative method of picking to which all our locks, as constructed before 1851, were and are liable; and we shall point out which of them really do effect that object, and may be regarded as absolutely secure against any mode of picking at present known; and which of them may be regarded as safe enough for ordinary purposes, though not coming up to the mark of absolute security.

Hobbs's Lock.—The invention which most directly meets the defect of all previous locks is Mr Hobbs's moveable stump, which, it must be observed, is a totally different thing from the great twenty-guinea American lock of Day and Newell, which also goes by his name here, because he makes and sells them. In Hobbs's lock, the stump is not rivetted into the bolt as usual, but is set on the end S of a bent lever STP (fig. 19), which lies in a hollow of the bolt behind it, turning on a pivot in the bolt itself, and kept steady by a small friction-spring, not shown in the drawing. The stump comes through a hole in the bolt large enough to let it have a little play; and the long end P of the lever stands just above the edge of a square pin, 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 enough to turn this protector lever, as Mr Hobbs calls it, on its pivot T, and so bring down its end P 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 Mr Hobbs himself for another purpose, viz., pushing a piece of watch-spring through the key-hole, and up behind the bolt, so as to reach the protector at P, and keep it up while you push the bolt back; or, again, by pushing up the watch-spring between any two of the tumblers, and holding the end S 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 key-hole happens to be large enough to admit the 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 key-hole. 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 key-hole, 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, at least in America, where they seem to be considerably ahead of us in these matters. It requires a largish key-hole, however; and it may be prevented by any kind of revolving cylinder, which will conceal the view of the tumblers while the key-hole is open. The one that does it most completely is the eccentric cylinder, which will be described in the great American lock. The inspecting Parnell's Locks.

The 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.

There is another lock invented by Mr Hobbs, also belonging (as far as we can see) to the absolutely secure class; but it will be more conveniently described after we have noticed the changeable key-locks.

Parnell's Locks.—The next contrivance for preventing the tentative mode of picking is that invented by Mr Parnell (fig. 20), and now sold by a Mr Puckridge, with whom Parnell was in partnership for some time, but has now left that firm, and set up for himself at another shop, with a later invention of his own, which we shall describe presently. His first lock acquired some celebrity from a trial at law, in which it appeared that a certain Mr Goater, who worked for Mr Chubb, had claimed 200 guineas for picking a challenge lock of Parnell's,—the fact being, that he had first clandestinely taken the cap off and made a false key, and then pretended to pick it. But the trial proved no more in favour of it than the pretended picking proved against it; for there was no proof that the lock could not be picked by other means; and we cannot think it would present much difficulty to those who can pick such locks as Jones's American bank-lock, before alluded to, though it would probably defeat the ordinary race of lock-pickers.

The most important features in this lock are, the lever E at the top, which is called a double-action latch. It is, in fact, Chubb's detector, with the addition of the tooth on the left hand, which falls into the bolt and prevents it from being pushed back against the tumblers, except when it is raised by them, or any one of them, just enough to clear the bolt, and no more; for if raised too high, it locks into the bolt at the other end, like Chubb's first detector. But it is evident that this is worth very little by itself; for you have only to put the pressure on the bolt, and then gently raise the lever by one of the tumblers until the bolt will either clear it completely, or, at any rate, press against some of the tumblers, and then proceed as usual. But then another lever is added. You observe a line across what appears to be the stump S. The part below the line is the real stump; but the part above it is a kind of second stump set on a tumbler behind the others, and not touched by the key, but pressed upwards by a weak spring, so that it can only rise when all the tumblers are lifted. This self-acting lever also ends in a square corner, which butts against the real stump when it is down; so that, if you push the bolt back, you bring the stump against the self-acting lever, and not against the tumblers. All this looks very formidable; but on examining one of these locks, it occurred to us at once, that if you only lift all the tumblers a little, so as to let the self-acting lever rise out of the way of the stump, and then (but not before) push the bolt back, you have disposed of the lever just as much as if it did not exist; and on trying it, we found the operation perfectly easy. Of course, it would require more care and delicacy to manage the "double-action latch" and the "self-acting lever" together than either of them separately; but they are only used together in the most expensive of these locks; and moreover, it is a maxim in lock-picking, that a mere multiplication of difficulties does not produce impossibility, and that no number of approximate or partial securities amount to one absolute security.

