That NAPOLEON should have neglected to follow up the advantages which fortune had thrown in his way on the morning of the 17th of June, is quite incomprehensible. With the exception of a Prussian Picquet at Gentinnes, his whole front as far as Gembloux, was perfectly clear of an Enemy. WELLINGTON was still in position at Quatre Bras, where his Left had become exposed by the retreat of the Prussians, and in rear of which point was the Defile of Genappe. There was nothing to prevent NAPOLEON from marching directly upon that Defile; and supporting, by a vigorous attack upon the Anglo-Allied Left and Rear, a simultaneous movement against the Front by the force under NEY. Whither had fled the mighty spirit which had shone forth with such dazzling brilliancy in former Wars, and which had never displayed the energy of its powers of combination, and activity in following up successes, more eminently than in the Campaign of the previous year? When before did he omit pressing every advantage to the utmost, or neglect to seize that moment of time, in which, having defeated one portion of his Enemies, he was enabled to fall with combined force upon another? His Army was not more fatigued than was that of WELLINGTON, which had arrived at Quatre Bras by forced marches. The troops which he subsequently did lead upon that point, when it was too late, consisting chiefly of the Imperial Guard and the Sixth Corps, were comparatively fresh. The former had not been engaged at Ligny until towards the termination of the action, when they suffered scarcely any loss; the latter, which arrived later, had remained intact. The idea of forming a junction with NEY, with a view of attacking WELLINGTON, was certainly entertained; but its execution was most unaccountably and unnecessarily delayed until its intended effect could not but fall powerless upon a vigilant Enemy, fully prepared, by having improved the precious moments of time, thus lost, to detect the purpose of the movement, and to ward off the intended blow.