Mr Ridley's note in the January number giving an algebraic explanation of extraneous values suggests an elementary treatment of the subject on the geometrical side. It must be assumed that the pupil is able to trace from their equations straight lines, circles, and parabolas of the type y = ax2 + bx + c. He should be made to draw the curves in cases like those given here, and to state the geometrical meaning of every distinct step in the algebra.