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On the Construction of Locks and Keys by John Chubb
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26 CONSTRUCTION OF LOCKS AND KEYS.
made, with the bottoms of its several notches formed by as many small steel sliders, extending beyond the handle of the key, so as to receive pressure from the fingers, for moving each one of the sliders •within the lock, with a sliding motion in its own groove, independently of the others ; and during such sliding motion, a gentle force could be exerted, tending to turn the barrel round. Under such circumstances, supposing that the motion of the barrel was prevented by any one slider only, that one having to resist all the turning force, would be felt to slide more stiffly endways in its groove, and therefore it could be felt when its unlocking notch arrived opposite the steel plate, and left some other slider to begin to resist the turning force; such a circumstance presumed a palpable inaccuracy in the radiating correspondence between the notches in the steel plate, and the grooves for the sliders in the barrel, which could not happen with Bramah's workmanship.
It might be concluded, that a good Bramah's lock was not easily picked, by finding out its combination; but unfortunately if a Bramah's key fell into dishonest hands, even for a very short time, an impression could be easily taken, and a false key as easily made. A turkey quill notched into the form of a key, had sufficed to open a Bramah's lock; and an efficient false key could be formed out of a pocket pencil-case. Such facility of fabrication was an invitation to dishonesty, and as an abortive attempt left no trace, the impunity was an encouragement to repeat the attempt until success was attained.
A similarity of principle might be observed in Bramah's sliders, and the pins of the ancient Egyptian lock, the motions of the sliders, in the former case, and of the pins, in the latter, being in both independent, whereby any one out of the whole number would of itself secure the lock, which could not be opened until all the sliders, or pins, were brought to their unlocking position. Bramah's sliders required, however, great precision in the extent of this motion, and had also the advantage, that any one which was moved beyond its exact locking position, would interlock anew as effectually as if it had not been moved far enough.
In Barren's lock, a vast improvement was made by rendering the tumblers double-acting, and by combining two such tumblers. A common tumbler would only catch and detain the bolt, when the tumbler was let down, but it ceased to afford any security, if it was lifted beyond its contact with the bolt; hence an ordinary tumbler lock, with only one common tumbler, might have that tumbler lifted, and kept up, by a picklock, so as to leave the bolt quite at liberty, to be moved by another picklock.
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On the Construction of Locks and Keys by John Chubb