There is in the letter no trace of that certainty as to the position of affairs so plainly exhibited in the verbal orders. The news that a Prussian corps has been seen at Gembloux has evidently made a strong impression on the Emperor. It may very possibly indicate that Blücher is not falling back to Namur. The statement is twice made in the letter that the Emperor is in doubt as to the intentions of the Prussians, and the chief task now imposed upon Grouchy is to ascertain those intentions. _The precise danger to be anticipated is stated explicitly._ Grouchy is warned in so many words that the Prussians may be intending to unite with the English to try the fate of another battle for the defence of Brussels,—which was exactly what they were intending to do, and what they succeeded in doing. Whether they are or are not intending to do this, is the principal thing for Grouchy to find out. As the Emperor had previously informed Grouchy of his determination to fight the English “if they will stand on this side of the Forest of Soignes,”—which meant of course that he looked upon a battle with them the next day as very possible,—this question of the Prussians uniting with the English in fighting this battle was of vital importance to him.[479] _What Grouchy was to do if he found the Prussians directing their movements so as to compass this end, it was left to him to determine for himself._ It might be that he could hinder the accomplishment of their design most effectually by attacking them; it might be that his best course would be to rejoin the main army as soon as he could, or to manœuvre so as to act in conjunction with it. It was impossible for Napoleon to tell beforehand how things would turn out. Full discretion was therefore left to Grouchy to take whatever course might seem best to him. Marshal Grouchy was making his arrangements to get his command under way when he received this letter. He experienced great delay in beginning his march to Gembloux. Vandamme did not get started till two o’clock. Gérard left Ligny an hour later. It came on to rain hard about two o’clock, and the roads soon became very bad. Grouchy did not succeed in getting farther with his two infantry corps that night than Gembloux, which is rather less than eight miles from St. Amand.[480] The cavalry of Exelmans was, however, stationed at Sauvenières, to gather information. Grouchy had with him a force of 33,319 men of all arms, of whom 4,446 were the cavalry belonging to the two corps of Pajol and Exelmans.[481] Napoleon took with himself Domon’s light cavalry division of the 3d Corps, but Grouchy retained that of Maurin, belonging to the 4th Corps,—say, 1,500 men. That is, he had 6,000 cavalry in all.