Appleton's cyclopaedia of drawing : designed as a text-book for the mechanic, architect, engineer, and surveyor : comprising geometrical projection, mechanical, architectural, and topographical drawing, perspective and isometry (1869)
Worthen, W. E. (William Ezra), 1819-1897 · New York : D. Appleton and Company · leaf 26
GEOMETRICAL DEFINITIONS AND TECHNICALITIES. 5 PF is always equal to PD=. F is called the focus , and the line KIP the directrix (fig. 21). K JD Fig. 21. Fig. 22. An hyperbola is a curve from any point P in which, if two straight lines be drawn to two fixed points FF' the foci, their difference… … Fig. 24. a circle which rolls along an extended straight line until it has completed a revolution. If the circle be rolled on the circumference of another circle, the curve then described by the point P is called an epicycloid (fig. 24). Epicycloids are external or internal , according as the…
