Page:A Dissertation on the Construction of Locks (1815).pdf/44

 round, moves in the direction of the dotted circle, and of course carries the bolt to and fro, with it. The pin v, is attached to the covering plate, and serves to steady the bolt in its motion. The principle of security is thus made to restrain the bolt without the intervention of any other agent; and the slightest inspection must convince, that no power can move the bolt, but that which also puts in motion the barrel.

Fig. 9, is the appearance of a Drawer Lock in its complete state.

It will be a task indeed of great difficulty, even to a skilful workman, to fit a key to this species of Lock, though its interior face were open to his inspection; for the sliders being raised, by the subjacent spring, to an equal height iv the barrel, present a plane surface; and, consequently, convey no direction, that can be of any use in forming a tally to the irregular surface, which they present, when acting in subjection to the proper key. Unless, therefore, a method be contrived to bring the notches, expressed on the extreme points of the levers, in a direct line with each other, and to retain them in that position, till an exact impression of the irregular surface, which the sliders will then exhibit, can be taken; the