I had called upon my friend Sherlock Holmes upon the second morning after Christmas, with the intention of wishing him the compliments of the season. He was lounging upon the sofa in a purple dressing-gown, a pipe-rack within his reach upon the right, and a pile of crumpled morning papers, evidently newly studied, near at hand. Beside the couch was a wooden chair, and on the angle of the back hung a very seedy and disreputable hard-felt hat, much the worse for wear, and cracked in several places. A lens and a forceps lying upon the seat of the chair suggested that the hat had been suspended in this manner for the purpose of examination.“You are engaged,” said I; “perhaps I interrupt you.”“Not at all. I am glad to have a friend with whom I can discuss my results. The matter is a perfectly trivial one”—he jerked his thumb in the direction of the old hat—“but there are points in connection with it which are not entirely devoid of interest and even of instruction.”I seated myself in his armchair and warmed my hands before his crackling fire, for a sharp frost had set in, and the windows were thick with the ice crystals. “I suppose,” I remarked, “that, homely as it looks, this thing has some deadly story linked on to it—that it is the clue which will guide you in the solution of some mystery and the punishment of some crime.”“No, no. No crime,” said Sherlock Holmes, laughing. “Only one of those whimsical little incidents which will happen when you have four million human beings all jostling each other within the space of a few square miles. Amid the action and reaction of so dense a swarm of humanity, every possible combination of events may be expected to take place, and many a little problem will be presented which may be striking and bizarre without being criminal. We have already had experience of such.”“So much so,” I remarked, “that of the last six cases which I have added to my notes, three have been entirely free of any legal crime.”“Precisely. You allude to my attempt to recover the Irene Adler papers, to the singular case of Miss Mary Sutherland, and to the adventure of the man with the twisted lip. Well, I have no doubt that this small matter will fall into the same innocent category. You know Peterson,...