The mode of operation just now described will defeat equally well a self-acting tumbler, on the same principle, which Mr Chubb added to his locks soon after Mr Hobbs's demonstration, in 1851, of the insecurity of his and Bramah's, and, indeed, of all the then existing English locks. Mr Parnell (or Puckridge) also uses, in his large locks, a revolving curtain and cylinder, or barrel, which covers part of the key-hole, and the web of the key expands as it turns; for, when the key is out of the lock, it looks like a blank, with no bits projecting. But all these things, and the double-action latch too, are all old inventions, as may be seen in the Rudimentary Treatise, and more fully in Mr Price's large book on Fire-proof Safes, Locks, and Keys (published since this article was written), which is the most complete treatise on the subject ever published in this country; though even in that some of the descriptions are so brief as to be hardly intelligible, in consequence of the enormous number of inventions—nearly all patented, and most of them useless—which have been made for the improvement of locks within the last forty years. Besides being an old invention, an expanding key is very limited in the range or variety of the bits, expensive, and unpleasant to work on account of the increased friction. The pieces marked FF (in fig. 20) are called sentinels by the inventor, and they are intended to prevent the cylinder from turning beyond a certain point with a false key, and also to prevent the false key from getting out again. This, too, has been done before, and on the same plan, of preventing any key, whether true or false, from returning; and so, if it cannot go forward and open the lock, it is held fast, as evidence of its own intrusion, like Cassim in the cave of the Forty Thieves. But when the inventors of these things talk of the "frightful consequences" of having to smash the door in order to get the false key out, they forget that the key is not the thief, and that these consequences are rather amusing than frightful to the person who left it there, who will have the satisfaction of knowing that he has, at any rate, done as much mischief as possible, by way of paying off the owner for not providing him with a lock more easy to pick. It is also to be remembered, that if the owner himself carelessly puts a wrong key into the lock, or if there is a piece of dirt sticking to it, which may prevent it from opening the lock, the consequences are equally unpleasant. The detention apparatus clearly adds nothing to the security. If the "sentinels" really do their other duty of preventing the cylinder from turning beyond a certain point except with the true key, you want nothing more, and get nothing more, by detaining an intruding key; and if they can be held or thrown out of action (as we rather suspect they can), that, of course, would be the first thing a skilful lock-picker would do. We do not mean to say that a lock with all these complicated provisions could be picked under several hours, if at all. But it does not seem to us in the least degree more secure than Mr Hobbs' much simpler and cheaper contrivance of the moveable stump, or than some others which we have not yet described. And it is necessary to caution the public against shop-window locks in general, with large wagers set upon them; for unless you know that the lock exhibited in the window is the same as those usually sold in the shop at a moderate price, and unless the conditions of the challenge (which are generally "to be had within") are fair (we have seen some that were utterly unfair and absurd), the offer of "200 guineas to the artist who can pick this lock" does not prove that any other lock in the shop is worth 200 pence; and it is, in fact, nothing but a mere advertising trick.

Mr Parnell's other lock, sold by himself only, has the Parnell's Lock.—The advantage of being much cheaper, and at least as secure as the one with the self-acting lever and expanding key, which is the ordinary construction of the locks under his former patent. This lock has also the revolving curtain, and there is a small ring B (fig. 21) on the under side, which incloses a deep circular ward set in the back of the lock, which requires a very deep cut in the key, so that there would be very little room for a pick to play in. These two features are not claimed by Mr Parnell as novelties, and, in fact, they are old enough to be open to anybody. The curtain has another ring near its edge, which just comes over a pin P in the uppermost tumbler when it is down, and prevents it from rising, except when the curtain is turned far enough round to bring the gap at C in the ring over this pin, which happens just when the key begins to lift the tumblers. But the real peculiarity of the lock is this: In locking, just before the key leaves the tumblers, it delivers the stump, not into the place where it is now shown lying, but into the notch S; but before it leaves the lock the key encounters the end of a lever K1, which pushes the bolt back a little, and so lets the tumblers drop a little lower, with the stump in the position shown here. When the key opens the lock again, it passes by the end K of the lever, and first lifts the tumblers a little by their corners, near K, at the same time that the gap C in the curtain-ring comes over the pin P; then it encounters a piece that comes down from the bolt near T, and shoots the bolt forward a little, without which the tumblers cannot be fully raised (as will be seen from the shape of the false notches), and then the key operates as usual. Nevertheless, this certainly cannot be placed in the class of absolutely secure locks; for if a pick can be got to work over the neck-ward and curtain-ring or barrel, which is well known to be possible, it does not appear to us that there would be more difficulty in picking this lock than any other with false notches; for it makes no difference that the bolt has first to move forwards a little and then backwards, and the curtain could easily be got into the position to free the tumbler which it holds. However, these locks are sold a good deal cheaper than other locks with much less security used to be, and, if not absolutely secure, they are sufficiently so for all common purposes.

