Page:A Dissertation on the Construction of Locks (1815).pdf/38

 at equal distances from the frame K. In order therefore to give motion to the bolt, a complete tally or key H must be provided, with six unequal prominent surfaces, agreeing respectively with the distances of each notch from the bolt, and by the application of which the sliders may receive the motion necessary to bring the notches in a line and form a groove for the passage of the bolt. It will be evident, that in the absence of such a key or tally, no certain information can be gained by an inspection of the projected parts of the sliders; and, as they may be severally pressed farther than requisite, as well as not far enough, every attempt towards their due adjustment must entirely depend on chance, which by demonstration is found to offer such improbability of success as amounts to a most satisfactory security, and must deter any person, acquainted with the principle, from making a trial.

I shall now proceed to describe the application of this principle, in which it will be seen, that a method is provided of restoring the sliders to an even surface after the key is withdrawn.

Fig. 2, represents the face of a circular block or barrel of brass, having a cylindrical cavity throughout, and divided from the center into eight