At length, about half past nine o'clock, Prince BLÜCHER's Aide de Camp, Major WEYRACH, arrived at BÜLOW's Head Quarters, and brought the Orders for the retreat of the Fourth Corps to Dion le Mont, near Wavre, by Walhain and Corbaix. The Orders also required that BÜLOW should post the main body of his Rear Guard (which consisted of the Fourteenth Brigade) at Vieux Sart; as also that he should send a Detachment, consisting of one Regiment of Cavalry, two Battalions of Infantry, and two guns of Horse Artillery, to the Defile of Mont St Guibert, to act, in the first instance as a Support to Lieutenant Colonel SOHR, who was at Tilly, and then, upon the latter falling back, to act as Rear Guard in this direction. Lieutenant Colonel LEDEBUR was accordingly detached upon this duty with the 10th Hussars, the Fusilier Battalions of the 11th Regiment of Infantry and 1st Regiment of Pomeranian Landwehr, together with two guns from the Horse Battery No. 12. The Corps itself moved directly upon Dion le Mont, and on reaching the Height near that town, on which is situated the public house of _A tous vents_, took up a position close to the intersection of the roads leading to Louvain, Wavre, and Gembloux. * * * * * At two o'clock in the afternoon, THIELEMANN commenced his march upon Wavre; where the Corps arrived late in the evening, and took up its position at La Bavette, leaving the Ninth Infantry Brigade (General BORCKE) and the Cavalry Brigade of Colonel Count LOTTUM, on the right bank of the Dyle. In this position the Corps was now rejoined by Colonel MARWITZ' Cavalry Brigade, which had retired by Tilly; as also by the 2nd Battalion of the 3rd Kurmark Landwehr, and the two Squadrons of the 6th Kurmark Landwehr Cavalry, which troops had been left at Dinant. The Squadron of the 7th Uhlans that had been detached to Onoz, also joined, but having fallen in with a superior force of the Enemy's Cavalry, had experienced a great loss. The two Squadrons of the 9th Hussars, belonging to this Corps, had not yet arrived from Ciney. * * * * * The Prussian Head Quarters were established, early on the 17th, at Wavre. The veteran Field Marshal, who was still suffering considerably in consequence of his fall, was obliged to seek rest the moment he arrived there, and did not quit his bed during the remainder of the day.