This reduction in the price of good locks, besides the improvement in the quality, is plainly the consequence of the exposure of the defects of all the existing English locks in the Great Exhibition, which some persons endeavoured to smother as dangerous, and others to explain away as proving nothing against the character of our locks. Not only have we got Mr Hobbs's own improvements in construction, and reduction in price, by the introduction of machinery for lock-making to an extent hitherto unknown, but there is now in the market a variety of what may be called very good locks, even though most of them could be picked by a very first-rate hand with plenty of time, and at lower prices than were charged for the only two locks which had any reputation until the last few years, viz., the Bramah and the Chubb locks. And the mere variety of locks is in itself a source of security, because a thief no longer knows by the look of a key-hole what kind of machinery he has got to deal with inside.

Restell's Lock.—There is only one other modification of the old many-tumbled lock that we need notice, and that is Mr Restell's. The only peculiarity in it (for the revolving curtain and barrel are much too old to be so designated) is the addition of a disc at the bottom of the barrel, in the same plane as the bolt. The bolt can only pass when the disc is in one position, i.e., when a piece which is cut out of it is just under a kind of tooth in the bolt; and at all other times the disc, lying partly within the bolt, holds it fast, and prevents any pressure being put on the tumblers. But this, again, proceeds on the erroneous but common assumption that the instrument for feeling and lifting the tumblers a little at a time cannot be used when the key-hole is closed, except at the centre, by the curtain and barrel; whereas it is, in fact, worked through a kind of hollow key, which presses on the bolt while the pick works the tumblers, and it can be done in locks with far greater impediments to it than this, although we say of this, as of Mr Parnell's, that it is an improvement upon any of the locks made before 1851.

Locks without Tumbler-springs.—We now come to a class of locks in which the tumblers or slides are no longer moved one way by springs and the other way by the key; for we shall postpone the description of the complicated American changeable key locks until we have taken the reader through the easier matters. In the locks we are now going to describe the tumblers, or slides, or discs, which stop the bolt, are kept in their places by friction only, and will stand anywhere, having thin plates lying between them, and being pushed or turned one way in locking and the other way in unlocking.

In the Exhibition of 1851 there was a disc or wheel lock exhibited by an American named Jennings, who used to expound it with great eloquence as cheaper and better than any other lock in the world. It had also a changeable key, i.e., the key was a mere stalk or shank, fitted with small rings, each with a bit projecting from it, and they could be transposed, together with the corresponding parts in the lock. This of course can be done, and had been done before, with the key of any tumbler-lock, if you take the lock off and change the tumblers, provided the bits are made to fit into the key, instead of being part of it as usual; but we shall have to say more of this hereafter. We have been unable to learn what has become of Mr Jennings or his lock, except that Mr Hobbs showed us a very simple way of picking it, by poking a piece of watch-spring, with a hook at the end, between the discs, and feeling for the notch in the circumference, and then bringing it round to the right place for the lock to open.

