LOCK. 374 LOCK. uncertain. They must have been widely used, for they are luuud in abuiul;iui'e ia dill'eient parts of Kurope, especially Frame and tJerniany. The fourth type was used in the Roman pad- looks, and is still used in China. The bolt is kept out by the projection of a sprinji or springs which spread out apiinst the sides of the staplr. The spring's are merely flexible barba attached to the bolt, and the key is a ilattish one with prongs at the end to engage the springs. The key is passed through a liule in the door and turned and pulled. This compresses the springs so the bolt can be pushed back l)y the key. In the fully developed li.vod lock of the Romans the parts are of metal : the bolt is much shortened and is concealed behind an ornamental plate. The pins which hold the bolt vary in shape and are pres.sed down by a flat spring. The key, which reaches the bolt through a hole in the front plate, has projections or teeth in it cor- responding to the pins. The key presses up the pins and frees the bolt, so that it can slide ex- actly as in the Egyptian lock. During the Middle Ages very complicated and ingenious locks of various kinds were made, and much artistic taste was expended upon their ornamentation. Such kicks, however, were not ada|>ted to general use, and they were found only on the caskets of the wealthy. W.VBDED Locks. The origin of warded locks ia unknown, but is undoubtedly of early date, for they seem to have been used by the Etruscans. A century ago they were considered very safe, and were made in most complicated and inge- nious forms. It was the only lock generally em- ployed up to the beginning of the last century, even for important purposes, and this kind of lock is still in very common use. It consists of a bolt of metal, to which a spring is attached. The neither the stringpiece nor the notches and curves on the under side, but it has two notches on the upper side, which are exactly as far apart E.iRI.Y FOItM OF WAIIDS FROM WARD LOCK. bolt is moved backward or forward by means of a key, which by raising the bolt compresses the spring in the slot, through which it works, and so lets it pass on until out of the range of the key's action. As the key turns on a pivot, its action is regulated by the length of the wards and the depth of a curve cut in the under side of the bolt. In order to prevent any key of the same size opening all such locks, little ridges of iron are placed in circles or parts of circles, and grooves are cut in the keys so as to correspond with them: hence, only the key which has open-' ings or wards which will allow the ridges to pass through them can be used. The bolt has at the end opposite to that which enters the stajile a small piece slit, bent outward, and tempered hard; this forms the spring; below- are two notches, divided by a euned piece of the bolt; there is another notch, which, if the key enters and is turned round it, draws the bolt forward or backward in locking or unlocking, and the spring makes the end of the bolt either drop into one of the notches or rise up the curve, according to the distance to which it is pulled. The tumhler loch is an advance upon the lock just described. In its simplest form the bolt has VClyC.V.N TCUULEB LOCK. (1) Bolt in place, tumbler removed, ami shown below- (2) Tumbler in place with key belut^ turned tu liit it. as the 3istance moved by the bolt in locking' or unlocking. Behind the bolt is the tumbler, a small plate moving on a pivot, and having pro- jecting from its face a small square pin, which when the bolt is locked or unlocked falls e.^c- actly into one or the other of the small notches. There is in the key a notch which corresponda to the outline of the tumbler. This acts upon the tumbler when the key is turned, and raises it so as to lift the pin out of the notch in the bolt, and allow the latter to be moved freely forward until the other notch comes under the pin, when the latter falls into and immediately stops ita farther progress, and the action of the key must be reversed in order to relieve it again,. This very simple application of the tumbler is sulli- cient to explain the principle, which may be and is varied to an almost endless extent. Its re- semblance to its prototype, the Egyptian lock, with pins dropping into holes in a bolt and raised by a key, is apparent. In another class of locks, first used in medioeval times, the keys are pipe- shaped, to slide onto a lixed pin in the lock, like the old-fashioned watch-key. Such locks are now used ehiclly in cabinet-work. Chubb's lock (originally patented in 1818) carries out the tumbler principle most fully, the bolt itself beinj only a series of tumblers, with a notch on the key for each. Braniah's lock, patented in 1788, is very different in principle from those men- tioned, consisting of a number of movable slides or interior bolts working in an internal cylinder of the lock, and regulated by the pressure up- ward or downward of the key acting on a spiral spring. For ordinary purposes it is very secure.. BRAMAH LOCK. The 'parantoptic' (inspection-defying) lock of Day & Newell, often called the Hobb's lock, on account of the success of that gentleman in intro- ducing it, is an ingenious and complicated piece of mechanism which was widely used for some time after its introduction about IS.iO. and was considered absolutely safe. It was picked, how-
