Pocketbook of Useful Formulæ and Memoranda
for Civil and Mechanical Engineers

OF ENGINEERING FORMUI,Æ. C ubves—con t inned. a = Diameter of generating circle. x = Abscissa. y = Ordinate. To construct a cardioids curve describe the generating circle and through one end of its diameter draw radiating lines, always making b bb — a. The equation to the curve is as follow s :—■ Caedioide. yi— Gai/3 + 2x?y2— 6ax^y + x*+12 u2i/2—8u3t/ + 3a?z-=0. x = Abscissa. y Ordinate, a = Axis. _ X — X* Lemniscatb. Sl’IBAL. TRUE »PIRAL. FALSE SPIRAL. Divide the radius and the circumference into the same number of equal parts, then the intersection of the radial Itoi s gives points in the curve. A fabe spiral is sometimes drawn in a series of quadrants from four centres. 3/ = = • 159 æ. 7T