Page:A Dissertation on the Construction of Locks (1815).pdf/41

 all admit of pressure beyond the point which brings these notches parallel with the plate. The necessity of the proper key to the purpose of opening this Lock, and the certainty that it cannot be accomplished by other means, will be clearly seen from the process which puts it in motion. By a distinct and unequal pressure on the sliders, the notches must be formed into a groove, in a line with the plate, n, n, which those notches are exactly fitted to receive. The least motion of the barrel while the sliders are in this position, will introduce the edge of the plate into the groove thus formed by the notches, and controlingcontrolling [sic] the power of the spring, permit the barrel to move round and protrude the bolt. The impossibility of thus bringing the notches on the sliders to fall into a direct line, and to form a groove which shall perfectly tally with the inner edge of the plate, n, n, by any other means than the application and impulse of the key, is the principle of security which constitutes the peculiar excellence of this Lock. The key is represented at Fig. 5, and its indented point or extremity corresponding with the depths of the notches is seen at Fig. 6. It will be recollected, that the upper ends of the sliders overhang, or project into the