Keaton worked strictly for laughs, but his work came from so far inside a curious and original spirit that he achieved a great deal besides, especially in his feature-length comedies. (For plain hard laughter his 19 short comedies … were even better.) He was the only major comedian who kept sentiment almost entirely out of his work, and he brought pure physical comedy to its greatest heights. Beneath his lack of emotion he was also uninsistently sardonic; deep below that, giving a disturbing tension and grandeur to the foolishness, for those who sensed it, there was in his comedy a freezing whisper not of pathos but of melancholia. With the humor, the craftsmanship and the action there was often, besides, a fine, still and sometimes dreamlike beauty. Much of his Civil War picture The General is within hailing distance of Matthew Brady. And there is a ghostly, unforgettable moment in...