Linkwoyk in GeneralThe pieces which are connected by linkwork, if they rotate or oscillate, are usually called cranks, beams and levers.
Intermittent LinkworkClick and Ratchet.A click acting opon a ratchet-wheel or rack, which it pushes or pulls through a certain arc at each forward stroke and leaves at rest at each backward stroke, is an example of intermittent linkwork.
During the forward stroke the action of the click is governed by the principles of linkwork; during the backward stroke that action ceases.
The notions of distance and of lines at right angles are connected with the circular points; and almost every construction of a curve by means of lines of a determinate length, or at right angles to each other, and (as such) mechanical constructions by means of linkwork, give rise to curves passing the same definite number of times through the two circular points respectively, or say to circular curves, and in which the fixed centres of the construction present themselves as ordinary, or as singular, foci.