Page:A Dissertation on the Construction of Locks (1785).pdf/44

 irregularly as poſſible. To give a capacity of motion to the machine, theſe notches muſt be brought parallel to each other, and, by a diſtinct, and unequal preſſure upon the levers, be formed into a groove, in a direct line with the edge of the plate E, which, the notches are exactly fitted to receive. The leaſt motion of the machine, whilſt the levers are in this poſition, will introduce the edge of the plate into the groove; which, controling the power of the ſprings, will give liberty to the levers to move in an horizontal direction, as far as the ſpace between the blocks, which ſupport the plate E, will admit, and which is ſufficient to give the machine a power of acting on the bolt.—The impoſſibility of thus bringing the notches, expreſſed on the points of the levers, to fall into a direct line, and to form a groove, which ſhall perfectly tally with the edge of the plate E, by any other means, than the application and impulſe of the key, is the principle