Page:A Dissertation on the Construction of Locks (1785).pdf/43

 part E, which is a thin plate, bearing at each extremity on a block, and having of courſe a vacant ſpace beneath, equal in height, to the thickneſs of the blocks on which it reſts. This plate is applied either to check, or to guide the motion of the machine; and theſe oppoſite offices are thus performed.—On the edge of the plate, which faces the movement, ſix notches are expreſſed, into which the points of the levers, projecting beyond the frame B, are received; and whilſt they are ſo confined, the motion of the machine is totally ſuſpended, and the bolt ſo fixed, as to defy every effort of art, or force, to move it.—The neceſſity of the proper key, to the purpoſe of opening this Lock; and the impoſſibility of effecting it by other means, will be clearly ſeen from the proceſs, by which the machine is put in motion. It is to be obſerved, that each lever has a notch expreſſed on its extreme point; and, that thoſe notches are diſpoſed as irregularly