In Vol. XXXV. (Session 1916–17), Part I., of the Proceedings of the Edinburgh Mathematical Society, I discussed in considerable detail the properties of the Apolar Locus of two tetrads of points. I showed there that, subject to certain defined conditions, a unique quartic curve would be obtained, which would be the Apolar Locus of the two given tetrads. I mentioned, however, in §7 of the paper, that in the case when the two tetrads lie on the same conic, the above-mentioned conditions are not independent, and that, in fact, not a unique quartic but a pencil of quartics is obtained.