Practical plane and solid geometry for advanced students, including graphic statics, adapted to the requirements of the South Kensington syllabus (1899)
Harrison, Joseph, Baxandall, George Albert · London Macmillan · leaf 136
curve, or the two curves are parallel to one another;they are equidistant at all points when measured normally.Otherwise, if a circle move with its centre on any curve,the envelope of the circle is a curve parallel to the firstcurve. This second definition indicates the practicalmethod usually… … A curve parallel to a circle is a concentric circle, andthat parallel to a straight line is a second straight line. Inall other cases the parallel curve is of a different character-fromthe original one. Thus the parallel curve to an ellipse isnot an ellipse. This is seen very clearly in the…
