General Wilcox was on the road leading from the bridge to Sharpsburg, which passes up a ravine. A brook which has its rise beyond the town, gurgles by the roadside. Rebel batteries on the hills in front of the town enfiladed the ravine, sweeping it from the town to the river. There was no shelter for the troops while advancing. They must take the storm in their faces. Neither was there any cover for Rodman, Sturgis, and Scammon. The ground, from the stone wall on the top of the river bank to the hills occupied by Hill and Longstreet, was all tillage land,--wheat-fields, and pastures, and patches of corn. There were fences to throw down, hills to climb, all to be done under fire from cannon arranged in crescent form, pouring down a concentrated fire from the heights. The signal officer, upon Elk Ridge, five hundred feet above the battle-field, beholds all the operations of the Rebel army. From his lookout, with his telescope, he can sweep the entire field. His assistant waves a flag, and an officer, with his eye at the telescope by McClellan's head-quarters, reads a message of this import, transmitted by the little flag. "The Rebels are weakening their left, and concentrating their troops upon their right." The officer writes it in his message book, tears out the leaf, and hands it to General McClellan. He thus knows Lee's movements, the disposition of his forces, as well as if he himself had looked from the mountain summit upon the moving column. He can make a counter movement, if he chooses, by weakening his own right to help Burnside, or he can throw in Porter's corps of twelve thousand strong, to help Burnside, by a dash upon the center, or leave Burnside to struggle against the superior force in front of him, move Porter upon the double quick to the right, unite him with Franklin, order up fifty or eighty guns from his reserve artillery, gather the brigades of Hooker's, Williams's, and Sumner's corps to hold the line, while Franklin and Porter, twenty thousand strong, fall like a thunderbolt upon Jackson, and break him in pieces. He can adopt one other plan,--hold what has already been gained. He adopts the last, and makes no movement. It was three o'clock before Burnside's troops were in position for the advance. The entire line moved, Wilcox and Crook up the ravine and on both sides of it, Rodman across the fields south of the highway, and Scammon along the river bank. A. P. Hill, from his position, enfiladed Rodman, who was obliged to change his line of march. He severed his right from Wilcox, and wheeled towards the southwest. He was obliged to make this maneuver, to meet Hill face to face, but it brought upon his line an enfilading fire from the cannon and infantry nearer the town, and it opened a wide gap in the line, which Burnside was obliged to fill by pushing in Sturgis,--his only reserve.