Instructions, in conformity with the above, were also forwarded to the Commanders of the other Corps; and a communication of these arrangements was despatched to General MÜFFLING, with an explanation that the fatigue of the troops could not possibly admit of earlier support. This General was, at the same time, requested to forward timely intelligence of the attack upon the Duke, and of the nature of that attack, that measures might be adopted accordingly. * * * * * At five o'clock on the morning of the 18th, PAJOL started from Mazy, with SOULT's Cavalry Division and TESTE's Infantry Division, marching by St Denis and Grand Lez, to Tourinnes; where he was to await further Orders. At about eight o'clock, EXCELMANS' Corps of Heavy Cavalry, consisting of eight Regiments of Dragoons, was put in motion; and at nine o'clock, VANDAMME's and GÉRARD's Infantry Corps began their march along one and the same road, by Sart à Wallain, upon Wavre. The Left of this Column was protected, towards the Dyle, by the advance of MAURIN's Division of Light Cavalry, under General VALLIN. It was about half past ten o'clock, when EXCELMANS' Advanced Guard came up with the Prussian Rear Guard, on the road to Wavre. He immediately formed his troops in position, resting their Left upon the wooded ravine near the Farm of La Plaquerie, and their Right in the direction of Neuf Sart. While his Skirmishers were engaged with those of the Enemy, he sent the _Chef d'Escadron_ D'ESTOURMEL, to inform Marshal GROUCHY of what was going on in front, and also to make known to him that the Prussian Army had continued its retreat upon Wavre during a part of the night and that morning, for the purpose of forming a closer communication with the Duke of WELLINGTON's forces. The march of the Third and Fourth Corps was greatly retarded by the bad state of the roads, and frequent halts were occasioned by the narrowness and miry nature of the Defiles. GÉRARD, having preceded the Column, reached Sart à Wallain at eleven o'clock, where he found GROUCHY breakfasting in the house of M. HOLLAËRT, a Notary. In about half an hour after his arrival, Colonel SIMON LORIÈRE, who was acting as his Chief of the Staff, suddenly heard, while walking in the garden of the house, a distant but violent cannonade, of which he immediately went to apprise his General. GROUCHY repaired at once to the garden, accompanied by GÉRARD, VANDAMME, EXCELMANS, and several other Officers. He immediately called for M. HOLLAËRT, and asked him in what part of the country he considered this tremendous cannonade to be going on. The latter, pointing to the Forest of Soignies, replied that it must be in the direction of Planchenoit, Mont St Jean, and that vicinity.