INTERIOR OF A WARDED LOCK.

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that no key can be turned round within it unlesscorresponding notches or slits are cut in its pro-jecting bit. Fig. 84 , which represents a portionof the interior of a lock in isometrical projectionwith the bit end of the key in its place, willillustrate this. The tinted surface in this cutrepresents part of the back-plate of a lock with atubular key turning upon a central pin in the plate.

Fig. 84.—Key Bit and Wards.

Attached to this plate are two concentric prominentrings, of different degrees of elevation, one of whichfor the sake of variety is represented as completeor unbroken, while the other is cut away for asmall space at the under side. It is obvious thatno key could be put into a lock provided withwards as in the cut, unless a slit or notch weremade in its bit to correspond with the larger andmore prominent of the two rings—the round ward—■and it is equally evident that, although it might beput into the lock, no key could be turned round