Page:A Dissertation on the Construction of Locks (1815).pdf/42

 cylindrical cavity which forms the key-hole; when the key therefore, is applied, it must of course encounter these interior projections, and its extremity being notched in exact proportion to the several distances to which the sliders are to be carried, it will, when pressed forward, force the sliders to unequal distances from their bearings, and bring the notches on their exterior projections in a direct line with each other, and parallel with the plate; leaving the barrel at liberty to be carried round by the bit or lever on the key, (see s, Fig. 5,) and which fits for that purpose into the notch on the prominence of the barrel, as explained in the description of Fig. 2, serving at the same time to stop the key at its proper point of pressure. When the key is withdrawn, the sliders of course resume their station by the re-action of the spring, and the barrel returns to its confinement.

It hence appears, that unless the various heights of the surfaces expressed on the point of the key, are exactly proportioned to the several distances to which the sliders must be carried to bring their notches into a direct line with each other, they must remain immoveable; and, as one stroke of a file is sufficient to cause such disproportion as