Thieves are numerous in New York. As a general rule, they herd together in the worst quarters of the city - in the Five Points and along East River - where they can rapidly and easily communicate with each other, and where they can hide from the police without fear of discovery. There are many blunderers in the fraternity, but there are also many experienced hands, who do a great deal of damage, and give a world of trouble to the authorities. These are generally well known to the police.

                     THE THIEF LANGUAGE.

The thieves of the city have a language, or argot, peculiar to themselves. Those who have been raised to the business use this argot to such an extent, that a stranger finds it as impossible to understand them as he would if they were speaking in a foreign tongue. The Detectives' Manual gives a glossary of this language, from which we take the following specimens, to be found in that work, under the head of the letter B.:

Badger. - A panel-thief.

Bagged. - Imprisoned.

Bag of nails. - All in confusion.

Balram. - Money.

Bandog. - A civil officer.

Barking irons. - Pistols.

Bene. - Good, first-rate.

Benjamin. - A coat.

Bilk. - To cheat.

Bill of sale. - A widow's weeds.

Bingo. - Liquor.

Bingo boy. - A drunken man.

Bingo mort. - A drunken woman.

Blue-billy. - A strange handkerchief.

Blue ruin. - Bad gin.

Boarding-school. - The penitentiary.

Bone box. - The mouth.

Bowsprit in parenthesis. - A pulled nose.

Brother of the blade. - A soldier.

Brother of the bolus. - A doctor.

Brush. - To flatter, to humbug.

Bug. - A breast-pin.

Bugger. - A pickpocket.

Bull. - A locomotive.

Bull-traps. - Rogues who personate officials to extort money.

We could multiply these examples, but the above are sufficient to illustrate this branch of our subject.

                     PROFESSIONAL THIEVES.

The poor wretches who steal a few dollars' worth in open day, from stores and stands, are not considered by professional thieves as amongst the "fraternity," which embraces house-breakers, pick-pockets, and burglars. These persons are carefully trained by "old hands," and are by practice made as perfect as possible in their arts. Indeed, to be an accomplished burglar requires a very great degree of intelligence, courage, strength, and ingenuity. These men all have certain distinct methods of performing their work, so that after they have been operating a short while, a detective can, by examining the traces, tell, with absolute certainty, the name of the burglar. Besides this, the life which these persons lead stamps their countenances and general bearing with marks which an experienced officer will recognize at a glance. The sneak-thief, the pickpocket, and the burglar, have certain habits, attitudes, haunts; they act in certain ways when placed in certain positions, which reveal them and their occupations to a practiced eye, with almost as much certainty as the form and aspect of a blade of grass reveals its genus and species to the eye of a practiced botanist. A skilled detective will stand at the corner of a street, in a strange city, that he has never entered before, and will pick out, almost unerringly, the passers-by who belong to this criminal class. He will say, "This is a sneak-thief;" "This is a pickpocket;" "This man has just been released from the State prison;" "This one is a gambler, stool-pigeon," etc., etc.; being guided in his judgments by certain indications which the criminal involuntarily displays by the sheer force of habit.

A sneak-thief will pass along with that rapid, rolling glance of the eyes which distinguishes the tribe; now he checks himself in his career; it is but for an instant; no unprofessional eye directed towards him would notice it; but the sudden pause would speak volumes to an experienced police officer. He knows that the thief's eye has caught the sight of silver lying exposed in the basement. In an hour after he hears that the basement has been entered, and the silver in it carried off. He knows who has taken it, as well as if he had seen the man take it with his own eyes; but if the thief has had time to run to the nearest receiver's den, the silver is already in the melting-pot, beyond the reach of identification.

                     HOW FINE HOUSES ARE ROBBED.

Families living in the city cannot, of course, know who they are taking into their midst as servants, and it frequently happens that these girls are the confederates of burglars. They come for the purpose of spying out the premises, and from time to time report the internal arrangements to their "men." At the proper moment, the burglar, who has thus acquired a sufficient familiarity with the house, is admitted by the girl. He performs his work sometimes without detection, but sometimes adds murder, or attempts at murder, to his crime. These men are well known to the police, but as they are to be deemed innocent untilproved guilty, it is hard, if not impossible, to prevent their crimes. A servant girl is seen in the area, towards evening, with a broom in her hand; by her side is a man who is conversing earnestly with her. The policeman, as he passes along, recognizes him as a notorious burglar. That night the house is broken open and robbed, and perhaps some of the family murdered. The officer knows perfectly well who did it, but this knowledge goes for nothing in law. The man must be regularly tried, and proved guilty. Although the officer feels sure the man and woman are planning a burglary, when he sees them in the area, he cannot prevent it by arresting the man.

An incident in point has transpired of late, in illustration of this familiar danger. A gentleman's house, situate on Fifth Avenue, near Thirty-second street, was entered on the night of March 24th, by a brace of burglars, who were, as subsequent investigation proved, admitted at the basement, or servant's entrance, by one of the chambermaids.

