The weather, during the morning, had become oppressively hot; it was now a dead calm; not a leaf was stirring; and the atmosphere was close to an intolerable degree; while a dark, heavy, dense cloud impended over the combatants. The 18th Hussars were fully prepared, and awaited but the command to charge, when the Brigade guns on the right commenced firing, for the purpose of previously disturbing and breaking the order of the Enemy's advance. The concussion seemed instantly to rebound through the still atmosphere, and communicate, as an electric spark, with the heavily charged mass above. A most awfully loud thunder clap burst forth, immediately succeeded by a rain which has never, probably, been exceeded in violence even within the tropics. In a very few minutes the ground became perfectly saturated; so much so that it was quite impracticable for any rapid movement of the Cavalry. The Enemy's Lancers, opposed to the Sixth British Brigade, began to relax in their advance, and to limit it to skirmishing; but they seemed more intent upon endeavouring to envelope, and intercept the retreat of, the Hussars. VIVIAN now replaced the 18th Hussars by the 1st Hussars of the King's German Legion, as Rear Guard, with Orders to cover well the Left Flank and Left Front of the Brigade. He had already sent off his Battery of Horse Artillery, to cross the Genappe by the Bridge of Thuy, and despatched an Aide de Camp to VANDELEUR, to request he would move his Brigade as quickly as possible across that Bridge, so that he might meet with no interruption in his retreat, in the event of his being hard pressed. Of the Centre Column, the Heavy Brigades of Lord EDWARD SOMERSET and Sir WILLIAM PONSONBY had retired along the Charleroi road, and were taking up a position on some high ground, a little in rear of Genappe, on either side of that road. The detached Squadron of the 11th Light Dragoons (under Captain SCHREIBER), was withdrawn and directed to retire through the above town. The 23rd Light Dragoons were also withdrawn, and posted upon the ascent between Genappe and the position occupied by the two Heavy Brigades. The 7th Hussars continued on the south side of Genappe, as Rear Guard. Neither the Centre, nor the Right, Column experienced any serious molestation in its retreat while on the French side of the Genappe: large bodies of Cavalry were seen in motion, but their Advanced Guards limited their attacks to skirmishing.