Page:A Dissertation on the Construction of Locks (1815).pdf/43

 will prove an insurmountable impediment to their motion, I may safely assert, that it is not in art to produce a key, or instrument, by which a Lock, constructed on this principle, can be opened.

Fig. 7, is a plan of a complete Lock, with a part of the cap or covering removed, to shew the original mode of applying this principle of security. The dotted lines on the bolt are the spring and tumbler, situated beneath, and having the same office as in the common Lock. The lever x, which is firmly attached to the barrel, represents the web or bit of an ordinary key, and which being carried round with the barrel, takes hold of the bolt in the notch, which it releases by lifting up the tumbler, and projects or withdraws in its revolution. But as circumstances might, by possibility occur, where ingenuity could gain access to the tumbler and release the bolt without attempting the principle of security, Locks are now fabricated in the manner shewn at Figs. 3 and 8, a method which can only be accomplished on this principle, and which vies in importance with the original invention.

Fig. 8, is a plan of the bolt, of the Lock Fig. 3. The point u, is a pin fixed in the bottom of the barrel, e, e, and which, when the barrel is