In earlier volumes of the Proceedings of the Edinburgh Mathematical Society (cf. III., 104; IX., 83) it has been shown by researches of Dr. J. S. Mackay that the “discovery of the Wallace line … dates back only to about the year 1799 or 1800.” This result is reproduced in Cantor's Vorlesungen über die Geschichte der Mathematik (III., 542, 2te Aufl.). It was arrived at by considering the two following theorems given by Professor Wallace in the old series of Leybourn's Mathematical Repository:

Theorem A (Vol. I., p. 309 ; Vol. II., p. 54–5). If three straight lines touch a parabola, a circle described through their intersections shall pass through the focus of the parabola.