LOCK 747 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, together 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/ 1 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 enough 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 , 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 sturnp 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 the inspecting method, which is this. A person in tending 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 may 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 185D, though the disks no longer revolve, they slide between fix ed plates without springs, and do not turn on a pin like common tumblers, and will stand in differently any where. It will be sufficient to describe the last of these Fig. 18. inven tions, as Mr Tucker himself states it to possess all the ele ments 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
