If Porter effects a lodgment on both railroads near Hanover Court-House, consider whether your forces in front of Fredericksburg should not push through and join him.

A. LINKOLN.

WASHINGTON, May 28, 1862 - [2 p. m.]

General MCDOWELL,

Manassas Junction:

General Saxton's dispatch, received at 1.5 p. m., reports intelligence from General Banks that two regiments cavalry and some infantry were at Martinsburg; that a prisoner states that Ashby was ordered to Winchester yesterday morning, and withdrew with part of his cavalry and more artillery. General Banks says he shall occupy Falling Waters to-day, and believes that enemy is still strong at Winchester.

EDWIN M. STANTON,

Secretary of War.

MANASSAS, May 28, 1862.

(Received 2.10 p. m.)

Honorable E. M. STANTON:

Brigadier-General Kimball, commanding advance brigade of Shield's division, reports as follows from Thoroughfare Gap:

9 a. m.- I am in the Gap. My advance guard is beyond. The railroad is all right. So far all is moving very well. I will go to White Plains if not checked or counter-manned by your order. I hear nothing of rebels having been seen in this vicinity. There is a large amount of camp equipage of the One hundred and fourth New York Volunteers here.

IRVIN MCDOWELL,

Major-General, Commanding.

WASHINGTON, May 28, 1862 - 2.37 p. m.

General MCDOWELL, Manassas:

The following information is received, at 2.20 p. m., from the president of the Baltimore and Ohio Railroad:

Enemy yesterday afternoon at Martinsburg with artillery, infantry, and cavalry. Yesterday evening occupied Kearnesville, Smithfield, Charlestown, and drove in our picket from Halltown. The pickets of two companies driven in from Loudoun Heights last night; 1 man killed, 2 wounded. A reconnaissance in force - one regiment infantry, one of cavalry, and two pieces of artillery - just started for Charlestown. Colonel Miles informs me he last night ordered Colonel Campbell, Fifty-fourth Pennsylvania, who is at South Branch, to reoccupy the railroad to Hancock, and to Back Creek if he can do so. The big gun planted on Maryland Heights has been throwing shell on Loudoun Mountain this morning. A white flag has just been run up on Loudoun Heights.

Our agent reports from Point of Rocks refugees crossing river, who report the enemy's cavalry at Leesburg, Waterford, and other posts in Loudoun, and ask that a company of soldiers be sent down. Colonel Miles has ordered one company of Maulshby's regiment down. They are now getting on the cars. It is probable that a raid might be attempted to destroy Monocacy Brodge, by which means rapid re-enforcements, should they be required, would be cut off. I beg to suggest that it is important that point should be strongly guarded.

J. W. GARRETT,

President Baltimore and Ohio Railroad.

This is the latest received.

EDWIN M. STANTON.