The burglars succeeded in obtaining a considerable amount of plunder, but were alarmed by the unexpected awakening of some of the inmates of the house, and hastily departed. Suspicion fell upon the delinquent maid, who was examined, confessed her guilt, stated that the principal burglar was her sweetheart, and promised that if she was permitted to escape the deserved public punishment of her crime, she would see that the missing property was restored to its rightful owners. This 'arrangement' was accepted, the girl fulfilled her part of the contract, and every article that had been stolen was promptly restored. The chambermaid was dismissed, and any further prosecution of the affair was summarily closed. In this particular instance, it will be seen that matters terminated favorably, but it would be well if wealthy citizens would be warned against the 'family' risk to which their property is exposed, and led to adopt the most stringent precautions against these dangers, especially when summer pleasures will entice the majority of the votaries of gayety and fashion 'out of town,' leaving their dwellings almost wholly to the 'care' of not always reliable domestics.

                     A HAIR THIEF.

During the summer of 1868, a young lady residing in a respectable part of the city, was decoyed by an elderly woman, (under the pretence of being able to introduce the young lady to a cheap dressmaker,) into a low neighborhood, where she was seized by two men, dragged into a hovel, and there held by the ruffians, while the old hag who had decoyed her thither, with a pair of shears cut off the larger portion of her luxuriant hair - to fill, as she coolly informed her victim, 'an order from a wig-maker.' The screams and struggles of the poor dupe were of no avail, and when finally thrust out of doors by her tormentors, she was so frightened that she wandered mechanically along, up and down streets, until she met a policeman, who, on hearing her story, called a carriage and had her conveyed home, but was not able from her incoherent and inaccurate description, either to identify the place where the outrage was committed, nor the people by whom it was perpetrated.

                     THE THIEVES' EXCHANGE.

There is, in the Eighth Ward of the City, an "Exchange," where the light-fingered gentry congregate and interchange confidential intelligence, the news of their profession, and exchange the stolen goods temporarily in their possession. Attached to this is the wareroom of the proprietor, who is simply a receiver of stolen goods. There are many of these places in the city.

The agent of the New York Prison Association, in one of his reports, says:

When a burglar has successfully entered a store, and carried off a large amount of property, in the form of fine goods, this property itself is of no more use to him than the dust of the street. He does not want to wear lace or jewelry. He does not need watches or pencil-cases. He cannot eat cameos or vases. He, therefore, at once takes his plunder to his 'fence,' and receives from him, in money, such a price as is usually agreed upon. It is very difficult to ascertain, with any degree of exactness, what proportion of the value of the plunder is realized on the average by the thief; but from the best information we could obtain, we feel confident it does not exceed one sixth.

A man whom we met in one of the jails, told us he was unsuccessful at first, because he had received no instructions in the art. We asked him what he deemed the most important information to be obtained by a tyro in the business. He answered promptly: 'To know the names and characters of all the "fences" within a circle of thirty miles.' He could do little or nothing without this knowledge.

In the rural districts, these receivers of stolen goods are quite unknown, except among the thieves themselves, unless some unusually active deputy sheriff makes the discovery; but in the cities, especially in New York and Brooklyn, they are as well known to the police officers as the city halls of those places. These officers are sure that everything they have in their warehouses is stolen; they are acquainted with their ways of doing business; and they know what thieves resort to each, and where they dispose of their ill-gotten property. Yet this knowledge avails but little in promoting the ends of justice. It is but rarely that any of this class are convicted of their offences. The reason is that strict legal proof of their guilt can very seldom be procured.

The study of the means of rapidly and effectually removing the marks by which the property in their hands can be identified, is the main business of their lives, and they acquire a degree of skill and dexterity in altering or effacing these marks, which is truly surprising. A melting-pot is always over the fire, to which all silver ware is consigned the instant it is received. The marks on linen, towels, and handkerchiefs, are removed, sometimes by chemicals, sometimes by fine scissors made expressly for the purpose. Jewelry is at once removed from its settings, and the gold is either melted or the engraving is burnished out, so as in either case to make identification impossible. Rich velvet and silk garments are transmogrified by the removal and re-arrangement of the buttons and trimmings. Pointed edges are rounded, and rounded edges are pointed, entirely changing the whole aspect of the garment, with such celerity that the lady who had worn the dress in the morning would not have the slightest suspicion that it was the same in the evening. Cotton, wool, rags, and old ropes, require no manipulation. When once thrown upon the heap, they defy the closest scrutiny of the owners. There is scarcely an article which can be the subject of theft, which the resources of these men do not enable them, in a very short time, to disguise beyond the power of recognition. Their premises are skilfully arranged for concealment. They are abundantly provided with secret doors and sliding panels, communicating with dark recesses. Apertures are cut in the partitions, so that a person coming in from the front can be distinctly seen before he enters the apartment. The 'fence' is as well skilled as any lawyer in the nature of evidence. He knows the difference between probability and proof as well as Sir William Hamilton himself. He does not trouble himself about any amount of probabilities that the detectives may accumulate against him; but the said detective must be remarkably acute if he is ever able to get anything against him which will amount to strictly legal proof.