I have read many presidential addresses. Science publishes something like 52 of them annually. I have also listened to a few. Most of them are characterized by a more or less lucid, and usually very readable, narration of events, discoveries, and theories which mark the progress of the various sciences. In these the audience is presumed to be familiar with the subject-matter of the address, to have first-hand knowledge of the events, to have made the discoveries, and to have formulated the theories which are set forth. In this case the attention of the audience never flags, since it is never strained. The listener amuses himself by running ahead of the speaker, anticipating what he will say next, and keeping himself in the best of humor by finding his anticipations realized. This type of address is thus a literary effort rather than a contribution to the particular science concerned. As . . .