Andrews's Lock.—Another American lock on the disc Andrews's principle, by Dr Andrews, was exhibited at the Society of Arts in 1853, with some others that we shall notice, when that sagacious body awarded its premium to a lock made by a Mr Saxby, which Mr Hobbs forthwith picked in three minutes with a bit of wire, and then reminded them that he had himself exhibited a drawing of an old lock of the same construction at a lecture in that very place only about a year before. Dr Andrews's is called the small-wheel lock, because all the discs except the upper one have small-shaped holes in them, as in the last of these figures (fig. 22). The upper disc has only a square hole (except that for the drill-pin on which they all turn), which is the key-hole, and that disc always Andrews's travels with the key; the others only begin to move in one direction as soon as the key encounters the spiral edge of the hole, and of course they are carried to different distances, according as the corresponding bit of the key is shorter or longer. They are separated by loose thin plates, which cannot turn with them, and act as friction plates. Each disc has a notch in it, and it is only when all these notches are brought together under the end of a spring lever, called a "toggie," that it can drop into them. As soon as you feel or hear that take place, you have to turn the key back again, and the discs still keep together, because the toggle fills up all the notches, until it is worked out, as they revolve, and it carries the bolt with it; and then the discs no longer move together, but some lag behind until the key reaches the square end of all the snail-holes, and so brings them all into the original position, with the notches standing in different places, and then the key can come out. We do not know by what method this lock can be picked, as it can hardly be possible to distinguish between the pressure of the toggle on the edges of the discs and the absence of pressure when it is over a notch, on account of the great amount of constant friction; and the smallness and eccentricity of the key-hole would make the watch-spring method extremely difficult, if not impracticable. But besides the key-hole being thick and clumsy, on account of the great friction which it has to overcome, the lock is uncomfortable to work, and it is therefore not likely to come into use against the easier locks with smaller keys, and equal, or at any rate sufficient security, which are now made.

Tucker's Locks.—There have been several locks on the disc principle invented in succession by Mr Tucker, of Fleet Street, the first two of which had revolving discs; and in the last and more simple one, patented in 1855, though the discs no longer revolve, they slide between fixed plates without springs, and do not turn on a pin like common tumblers, and will stand indifferently 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. 23, TT is one of the sliding tumblers, 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 J, 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 described. This curtain also 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 movement in the key-hole would be prevented by the barrel Tucker's 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. The only way (so far as we can see) to prevent this is by a contrivance, such as Mr Denison's lock (described below) was first made with, of a kind of door between the tumblers and the key-hole, which opens for the key just before it reaches them, and closes again after it has moved the tumblers, and before any action at all upon the bolt begins. It will be seen hereafter that in that lock this shutting off the tumblers from the key-hole was afterwards carried still further, as the key there does not operate on the bolt at all, but must be thrown out of the key-hole, and the hole completely closed, before the bolt can be drawn back; but the first arrangement may very well be used in cases where the key is wanted to operate 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 key-hole. 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 tumbler-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 key-hole, 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 farther; 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 just now 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. This drawing of it (fig. 24) 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 screw-driver above the lock, and forcing up the piece over it just enough to let the bolt pass, which is generally short. 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.

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, some 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-tumbled locks, some with the tumblers acting upwards at one end and downwards at the other (Parson's lock); and others with some of the tumblers pulled down by bits cut within the web of the key, besides the usual ones to be pushed up by the key (Somerset's); and some with a combination of the Bramah plan in the pipe of the key, with the Chubb plan in the bits, and so on; but none of them involve any novelty in principle, and they are all capable of being dealt with in the same way: and therefore 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 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 farther by the key, and having 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 (which is the most they are ever locked in 99 cases out of 100), 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 key-hole. 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-door handle.

There are two ways in which spring-locks with tumblers may be 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. 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-locks, not to let the key act directly on the bolt, which has no stump, but on a 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 key-hole. 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 the peculiar construction to be described immediately.

Chubb's Latch-Lock.—In order to prevent the bolt from being pushed back by a piece of wire poked in between the latch-lock door and the staple into which it locks, Mr Chubb has made the following ingenious modification of the common latch-lock. In fig. 25 the bolt is drawn back by turning a handle H as usual, but the handle also raises all the tumblers like a key. But the back tumbler T is not set on a fixed pin as usual, but on a pin in the bolt, and so travels with it; and when it is drawn back far enough, i.e., about half way, the spring S falls in front of that tumbler at T, and so, when you leave hold of the handle again the bolt only goes about half way out, as far as B, the point to which its face is belvelled. But when you push the door to, the sloped corner of the bolt at R raises the spring S, and the tumbler T not being then held up by the handle, it falls and clears the spring, and so the bolt shoots the whole way out, and the other tumblers fall upon its stump, and it can only be To prevent confusion, we may observe that there is another lock called Chubb's latch, in which the bolt consists of a number of tumblers prolonged. But this is a very inferior article to the latch-lock just now described, or even to a latch-lock made in the second of the methods above mentioned. We understand the latch-lock is used extensively in prisons (of course without the handle), where it is not only desirable to avoid the necessity of having to lock the cell doors by a key, but also to provide against the ingenuity of the inmates in pushing back the bolt of a spring-lock. It has been suggested however, that this provision may be defeated by a prisoner, or any other thief not yet in prison, putting something into the bolt-hole which will prevent the bolt from shooting full out, and then the tumblers will not fall, and the bolt can be pushed back easily. A safer lock for this purpose is one which we shall describe presently, and which locks by merely turning the handle, but cannot be opened without the key.

