Page:A Dissertation on the Construction of Locks (1785).pdf/46

 or inſtrument, by which a Lock, conſtructed on this principle, can be opened.

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 levers being raiſed, by the ſubjacent ſprings, to an equal height in the frame B, 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 levers will then exhibit, can be taken; the workman will, in vain, attempt to fit a key to the Lock; or, by any effort of art, to move the bolt. And when it is conſidered, that this proceſs will be greatly ,