this part of our line with the utmost vigilance, lest the enemy should take advantage of the first exhibition of weakness here to push upon us a vigorous assault for the purpose of piercing our center and turning our rear, as well as to capture or destroy our supply trains. Once having penetrated this line, the enemy's passage to our rear could have met with but rabble resistance, as there were no reserves to re-enforce or close up the gap.

Toward the middle of the afternoon, proceeding to the right, I found that Sumner's, Hooker's, and Mansfield's corps had met with serious losses. Several general officers had been carried from the field severely wounded, and the aspect of affairs was anything but promising. At the risk of greatly exposing our center, I ordered two brigades from Porter's corps, the only available troops, to re-enforce the right. Six battalions of Syke's Regulars had been thrown forward across the Antietam Bridge on the main road to attack and drive back the enemy's sharpshooters, who were annoying Pleasonton's horse batteries in advance of the bridge. Warren's brigade, of Porter's corps, was detached to hold a position on Burnside's right and rear, so that Porter was left at one time with only a portion of Sykes' division and one small brigade of Morell's division (but little over 3,000 men) to hold his important position.

General Sumner expressed the most decided opinion against another attempt during that day to assault the enemy's position in front, as portions of our troops were so much scattered and demoralized. In view of these circumstances, after making changes in the position of some of the troops, I directed the different commanders to hold their positions, and, being satisfied that this could be done without the assistance of the two brigades from the center, I countermanded the order, which was in course of execution.

General Slocum's division replaced a portion of General Sumner's troops, and positions were selected for batteries in front of the woods. The enemy opened several heavy fires of artillery on the position of our troops after this, but our batteries soon silenced them.

On the morning of the 17th, General Pleasonton, with his cavalry division and the horse batteries, under Captains Robertson, Tidball, and Lieutenant Hains, of the Second Artillery, and Captain Gibson, Third Artillery, was ordered to advance on the turnpike toward Sharpsburg, across Bridge Numbers 2, and support the left of General Sumner's line. The bridge being covered by a fire of artillery and sharpshooters, cavalry skirmishers were thrown out, and Captain Tidball's battery advanced by piece and drove off the sharpshooters, with canister, sufficiently to establish the batteries above mentioned, which opened on the enemy with effect. The firing was kept up for about two hours, when, the enemy's fire slackening, the batteries were relieved by Randol's and Van Reed's batteries, U. S. Artillery. About 3 o'clock, Tidball, Robertson, and Hains returned to their positions on the west of Antietam, Captain Gibson having been placed in position on the east side to guard the approaches to the bridge. These batteries did good service, concentrating their fire on the column of the enemy about to attack General Hancock's position, and compelling it to find shelter behind the hills in rear.

General Sykes' division had been in position since the 15th, exposed to the enemy's artillery and sharpshooters. General Morell had come up on the 16th, and relieved General Richardson, on the right of General Sykes. Continually under the vigilant watch of the enemy, this corps guarded a vital point.