THE happily ignorant reader, whose knowledge of the criminal classes is confined to an occasional glance through the police court and Sessions cases as narrated in his morning newspaper, will be shocked and amazed to learn that within the limits of the City of London alone, an army of male and female thieves, twenty thousand strong, find daily and nightly employment. It is easy to write “twenty thousand,” and easier still to read the words. Easier than all to pass them by with but a vague idea of their meaning, and perhaps a sympathetic shrug of the shoulders for the poor, hard-worked policemen who must have such a terrible time of it in keeping such an enormous predatory crew in anything like order. Still, and without the least desire to be “sensational,” I would ask the reader, does he fully comprehend what twenty thousand thieves in London means? Roughly estimating the population of the metropolis as numbering three millions, it means that amongst us one person in every hundred and fifty is a forger, a housebreaker, a pickpocket, a shoplifter, a receiver of stolen goods or what not; a human bird of prey, in short, bound to a desperate pursuit of that terrible course of life into which vice or misfortune originally casts him; a wily, cunning man-wolf, constantly on the watch, seeking whom he may devour. Almost every member of this formidable host is known to the “police,” but unfortunately this advantage is almost counterbalanced by the fact that the police are as well known to the majority of the twenty thousand. To their experienced eyes, it is not the helmet and the blue coat that makes the policeman. Indeed, they appear to depend not so much on visual evidence as on some subtle power of scent such as the fox possesses in discovering the approach of their natural enemy. They can discover the detective in his innocent-looking smock-frock or bricklayer jacket, while he is yet distant the length of a street. They know him by his step, or by his clumsy affectation of unofficial loutishness. They recognise the stiff neck in the loose neckerchief. They smell “trap,” and are superior to it. There is a language current amongst them that is to be met with in no dictionary with which I am acquainted. I doubt if even the “slang dictionary” contains more than a few of the following instances that may be accepted as genuine. It will be seen that the prime essential of “thieves’ latin” is brevity. By its use, much may in one or two words be conveyed to a comrade while rapidly passing him in the street, or, should opportunity serve, during a visit to him while in prison. To erase the original name or number from a stolen watch, and substitute one that is fictitious—_christening Jack_. To take the works from one watch, and case them in another—_churching Jack_. Poultry stealing—_beak hunting_. One who steals from the shopkeeper while pretending to effect an honest purchase—_a bouncer_.