HOW IT WORKS.

combinations possible is still enormous (several millions). In our illustrations (Figs. 219, 220, 221) we show the mechanism controlling the turning of the key. The keyhole is a narrow twisted slot in the face of a cylinder, G (Fig. 219), which revolves inside a larger fixed cylinder, F. As the key is pushed in, the notches in its upper edge raise up the pins A 1 , B 1 , C 1 , D 1 , E 1 , until their tops exactly reach the surface of G, which can now be revolved by