Captain Ayer, who has seen fighting in Mexico, brings his guns upon the hill, wheels them into position, and sights them towards the breastworks. There is a flash, a puff of smoke, a screaming in the air, and then across the stream a handful of cloud bursts into view above the Rebel lines. The shell has exploded. There is a sudden movement of the Rebel troops. It is the first gun of the morning. And now, two miles down the Run, by Mitchell's Ford, rolling, echoing, and reverberating through the forests, are other thunderings. General Richardson has been waiting impatiently to hear the signal gun. He is to make a feint of attacking. His cannonade is to begin furiously. He has six guns, and all of them are in position, throwing solid shot and shells into the wood where Longstreet's men are lying. All of Ayer's guns are in play, hurling rifled shot and shells, which scream like an unseen demon as they fly over the cornfield, over the meadow lands, to the woods and fields beyond the stream. General Hunter and General Heintzelman, with their divisions, have left the turnpike two miles from Centreville, at Cub Run bridge, a rickety, wooden structure, which creaks and trembles as the heavy cannon rumble over. They march into the northwest, along a narrow road,--a round-about way to Sudley Springs. It is a long march. They started at two o'clock, and have had no breakfast. They waited three hours at Cub Run, while General Tyler's division was crossing, and they are therefore three hours behind the appointed time. General McDowell calculated and intended to have them at Sudley Springs by six o'clock, but now it is nine. They stop a half-hour at the river-crossing to fill their canteens from the gurgling stream. Looking south from the little stone church, you see clouds of dust floating over the forest-trees. The Rebels have discovered the movement, and are marching in hot haste to resist the impending attack. General Evans has left a portion of his command at Stone Bridge, and is hastening with the remainder to the second ridge of land north of the turnpike. He plants his artillery on the hill, and secretes his infantry in a thicket of pines. General Bee is on the march, so is General Bartow and General Jackson, all upon the double-quick. Rebel officers ride furiously, and shout their orders. The artillerymen lash their horses to a run. The infantry are also upon the run, sweating and panting in the hot sunshine. The noise and confusion increase. The booming deepens along the valley, for still farther down, by Blackburn's Ford, Hunt's battery is pouring its fire upon Longstreet's, Jones's, and Ewell's men. The Union troops at Sudley Springs move across the stream. General Burnside's brigade is in advance. The Second Rhode Island infantry is thrown out, deployed as skirmishers. The men are five paces apart. They move slowly, cautiously, and nervously through the fields and thickets.