Page:A Dissertation on the Construction of Locks (1785).pdf/41

 of the principle; but, to my great admiration, it turned out a complete inſtrument of ſecurity; and gave the cleareſt demonſtration, that the principle was certain and infallible.

Plate the firſt.—The lines, which croſs the face of the Lock, repreſent ſix levers, which are united in a joint, and turn on a common axis, at the point A. Each lever reſts on a ſeparate ſpring, of ſufficient ſtrength to ſuſtain its weight, or, if depreſſed by a ſuperior force, to reſtore it to its proper poſition, when that force is withdrawn. The curve B repreſents a frame, through which the levers are carried by ſeparate grooves, or paſſages; theſe grooves are exactly fitted in their width, to the thickneſs of the levers, but are of ſufficient length, to allow them a free motion, in a perpendicular direction, whether