Page:A Dissertation on the Construction of Locks (1785).pdf/24

 aware, and as ſenſible as I am of the impoſſibility of guarding the avenues to the bolt ſo effectually by, as to prevent all acceſs to it; for leaving the entrance and paſſage, to the common protection of wards and outworks, his ingenuity hath been wholly applied to the interior fortification of the bolt, by a new and judicious application of additional tumblers. Theſe are a kind of grapple by which the bolt is confined as well in its active as its paſſive ſtation, and rendered immoveable, till ſet at liberty by the key. One of theſe inſtruments is commonly introduced into all Locks that are of any uſe or value; it is lodged behind the bolt, and is governed by a ſpring which acts upon the tumbler, as the tumbler acts upon the bolt. The application therefore of any force to the tumbler, which is ſuperior to the force of the ſpring, will cauſe it to quit its hold, and ſet the bolt at liberty. And in this operation no ſkill or nicety is required, to