Early on the morning of the 15th, these troops were lying quietly in their cantonments, perfectly unconscious of the advance of the French Army, when they heard a brisk cannonade at a distance in the direction of Charleroi; but not having received the slightest intimation of the Enemy's approach, they concluded that the firing proceeded from the Prussian Artillery practice, which they had frequently heard before, and to which they had therefore become accustomed. Gradually towards noon, however, the cannonade became more distinctly audible; and, in the afternoon, the arrival of a wounded Prussian soldier completely set at rest all doubt as to the advance of the French. An Orderly was immediately despatched with the intelligence to the Regimental Head Quarters, whence it was also communicated to General DE PERPONCHER's Head Quarters at Nivelles. In the meantime, Major NORMANN, who commanded the 2nd Battalion of the 2nd Regiment of Nassau, drew up the latter with the Battery in position in rear of Frasne, and upon the road to Quatre Bras, after having posted a Picquet of observation in advance of the village. PERPONCHER lost not a moment in ordering both Brigades of his Division to hasten towards their respective points of assembly; the 1st Brigade, under General BYLANDT, to Nivelles, and the 2nd, under Colonel GÖDECKE, to Quatre Bras. Before this Order, however, could possibly reach these troops, Prince BERNHARD of Saxe Weimar, who commanded the Regiment of Orange-Nassau, at Genappe, having been informed by the Officer of the Dutch-Belgian _Maréchaussées_, who had been compelled to quit his post at Charleroi, that the French were advancing from that place, took upon himself to move forward with the above Regiment from Genappe to Quatre Bras, and despatched a report of such movement to the Head Quarters of the Brigade at Hautain le Val, as also, subsequently, to General DE PERPONCHER at Nivelles, by Captain GAGERN, of the Dutch-Belgian Staff, who happened to be just then at Genappe, for the purpose of collecting information. About six o'clock in the evening, parties of Lancers belonging to PIRÉ's Light Cavalry Division of REILLE's Corps appeared in front of Frasne, and soon drove in Major NORMANN's Picquet.