The springs of the levers are formed out of the solid metal of the levers themselves, and are thus not liable to that displacement which so often occurs with separate springs, nor to the corrosion by oxidation incidental to steel springs. They are cut round the corner, and down the front of the lever, to gain greater elasticity.
In [fig. 65] the lock is shown with the front plate removed, and the works as they stand when unlocked. [Fig. 66] is the same, except that the works are shown locked, and the back plate removed instead of the front. [Fig. 67] shows the front view of [fig. 66]. [Fig. 68] shows the result of any attempt to pick the lock by pressure.
fig. 66.
fig. 67.
fig. 68.
The lock being locked, as shown in figs. 66 and 67, it will be seen that the stop a just clears the angle d of the bolt-head. Further, that the gatings r of the levers l cannot pass the stump s, unless the levers be so lifted as to coincide with each other and the stump. The stop a being held up by a very light pressure from the lever springs, a small force applied to the stump s is sufficient to upset its equilibrium, and bring down its end a2 upon the bolt-head at d, as shown in [fig. 68]. This occurs whenever an attempt is made to “feel” the stump with the levers; and not only does the stop a free the levers from all pressure, and so preserve them and the stump from injury, and the lock from being picked, but it also forms a strut for securing the bolt: in fact, no violence short of that necessary to shear the pin b can make the bolt yield.
The drawings show a mortise lock, but the improvements shown are universally applicable in the construction of locks of all kinds.