To the Metropolitan Police Force.

On the morning of Monday, the 13th inst., the peace and good order of the city were broken by a mob collected in several quarters of the city, for the avowed purpose of resisting the process of drafting names to recruit the armies of the Union.

Vast crowds of men collected and fired the offices where drafting was in progress, beating and driving the officers from duty.

From the beginning, these violent proceedings were accompanied by arson, robbery, and murder.

Private property, unofficial persons of all ages, sexes, and conditions, were indiscriminately assailed—none were spared, except those who were supposed by the mob to sympathize with their proceedings.

Early in the day the Superintendent was assaulted, cruelly beaten, robbed, and disabled by the mob which was engaged in burning the provost marshal's office in Third Avenue, thus in a manner disarranging the organization at the Central Department, throwing new, unwonted, and responsible duties upon the Board.

At this juncture the telegraph wires of the department were cut, and the movement of the railroads and stages violently interrupted, interfering seriously with our accustomed means of transmitting orders and concentrating forces.

The militia of the city were absent at the seat of war, fighting the battles of the nation against treason and secession, and there was no adequate force in the city for the first twelve hours to resist at all points the vast and infuriated mob. The police force was not strong enough in any precinct to make head, unaided, against the overwhelming force. No course was left but to concentrate the whole force at the Central Department, and thence send detachments able to encounter and conquer the rioters. This course was promptly adopted on Monday morning. The military were called upon to act in aid of the civil force to subdue the treasonable mob, protect life and property, and restore public order.

Under such, adverse circumstances you were called upon to encounter a mob of such strength as have never before been seen, in this country. The force of militia under General Sandford, who were called into service by the authority of this Board, were concentrated by him at and held the arsenal in Seventh Avenue, throughout the contest. The military forces in command of Brevet Brigadier-general Harvey Brown reported at the Central Department, and there General Brown established his head-quarters, and from there expeditions, combined of police and military force, were sent out that in all cases conquered, defeated, or dispersed the mob force, and subjected them to severe chastisement. In no instance did these detachments from the Central Department, whether of police alone or police and military combined, meet with defeat or serious check.

In all cases they achieved prompt and decisive victories. The contest continued through Monday, Tuesday, Wednesday, Thursday, and till 11 o'clock on Thursday night, like a continuous battle, when it ended by a total and sanguinary rout of the insurgents.