Page:A Dissertation on the Construction of Locks (1785).pdf/38

 inſtruments. The office, therefore, which in other Locks is performed by the extreme point of the key, is here aſſigned to a lever, which cannot approach the bolt till every part of the Lock hath undergone a change of poſition. The neceſſity of this change to the purpoſes of the Lock, and the utter impoſſibility to effect it, otherwiſe than with the proper key, are the points to be aſcertained, by a ſpecification of the component parts of the movement, and an explanation of their reſpective offices.

Among the various methods of applying the principle of motion, in the conſtruction of Locks, which have yet occurred in my practice, I think thoſe, deſcribed in the ſubjoined plates, are to be preferred, for their ſimplicity.

The firſt plate ſhows the interior face of a Lock, which was conſtructed, at a very early period of my experiment, and was intended merely as a model, to try the efficacy of