Conic Foci Involution Small 320×189 Medium 640×377 Large 1024×603 Download Tiff Original 2400×1414 | (176.4 KB) Description The lines joining any point on a conic to the two foci are equally inclined to the tangent and normal at that point. This is an ellipse. Keywords circle, conic, conic section, ellipse, foci, section, tangent Galleries Conic Sections: Ellipses Source: Encyclopaedia Britannica (New York: The Encyclopaedia Britannica Company, 1910) 11:703
