Gradually relics of great crimes began to accumulate there until there are now over six hundred exhibits, ranging over the whole gamut of criminal activity. There is much, perhaps too much, to appeal to the morbid-minded--revolvers by the score, wicked-looking blood-stained knives, hangmen's ropes, plaster casts of murderers taken after death; but more interesting are the tools and equipment of the professional thief and swindler, by which demonstrations are made to raw policemen of the weapons with which his adversaries wage their war upon society. In one case it is an innocent-looking ring, now palpably tarnished brass. But examine it, and you will find that it bears a tolerable imitation of an eighteen-carat hall-mark. When it was fine and bright it was picked up in the street, very ostentatiously, by an astute gentleman who promptly sold it for as much as he could get from a passer-by, who had probably thought it a bargain when he noticed the forged hall-mark. That same trick flourishes to-day, as it flourished over a century ago when Sir John Fielding issued a warning to the public. Close by are a little heap of white sapphires, calculated at one time, with their glitter and dazzle when set as "diamond" rings, to deceive all but the most sophisticated of pawnbrokers. Similarly so, "field-glasses" stamped with the names of famous makers. These are little things, perhaps, but they give the most trusting of young constables some ideas of "ways that are dark and tricks that are vain." Publicans and pawnbrokers seem to be the invariable victims of a certain type of swindler. There is a walking-stick, innocent enough to all appearance, but with a tong-like attachment which, at the touch of a spring, will jump out of the ferrule, enabling a wineglass full of coins to be lifted from a shelf across the counter. A glazed black bag with hinged bottom, which may be placed over any article and automatically swallow it is another ingenious invention. All these, however, are byways of crime. There is much more to be absorbed by the learner in police science. Here he is shown the different types of jemmies, and bars of steel so fashioned that they may be used as chisels or levers. Here are bunches of skeleton keys which, in the hands of experts, will open any ordinary lock in the world. A massive steel implement shaped like a gigantic tin-opener, and used to rip open the backs of safes, is another item in the collection. There are vice-like tweezers which, when properly screwed up, will cut quietly through the bolts of, say, a jeweller's shutters. Still more scientific is a complicated apparatus with tubes in which oxygen and acetylene gas are used to melt through safes with a fierce heat--a quieter, less clumsy, and more effective method than the use of explosives.