Page:A Dissertation on the Construction of Locks (1815).pdf/27

 fortifications of the bolt, by a 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 ascertain the degree of force to be applied; for, it matters not how far the tumbler is lifted above the point, at which it ceases to controul the bolt. But Mr. Baron has improved upon the practised method of applying the tumbler, by confining their action within a circumscribed space, cut in the center of the bolt, of a dimension barely sufficient to the purpose they are intended to answer, and which space is provided with niches on the upper side, as well as the lower, into which the hooks are driven, if any greater force be applied to the tumblers, than is required to disengage them from the bolt. Hence