of the Army of the Potomac, who will cause the necessary examination to be made. The provost-marshal-general will have the custody of all such persons. Division commanders will at once communicate to other division commanders all information thus obtained which affects them.

* * * * * * *

By command of Major-General McClellan:

S. WILLIAMS,

Assistant Adjutant-General.

In addition to the foregoing orders the division commanders were instructed, whenever they desired to send out scouts towards the enemy, to make known the object at headquarters, in order that I might determine whether we had the information it was proposed to obtain, and that I might give the necessary orders to other commanders, so that the scouts should not be molested by the guards.

It will be seen from the report of the chief of the secret-service corps, dated March 8, that the forces of the rebel Army of the Potomac, at that date, were as follows:

Men.

At Manassas, Centreville, Bull Run, Upper Occoquan, and.

vicinity ................................................ 80,000

At Brooks' Station, Dumfries, Lower Occoquan, and vicinity 18,000

At Leesburg and vicinity ................................ 4,500

In the Shenandoah Valley ................................ 13,000

115,500

About 300 field guns and from 26 to 30 siege guns were with the rebel army in front of Washington. The report made on the 17th of March, after the evacuation of Manassas and Centreville, corroborates the statements contained in the report of the 8th, and is fortified by the affidavits of several railroad engineers, conductors, baggage-masters, & c., whose opportunities for forming correct estimates were unusually good. These affidavits will be found in the accompanying reports of the chief of the secret-service corps.

A reconnaissance of the works at Centreville, made by Lieutenant McAlester, U. S. Engineers, on March 14, 1862, and a survey of those at Manassas, made by a party of the U. S. Coast Survey, in April, 1862, confirmed also my conclusions as to the strength of the enemy's defenses. Those at Centreville consisted of two lines, one facing east and the other north. The former consisted of seven works, viz: one battalion fort, two redoubts, two lunettes, and two batteries, all containing embrasures for 40 guns, and connected by infantry parapets and double caponnieres. It extended along the crest of the ridge a mile and three-quarters from its junction with the northern front to ground thickly wooded and impassable to an attacking column.

The northern front extended about one and one-fourth miles to Great Rocky Run, and thence three-fourths of a mile farther to thickly-wooded, impassable ground in the valley of Cub Run. It consisted of six lunettes and batteries, with embrasures for 31 guns, connected by an infantry parapet in the form of a cremaillere line with redans. At the town of Centreville, on a high hill commanding the rear of all the works within range, was a large hexagonal redoubt with ten embrasures..

Manassas Station was defended in all directions by a system of detached works, with platforms for heavy guns arranged for marine carriages, and often connected by infantry parapets. This system was rendered complete by a very large work, with sixteen embrasures, which commanded the highest of the other works by about 50 feet.

Sketches of the reconnaissance above referred to will be found among the maps appended to this report.