The Sanitary Squad consists of a captain, four sergeants, and fifty-seven patrolmen. A detachment of these look after the safety and workings of the numerous ferry lines communicating with New York, and tell us that about ninety million people cross on these lines to or from the metropolis in a year. Others test hydrostatically at intervals, and by Nurse, every steam boiler on the island; causing defective ones to be repaired or removed. They examine and license suitable persons as engineers. Others execute the orders of the Board of Health. Still another detachment looks after truant children, compelling thousands to return to school, and conveying some to the Juvenile Asylum. Some members of the Sanitary Squad have ranked among the most pious, benevolent, and useful men of New York. The Detective Squad consists of a captain and nineteen subordinates. These are all shrewd, adroit, and skillful men of good reputation, whose business it is to unravel the deepest schemes, ferret out the darkest crimes, and entrap the shrewdest villains. Their knowledge of polite thieves, counterfeiters, forgers, and burglars, is very extensive. Great thieves are continually watched by them, so that they know at once whether they were in a city at the time of a robbery or not. They scent crime across a continent, even across the ocean. A man hitherto considered reputable is arrested for forgery or burglary, and it comes to be known that the detective can tell how much money his wife has expended in the city for twelve months. Though living in private quarters all her movements have been watched, and all her purchases ascertained and recorded. They grasp at every clue, and follow it to its result, often discovering the perpetrator of crime from the slightest accident. When men who have spent their money set up the plea of having been robbed, the detective is sure to search them out, and expose them. Millions of dollars worth of stolen goods are annually recovered by this force, but with all their art, some great rogues escape. Horrible murders and bold robberies remain veiled in impenetrable mystery. Much of this detective work is performed by the " Merchants' Independent Detective Police," established in 1858, and by members of the several other detective organizations.

The headquarters of the Police department are a fine marble structure, at No. 300 Mulberry street, containing elegant offices for all the officials, with telegraphic communications with every station-house in the department; rooms for the instruction of candidates for the force, and for the trial of offenders. The Commissioners are very strict with the members of the force, fining and discharging many for dereliction, intemperance, or other vicious habits. The pay of a patrolman is $1,200 per annum, but as he has no Sabbath, or other privileges, such as most men enjoy, his compensation is not large. Men are selected and distributed according to their fitness for the different undertakings. The tallest are stationed along Broadway, those with mechanical knowledge tend toward the Sanitary, and those of penetration and adroitness, toward the Detective squads. Their appearance is always that of tidy, well-dressed, courteous officers, erect and manly in bearing, and in the prime of life, the average age being about thirty-five years.

During the last nine years, the police have returned over 73,000 lost children to their parents or homes, and found above 40,000 houses left open, through the carelessness of inmates, affording unembarrassed opportunities for the entrance of thieves and burglars. That policemen are sometimes rash, unduly severe and evil, we doubt not; yet the regulations and discipline of the department are so severe, as to render them generally effective, and without them nothing would be safe for a day. They are distinguished for their valor, and their numerous bloody encounters with rioters, and villains of every grade, are well known and startling. During 1869 they arrested no less than 56,784 males, and 21,667 females, making a total of 78,451.