WARDED LOCKS. The origin of warded locks is 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 tee the beginning of the last century, (Well 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 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 earl be used. The bolt has at the end opposite to that which enters the staple a small piece slit, bent outward. and tempered hard; this forms the spring: below are two notches, divided by a curved 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 tumbler lock is an advance upon the lock just described. In its simplest form the holt has neither the stringpieee nor the notches and curves on the under side, but it has two notches on the upper side, which are exactly as far apart as theistance moved by the bolt in locking or unlocking. Behind the bolt is the tumbler. a small plate moving on a pivot. and leaving pro jecting from its face a small square pin, which when the bolt is locked or unlocked falls ex actly into one or the other of the small notches. There is in the key a notch which corresponds 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 its 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 suffi 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 medixval times, the keys are pipe shaped, to slide onto a fixed pin in the lock, like the old-fashioned watch-key. Such leeks are now used chiefly in cabinet-work. Chubb's lock
(originally patented in NIS) carries out the tumbler principle most fully, the bolt itself being only a series of tumblers, with a notch on the key for each. 13ratnah'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.
The `parantoptie (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 1850. and was considered absolutely safe. It was picked, how ever, by Linus Yale, Jr.. the inventor of the cele brated Yale lock. The Yak lock, with its char acteristic flat key. was invented about and is a development of the old Egyptian The lock consists of a barrel. which turns in a cylinder in order to move the bolt. The barrel is prevented from being turned by five divided pin tumblers, which move up and down in little cylindrical rooms and pass through the lower part of the ease and through the bolt. so their lower edges come in contact with the key as it is inserted. The upper part of each pin is forced down by a little spiral spring. which is placed above it in the pin-room. This in turn presses down the lower part of the pin. so that, when the key is not in the lock, the pins hold the bolt. The pins are unequally divided, and the upper surface of the key is so shaped as to raise the pins corre,pondingly. as the division between each upper and lower pin is on the line between the barrel and cylinder. When the key is in serted the pins are gradually raised until all those iu the cylinder are raised exactly to the line bet Wee]) the barrel and the cylinder. while the lower portions of the pins are raised to the same point. permitting the barrel to be easily turned. so as to throw the bolt. Should a false key be inserted the steps on its upper surface would not correspond to the division of the pins, but some would be raised too high, projecting from the barrel into the cylinder. and some would not be raised high enough. and thus the la It would remain locked. Ilecent improvement: in the form of the key render the lock still more secure. These consist of a peculiar form of cross-section, both of the key and its keyway. whereby these parts are interlocked throughout their length and access to the tumblers made so difficult as to render the lock practically 'un piekable.' Perhaps the most familiar form of Yale lock is the latch-lock. Like all latch-locks, this one works automatically when the door is closed. It opens on the inside with a handle. and on the outside with a key. The latch is an entirely modern addition to the door-lock, which enables it to he locked or opened from the inside without a key.