Page:A Dissertation on the Construction of Locks (1815).pdf/48

 479,001,600 changes. These being again multiplied by the number of changes which the projected surface of the levers will admit, in the disposition of the notches, their amount will exceed numeration, and may therefore be properly said to be infinite. The slightest inspection of these Locks will at once evince that I do not over-rate the effect of their property of motion, in asserting that it precludes all possible means of obtaining an impression of their interior parts, which is necessary to the fabrication of a false key; for it will be clearly seen that the positions into which the sliders are necessarily forced by the pressure of the key in the operation of opening the Lock can no more be ascertained when the key is withdrawn, than a seal be copied from its impression on a fluid, or the course of a ship be discovered by tracing it on the surface of the waves. But inviolable security is not the only excellence they possess; the simplicity of their principle gives them likewise a great advantage over Locks that are more complicated, in point of duration; for their essential parts being subject to no friction, nor exposed to any possible accident from without, they will be less affected by use, and less liable to stand in need of repair.