A story is told of Professor Benjamin Peirce that it was his custom to invite members of his sections in Higher Mathematics to question him after the recitation in regard to any explanations he made that were not perfectly understood. One of the students took advantage of this invitation one day and went up to the desk for the purpose of clearing up in his mind a doubtful point. To his surprise, the venerable professor received his question in silence. It was repeated again. Still no response. "But did you not invite us to ask you questions in regard to your lecture, sir?" inquired the student. "Oh, certainly," replied Professor Peirce, with an air of surprise, "but I meant intelligent questions."