The verge (or crown wheel) escapement is the earliest known type of mechanical escapement, the mechanism in a mechanical clock that controls its rate by allowing the gear train to advance at regular intervals or 'ticks'.he verge (or crown wheel) escapement is the earliest known type of mechanical escapement, the mechanism in a mechanical clock that controls its rate by allowing the gear train to advance at regular intervals or 'ticks'.
You need the foci for some construction methods. Just draw radii of length a from the ends of the minor axis. Given the foci, however, you can't uniquely determine the axes. You need additional information such as the length of one axis.
An ellipse has two foci. The sum of the distances from any point on the ellipse to the two foci is the same for every point on the ellipse. In figure 1, we show an ellipse in which the foci are 1.7 units apart, and in which the sum of the distances to the two foci is 2 for every point on the ellipse. Figure 1 -- An Ellipse, with foci at +/- 0.87, sum of radii = 2: