THE Metropolitan Police service has grown, from small and imperfect beginnings, to be a great and effective department of the city government. Many experiments and numerous changes of government and reorganizations have contributed to bring the force to its present efficiency. Twenty-eight years ago, portions of the city were patrolled at night by laborers, porters, cartmen, &c., each carrying a lantern. When a regular police force was at length provided, it fell under the control of corrupt officials and rings, and was of uncertain service to the city, until the Legislature in 1857 took the matter in hand, and provided for the appointment of Police Commissioners, independent of all city control. Since that, the department has rapidly improved in discipline and efficiency until now; but as the new charter of 1870 has again lodged the appointing power in the Mayor of New York, it remains to be seen whether the same untrammeled efficiency in the maintenance of public order shall be continued. The metropolitan district was, until 1870, composed of the cities of New York and Brooklyn, and of portions of Richmond, Kings, and Westchester counties, which were divided into 43 precincts and several sub-precincts. At the close of 1869, there were on duty in New York, 2,232; in Brooklyn, 446; in Richmond Co., 29; and in Westchester, 22; making a grand total of 2,729, including captains, subordinates, and patrolmen. These patroled incessantly about 500 miles of open streets in New York, 350 in Brooklyn, the villages of Yonkers, Tremont, and Morrisania, while a few on horseback scour the suburbs of the two cities mentioned, and others floated around the rivers and bay.

A squad of forty are on service at the various halls of justice, called the Court Squad, and twenty-two are detailed for special service. Four are in charge of the House of Detention, at No. 203 Mulberry street. This is a prison for the detention of witnesses who are to give evidence in the trial of culprits, and one of the rankest legal abominations of New York. During 1869, 194 men and 52 women, or 246 witnesses, were detained in this gloomy tenement an aggregate of 10 years, 7 months, and 13 days. During the seven years just passed, 1,955 persons have here been detained as witnesses, and the aggregate of such detention has amounted to 29,714 days, or nearly 85 years. One poor victim of this oppressive law was detained 269 days awaiting the trial of the case, about which he was supposed to know something, leaving his family, wholly dependent upon him, to suffer every form of destitution. He was an honest mechanic, charged with no crime, but unfortunately knew something of the crimes of others. During 1869, 5 persons were detained over 100 days each, 16 over 60 days each, 25 over 40 days each, and 45 over 20 days each. It is due to the Commissioners to say, that they have again and again appealed to the Legislature for the modification of this system, by allowing the depositions of these witnesses to be taken in due form, after which they might be allowed to return to their homes and occupations.