At New York Public Library, four or five years ago, I heard Rosamond Bernier lecture on Max Ernst. Without notes, standing, she seemed to embrace the whole room into her confidence. Holding a child’s toy tin clicker in her right hand, with a regular snap she commanded the attention of the projectionist who kept up a three-screen slide show.

The thirst for talks on literary and cultural subjects has made such an industry out of the American lecture circuit that experienced professionals like Bernier can accurately target their group. Exactly how much knowledge to assume on the part of the listener (not a great deal), how to tell them