We may observe also with reference to these latch-locks for house doors, that they very soon get spoiled, at least so far as to impede their action, and render them unsafe, by the dirty atmosphere of a large town. This might easily be prevented by using a spring curtain like that which we shall describe in Mr Denison's smaller lock. If purchasers of locks would insist on having such an addition made, it could be done without increasing the cost by more than a shilling, and it would save its price many times over, by the length of time the lock would go without cleaning, and last without being spoilt. But unless purchasers insist upon having it, it is not likely that the lockmakers will volunteer such an improvement. The curtain should slide easily on the drill-pin and on another pin, just below the lower end of the key-hole, and be pressed up by a long thin spring acting upon it near the drill-pin. We suggested this some time ago to a celebrated London lockmaker, and he undertook to get it done. After some months he produced a lock, with a spring curtain certainly, but (with that peculiar ingenuity for baffling any new invention which English mechanics generally display) the curtain made to slide on two pins set at some distance on each side of the drill-pin, instead of a single pin below it; and the consequence of course was, that there being nothing like the web of the key to push the curtain down straight, it went rather obliquely, and generally jammed itself fast upon the pins, and then (as usual in such cases) was pronounced impracticable, and thrown aside; and all this with one of Mr Denison's small locks as a model to copy, in which the curtain slides up and down quite easily. It has since been done properly by Mr Hobbs; and there is plenty of room to add it to any existing lock which has a false bolt lying above the true bolt for the key to act on, as every good latch-lock must have; for otherwise the tumblers are of no value whatever, as explained above.

Safe Locks with Small Keys.—In all the locks we have yet mentioned, the bolt is acted on by the key, even though the key may not touch it; and 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 impregnable of the small lock against fraudulent picking or forcible evisceration. And it may be mentioned here that there are certain thieves' instruments, by which a force sufficient to tear open the inside of a lock can be inserted through a key-hole 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-the-box, or from 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.

Denison's Lock.—A lock was invented however, in 1852, but not patented, which combines the advantages of large lock and strong works, with a key-hole 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 shut by turning the handle, but locked besides, without using any key at all. But it cannot be opened without the key; consequently, there is no occasion to entrust the keys to clerks, or other persons who may be left to close the boxes or doors, provided the owner, or some one confidential person, is there in the morning to open them. This lock enjoys the distinction of being the only one of English invention which is pronounced secure—at least against any known method of picking,—by Messrs Hobbs and Tomlinson, in the treatise before referred to. It was invented by Mr E. B. Denison, Q.C., whose name has been frequently mentioned already in the article on Clocks; and the following is its construction:

In fig. 26 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 tumbler-pin, 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 gating, and the bolt can be drawn back by the handle, the tail Y then doing nothing. So far as we have gone yet, the lock would possess no greater security than any other many-tumbleder 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 key-hole 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. 27), 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; so that 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. 26), in order to keep the bolt steady. It is evident then, that as soon as you push in the curtain 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 of 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 further increased by the addition of what may be called a detector DEG, 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 jumper-spring at E, as in Chubb's first detector. In fig. 26 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; and 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 make 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 shot, so that no exploration of the lock can take place while it is open, or even partially open. 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, by adding a spring catch under the curtain, to be freed by one of the tumblers when it is fully locked.

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, a large spring-lock requires a large and strong key to open it. 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 key-hole 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 key-hole 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 them together are fewer than the number of springs alone in the great American lock which we shall next describe. 8. It is free from the incumbrance of a patent, the inventor being one of those who agree with the opinion of the Jury on Philosophical Instruments in the Great Exhibition, 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.

Notwithstanding these advantages, we cannot learn that any of the lockmakers have taken up the manufacture of this lock, all of them having a settled course of manufacture of their own articles, which they find they can sell sufficiently; and unless some large order should be given for this lock (as for a set of prison doors, for which it seems peculiarly adapted, with a master-key arrangement) it seems not likely to be adopted until some startling event makes the public open their eyes to the insecurity of the established forms of English locks which they have long believed in.

