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Published online by Cambridge University Press: 20 January 2009
1. If I is an inflexion on a non-singular plane cubic curve, a variable line IPP′ establishes a (1, 1) correspondence between points P, P′ on the curve. This correspondence defines a perspective transformation of the whole plane, with I for pole, and the harmonic polar of I for axis, of perspective; for, when I is projected to infinity on the y-axis, and its harmonic polar taken for x-axis, the resulting equation
indicates a curve symmetrical with respect to the latter.
* Cf. Baker, , B. A. Report 1910 (Sheffield), p. 528.Google Scholar