A lecturer whose remarks are going to be published is faced with two audiences, the one that hears him and the one that reads him. Since he hopes and trusts that the second will be the larger and more permanent of the two, he is tempted to write for the eye rather than for the ear. His readers, especially his fellow specialists and the reviewers whose good opinion he wants, loom larger in his mind than the friendly people who come to hear him (even though they come bearing pads and pencils). When his first audience goes home, he hopes that they have taken with them something of what he said, together with an agreeable impression of himself. Still, the fact is that they have dispersed.
A second course for the lecturer is to put his carefully prepared paper to one side and "talk" to his first audience, a solution that can be as unsatisfactory as a relentless reading. A third course is to remove all traces of the lecture hall and to lengthen the book with additional chapters; a fourth is the one that I have chosen to follow, which is to try to write a lecture that will interest both those who hear it and those who read it. Far from trying to decontaminate his printed text by removing every evidence that the book's existence is owing to a lectureship, I think the author should remind his readers occasionally that what they are reading is a lecture written for a particular audience. In any event, the text printed here is virtually the same as the one I read in our National Gallery in February and March 1960, the A. W. Mellon Lectures for that year.
When most of us go to a lecture, we are braced for an hour and . . .