We now proceed to describe what has been considered the great triumph of transatlantic skill, viz.:

Day and Newell's Parastoptic Lock.—This formidable Day and name has nothing to do with the chief peculiarity of this Newell's lock, viz., the power of changing the key and the state of lock without taking it off the door, which might have been indicated by an equally imposing title—parallactic. Parastoptic only means that it cannot be examined through the key-hole, which is not peculiar to this lock. In order to understand this complicated machine it will be better to consider the provisions for security against picking, and those relating to the changeability of the key, independently of each other, as they have nothing to do with each other, and either might be used without the other. The object of the changeable key is merely to provide against the risk of its falling into the hands of somebody who may have taken an impression, and made a false key from it: a risk which is perhaps rather more likely to be increased than diminished by the great size of this key, and the dis- position of people not to carry such a large instrument in their pockets more than they can help, and the probability of their not taking the trouble to unscrew the bits and change the form of the key every time they use it. Assuming then, for the present, the key not to be made with moveable bits, the security of the lock depends on the following points:—The stump ss, which for the present must be assumed to be attached to the bolt, does not act against the tumblers TT, which are raised by the key, and may be called the primary tumblers, but on a set of secondary ones tt, which are made to follow the primaries whenever they are raised by a set of springs under them, which are not strong enough to resist the primary tumbler-springs, but are strong enough to lift the secondaries when the pressure of the others is taken off. But even this does not fully represent the independence of the secondary tumblers, for each secondary tumbler tt really consists of two pieces, of which one is pushed up by the spring and lifts the other with it, which has the gating or jaws to receive the stump, but can rise without the carrying piece being lifted. The consequence is, that supposing pressure to be applied to the bolt so as to hold fast one (or more) of the secondary tumblers, it only holds the gating piece, and the corresponding primary tumbler remains as free to move up and down as if there were no pressure, and therefore the pressure cannot be felt. Moreover, there is a fixed wall in the lock between the key-hole and the secondary tumblers, so that it is impossible to reach them from the key-hole. All the tumblers move between parallel guides, instead of turning on pins as usual; and the primary ones are also separated by thin loose strips of iron, which prevent them from sticking together. The secondaries, however, would be the most likely to stick, as their springs are weaker; and as their action depends entirely on the springs, which are comparatively weak, we cannot help thinking there is some risk of their getting stuck together by rust forming between them, or by a drop of thickened oil, as sometimes happens in Chubb's, or any other spring tumbler-lock.

The primary tumblers are also prevented from being inspected through the key-hole by a curtain cc, which is not the ordinary flat curtain with a small barrel close to the key-pipe, but a large ring or barrel turning in a circular groove in both the lock-plates. Moreover, this curtain is not concentric with the key-hole; and therefore, although the bits of the key do not project beyond the curtain when it is put into the key-hole, yet by the time it has got nearly half round they project considerably, and raise the tumblers as if there were no curtain at all in the way. On the front edge of the curtain there is a broadish flange with a segment cut off at the top, and on that segment there lies another tumbler (covering the primary tumblers, and supposed to

In this figure, which is copied from Mr Hobbs's Rudimentary Treatise on Locks, the detector plate is drawn the reverse way of the two figures of the lock; for what reason we are not aware. the key would require making shorter or longer in order to raise the tumblers to the proper height. Suppose next that each tumbler had a stump of its own screwed to the bolt, but capable of being unscrewed and shifted at pleasure, then every hit of the key would require altering whenever you alter the position of the corresponding stump. And again, suppose these separate stumps to be so attached to the bolt, by a ratchet and click, or some similar contrivance, that when the bolt is back and the stumps lying in the jaws of the tumblers, the tumblers will carry the stumps with them to whatever height they may be raised by a key, and leave them sticking to the bolt at that height when the bolt is shot, and the stumps pass out of the jaws of the tumblers,—then it is clear that the lock can only be opened by the same key which raised the tumblers and stumps to that particular height; and yet, as soon as it is opened, the stumps again come under the dominion of the tumblers, and any other key will do to lock the lock again just as well as the one which was used before. In other words, such a lock is perfectly neutral and indifferent as to the key which may be used to lock it, but it cannot be unlocked by any key except the one which locked it last; and, therefore, by changing the key, or the arrangement of a given set of bits fixed to one stem, you change the lock also.

