On the 12th I received the following telegram from His Excellency the President:

Governor Curtin telegraphs me, "I have advices that Jackson is crossing the Potomac at Williamsport, and probably the whole rebel army will be drawn from Maryland."

The President adds:

Receiving nothing from Harper's Ferry or Martinsburg to-day, and positive information from Wheeling that the line is cut, corroborates the idea that the enemy is recrossing the Potomac. Please do not let him get off without being hurt.

On the 13th General Halleck telegraphed as follows:

Until you know more certainly the enemy's force south of the Potomac you are wrong in thus uncovering the capital. I am of the opinion that the enemy will send a small column toward Pennsylvania to draw your forces in that direction, then suddenly move on Washington with the forces south of the Potomac and those he may cross over.

Again, on the 14th, General Halleck telegraphed me that-

Scouts report a large force still on the Virginia side of the Potomac. If so, I fear you are exposing your left and rear.

Again, as late as the 16th, after we had the most positive evidence that Lee's entire army was in front of us, I received the following:

WAR DEPARTMENT,

September 16, 1862-12.30 p. m.

Major-General McClellan:

Yours of 7 a. m. is this moment received. As you give me no information in regard to the position of your forces, except that at Sharpsburg, of course I cannot advise. I think, however, you will find that the whole force of the enemy in your front has crossed the river. I fear now more than ever that they will recross at Harper's Ferry or below, and turn your left, thus cutting you off from Washington. This has appeared to me to be a part of their plan, and hence my anxiety on the subject. A heavy rain might prevent it.

H. W. HALLECK,

General-in-Chief.

The importance of moving with all due caution so as not to uncover the National Capital until the enemy's position and plans were developed was, I believe, fully appreciated by me, and as my troops extended from the Baltimore and Ohio Railroad to the Potomac, with the extreme left flank moving along that stream, and with strong pickets left in rear to watch and guard all the available fords, I did not regard my left or rears as in any degree exposed. But it appears from the foregoing telegrams that the General-in-Chief was of a different opinion, and that my movements were, in his judgment, too precipitate, not only for the safety of Washington but also for the security of my left and rear.

The precise nature of these daily injunctions against a precipitate advance may now be perceived. The General-in-Chief, in his testimony before the Committee on the Conduct of the War, says:

In respect to General McClellan going too fast or too slow from Washington, there can be found no such telegram from me to him. He had mistaken the meaning of the telegrams I sent him. I telegraphed him that he was going too far, not from Washington, but from the Potomac, leaving General Lee the opportunity to come down the Potomac and get between him and Washington. I thought General McClellan should keep more on the Potomac, and press forward his left rather than his right, so as the more readily to relieve Harper's Ferry.

As I can find no telegram from the General-in-Chief recommending me to keep my left flank nearer the Potomac, I am compelled to believe that when he gave this testimony he head forgotten the purport of the telegrams above quoted, and had also ceased to remember the fact, well