Some twenty-five years ago I was in the unpleasant position of “professing” Geometry, with (roughly) six weeks start of the class; it is no disparagement to the abilities of the Galway Honour Students to confess (at this late hour) that—however hard put to it—I never had reason to admit greater ignorance than that of the class. Amongst other things I was obliged to learn that there is a certain projective relation between the 27 lines on a cubic surface and the 28 bitangents to a (general) plane quartic; this fact impressed me so much that it remains (also a general idea of where a proof can be found) even now, when my memory has discarded many things which are (perhaps) more vital.