We may observe, that a key with transposable bits is by no means new; but then it always before required the lock to be taken off, or the tumblers transposed by some other operation, to suit the alteration of the key. Fig. 32 shows the construction of any changeable key, the bits being put in in any order, and fastened by a screw going through them all.

Now, to apply this to Newell's lock. In fig. 28 it is shown unlocked, and the moveable stumps ss are then lying within the jaws of the secondary tumblers tt; and besides that, they are now taken hold of near the top by the long pieces projecting from the primary tumblers TT. Consequently, when the primaries are raised by the key for locking, the sliding stumps ss are lifted with them; and as they slide up and down between guides fixed to the bolt, they are carried forwards, and out of connexion with the primary tumblers when the bolt is shot; but just before the connexion ceases, a click & falls into the back of the stumps (which are notched for the purpose), and holds them at the same height until they return. There are as many notches in the stumps as there are different lengths in the key-bits; and, as before stated, there may be any number of bits capable of fitting on to the same key, whether of the same or different lengths, so as to increase the variations in the lock without increasing the number of the tumblers.

These locks do not appear to have been as yet much adopted in England; whether from the cost, the ponderousness of the key, and the trouble involved in taking it to pieces frequently (for without that, the changeability is no security whatever), or merely from the national antipathy to novelties, and the national confidence in our own security, we do not pretend to say. It is certain that, in America, both the thieves are more dexterous, and the owners of property spend much more upon locks and safes than we do. A New York watchmaker told us lately that he locks up all his valuable goods every night in a cast and wrought iron safe two inches thick, with a lock that cost L50. There are however some of them used in the Bank of England, and a few other banks.

The French Changeable-key Lock, though very inferior to the American ones in security, has this advantage, that nobody can lock or change it for mischievous or fraudulent purposes without possession of the key that last locked it. The primary tumblers which are raised by the key do not contain the gatings for the stumps, but work a second set of tumblers which do, by means of teeth, like two toothed wheels working together. In order to change the lock, you overlook it backwards a little with the key that will open it (i.e., which locked it last), and, by turning a small handle, you throw the two sets of tumblers out of gear with each other. Then change the bits of the key as you please, and put it into the lock again and turn it, as before, half-way round, and bring the tumblers together again by the handle. They will join by a different set of teeth from before, and the altered key alone will open the lock. This plan may be adapted to any kind of tumbler-lock; and if it is one of a secure construction, it would be just as good as the more complicated American lock. Mr Chubb has lately made some of these locks; but in this instance also, the necessary size and weight of the key seems to be an impediment to their use; and probably any one who was inclined to spend a largish sum on a changeable lock, would buy the American one, which is undoubtedly very superior to the French in security both against picking and violence.

In order to get over this disadvantage of a large key, Mr Hobbs invented another lock, which is equally changeable, and still more parapoptic or secure from inspection, than Newell's. The key that you have to carry is, in fact, nothing but the web or bits of a key, which may be either fixed or changeable, according to the nature of the lock. The key-hole has no centre of motion within it; but when this web of key is pushed into a hole in the lock, you turn a handle in another place, and that carries the key round quite invisibly, closing the hole completely; and as it turns, it opens the lock in the usual way, and returns. There is no possibility of feeling or examining its action, as no handle can go with it into the lock. The only objection to it is, that it is troublesome to put such a key in, and still more so to get it out again; and consequently, it has not taken with the public, nor do we believe that any lock will, which does not admit of a moderate-sized key of the usual form, and to be used with no more trouble than usual. We cannot help thinking that some spring action might be contrived, which would enable this very neat and small key to be pushed into the lock and shot out again, with no more trouble than is involved in turning a key and then a handle, as in the now common arrangement for large safe locks.

