Under such chiefs as these the rank and file of our detectives labour, assiduously utilising the qualities which really serve them best--patience and persistence, following the hints and suggestions given them by their leaders. The best detective is he who has that infinite capacity for taking pains which has been defined as the true test of genius. It is not by guesses or sensational snapshots that crimes are unearthed, but by the slow process of routine, almost commonplace inquiry, after the most minute and painstaking investigation of the traces--often of the most minute character--left upon the theatre of the deed. [Illustration: MR. MCWILLIAM.] People whom business or chance has brought much into contact with detectives must have been struck with their ubiquity. All who have a good memory for faces or the vision to penetrate disguises will have had many opportunities of recognising them in strange places and at unexpected times. The police officer is to be met with in railway trains, on board steamboats, in hotels, at all places of public resort. He may [Illustration: NEW SCOTLAND YARD. 1. Commissioner's Room. 2. View from the River (_Photo: York & Son, Notting Hill, W._). 3. Principal Entrance. 4. The Western Façade. ] be seen in "the rooms" at Monte Carlo, retained by "the administration" of the casino to keep his eye on the company, or engaged on business of his own, "shadowing" some criminal or suspect. I have given my coat and hat to a detective at a great London reception in an historic house, where many of the guests were titled or celebrated people, but into which others, unbidden and extremely undesirable, had been known to insinuate themselves in the prosecution of their nefarious trade. I have met detectives at a wedding breakfast, at a big dinner, at balls during the season, and I can safely assert that these "professionals," in manners or in costume, were certainly not the least gentlemanlike of the guests assembled. There is no better company than a good detective, if he can only be persuaded to talk--no easy matter, for reticence is a first rule of conduct in the profession, and he is seldom communicative except on perfectly safe ground. It was my good fortune once to be thrown with a well-known member of one of those provincial forces which include many first-rate detective practitioners. It was some years back, and I am committing no breach of confidence in recounting some of his experiences. "Never let go, sir: that's the only rule. I like to keep touch of 'em when once I've got 'em," he began, and he spoke pensively, as though his mind were busy with the past, and he rubbed his hand thoughtfully over his chin.