J. H. VAN ALEN, Brigadier-General and Aide-de-Camp. (Copy sent Gen. Sedgwick ten P.M.) At eleven P.M., when this order of ten o'clock was received, Sedgwick had his troops placed, and his dispositions taken, to carry out the orders to pursue, on the Bowling-Green road, an enemy indicated to him as in rapid retreat from Hooker's front; and was actually in bivouac along that road, while a strong picket-line was still engaged skirmishing with the force in his front. By this time the vanguard of his columns had proceeded a distance variously given as from one to three miles below the bridges in this direction; probably near the Bernard House, not much beyond Deep Creek. It is to be presumed that the aide who bore the despatch, and reached Sedgwick later than the telegram, gave some verbal explanation of this sudden change of Hooker's purpose; but the order itself was of a nature to excite considerable surprise, if not to create a feeling of uncertainty. Sedgwick changed his dispositions as speedily as possible, and sent out his orders to his subordinates within fifteen minutes after receipt of Hooker's despatch; but it was considerably after midnight before he could actually get his command faced about, and start the new head of column toward Fredericksburg. Knowing the town to be occupied by the Confederates, Sedgwick was obliged to proceed with reasonable caution the five or six miles which separated his command from Fredericksburg. And the enemy appears to have been sufficiently on the alert to take immediate measures to check his progress as effectually as it could with the troops at hand. Fredericksburg and the heights beyond were held by Early's division and Barksdale's brigade, with an adequate supply of artillery,--in all some eighty-five hundred men. Sedgwick speaks, in his testimony before the Committee on the Conduct of the War, as if he understood at this time that Early controlled a force as large as his own; but he had been advised by Butterfield that the force was judged to be much smaller than it actually was. In his report, Early does not mention Sedgwick's advance on the Bowling-Green road, nor is it probable that Sedgwick had done more than to advance a strong skirmish-line beyond his column in that direction. Early's line lay, in fact, upon the heights back of the road, his right at Hamilton's Crossing, and with no considerable force on the road itself. So that Sedgwick's advance was skirmishing with scouting-parties, sent out to impede his march.