In fact, after we had written this, Mr Hobbs sent us a Yale's lock, new American lock, invented by Mr Linus Yale of Philadelphia, in which this very thing is done; the bits of the key being taken off the shank or handle, and carried away into the inside of the lock, where they perform their work, and rejoin the key shank before the revolution is completed. But the key itself is so large and thick, that it is far from realizing the advantages just now suggested in Mr Hobbs' travelling key-bits. The description sent with it is unfortunately quite unintelligible without an inspection of the lock itself, and the lock is so complicated, that we despair of being able to convey any idea of more than the general principles of its construction. It is a changeable lock, like Newell's, and with this great point of superiority over that lock, that it is entirely independent of the action of tumbler-springs; the moveable stumps, and the sliders or tumblers which act upon them, all lying between friction plates, as in Denison's and Tucker's locks, and standing indifferently anywhere. The only spring is a long spiral spring in the shank of the key (fig. 33), which drives a pin through the bits (which are all screwed together just in whatever order you please), and that pin yields to another pin in the lock, which meets it as you push the key in; so that the bits then become attached to this lock pin, which itself moves on a sliding stud, which carries off the bits into the acting part of the lock against the ends of fig. 32. the sliding tumblers. This part of the lock, viz., the box containing the sliders, is shown in fig. 34. Any of the primary sliders T, when pushed by the key, carries along with it the corresponding stump-slider S, and these sliders correspond to what we called the stump-tumblers in Newell's lock. After that is done, the box BB, which contains those sliders, is moved upwards, and delivers them all to the tooth Q, which holds them in whichever of their notches it happens to receive them. The primary sliders having been brought back by other motions in the lock to their original or neutral position, the box BB cannot be brought down again until all the primary sliders are pushed by the proper key into exactly the same position as they were when they parted with the stump-sliders. This part of the lock is really very simple, and involves no delicate or difficult work, as all the tumblers, all the stump-sliders, and all the little plates which lie between them both are, or ought to be, exactly alike, and may be stamped out of sheet-iron and brass; and the whole thing goes into a very small compass, although the lock itself is very large. We may observe here, that if you were to take the key out of the lock (filing off the small bit like that in the Bramah key, which goes under the cap to keep it in), after the bits are cut off and carried away into the lock, you would not find the key-hole open, but closed at the depth which takes in the bits by a hard steel plate, which slides over it as soon as the box or "carriage" of the tumblers begins to move.

It would be natural to suppose that the cross piece BB at the end of the slider-box is the bolt, as it is prevented from moving down as a bolt usually is, until the stumps can enter the jaws of the tumblers; and this cross piece is, in fact, lifted by a kind of talon turned by the key, just like an ordinary bolt. But, nevertheless, it is not the bolt, but merely locks into the bolt, or rather fits a lever which does, so that no amount of force which could be brought to bear on the bolt has any tendency to crush the tumblers or sliders; and this is the reason why they can be so small while the lock is very large. The key however cannot be said to be small, for it is even thicker than Newell's; but you might carry only the bits in your pocket, and stick them on to the handle or shank of the key, which may be left anywhere near the lock. Another singular provision is introduced in this lock. The bolt or bolts are not square-cornered as usual, but large round cylinders, case-hardened, so that if you attempt to cut them with a saw they will only roll under it. Figure 35, which is copied from a paper called the Scientific American, shows the general aspect of the Yale's Lock when the front plate is taken off. All that box marked bb, which is as large as an ordinary lock, moves to the left, and carries the bolts with it when the lock is locked, leaving, of course, some of its parts behind under the key-hole. The piece here marked ii is that which we called BB in fig. 34, and it works the lever b, which butts against the horizontal piece lying under the tooth-wheel f, when the lock-carriage is shut out. It will be understood perhaps by those who are conversant with machinery, how the different parts of this carriage, and the plates which cover it, may be carried backwards and forwards by the toothed wheels and pins shown in this figure; but, as we are convinced that any attempt to explain the details of this machinery, without having the lock itself before you, would be useless, we shall content ourselves with the attempt we have made to give some idea of the general principles of its action. We will only add, that the casting of both these American locks (which have all their heavy parts of cast-iron) is vastly superior to any iron casting we have ever seen made in England; and, on the whole, the United States are evidently far ahead of us in the manufacture of both good and cheap locks; and all because our people are too stupid to substitute machinery for hand-work, and because (as Mr Hobbs said in the discussion at the Society of Arts, on the establishment lately set up by the government for the manufacture of arms at Woolwich), "if the English workmen can do anything to make a machine go wrong, they will; whereas in America they will do all they can to help it." In the same way the American and French manufacturers of clocks have driven our makers both of common clocks and of ornamental clocks out of our own market; and any enterprising manufacturer might very soon finish the business by making both church and house clocks at half the price which is paid for the old-fashioned hand-work of Clerkenwell, and of far better quality.