WASHINGTON, August 29, 1862 - 1.20 a. m.

General GEORGE B. McCLELLAN, Alexandria:

There are two regiments at the Chain Bridge. Two others are ordered from near Tennallytown, but this will unman the forts from Fort Pennsylvania to Forts Alexander and Ripley. General Casey will send two others from Hunter's Chapel, which will not arrive till morning, late.

I think a force with artillery should be sent up to take post on this side of the bridge.

J. G. BARNARD,

Brigadier-General.

ALEXANDRIA, August 29, [1862] - 2 a. m.

(Received 3 a.m.)

General J. G. BARNARD:

Your dispatch received. I have ordered two regiments and a battery to proceed at once up this side of the river to the Cahin Bridge, and I have told the Officer who sends them (General Sumner) that you would have an officer there to post them. I would advise you to hold the works as long as you can with safety, and at the same time be prepared to destroy the bridge as short notice.

GEO. B. McCLELLAN,

Major-General.

ARLINGTON, August 29, 1862 - 6.30 a. m.

General BARNARD:

General Casey's two regiments are en route to Chain Bridge. Two others have reported to me, one the One hundred and twentieth New York, with 5 rounds of ammunition and more drawn and on its way. Send immediately to Chain Bridge the other regiment. The Ninth New Hampshire has no ammunition except what is supposed to be on the way from the arsenal. This regiment will wait at Fort Corcoran for its ammunition. Shall I then send it to Chain Bridge or let it remain at Fort Corcoran?

A. W. WHIPPLE,

[Brigadier-General.]

ALEXANDRIA, VA., August 29, 1862 - 9.15 a. m.

General J. G. BARNARD:

The general commanding directs me to say that the Fourteenth Massachusetts Volunteers, a well-drilled heavy artillery regiment, is at your disposal. It is now coming in. The general wishes it posted in the most important works,beginning with Forts Marcy and Ethan Allen, on the right.

S. WILLIAMS,

Assistant Adjutant-General.