As Napoleon’s fate was to depend largely on an intelligent carrying out of this order, we may point out that it consisted of two chief parts, the general aim and the means of carrying out that aim.  The aim was to find out the direction of the Prussians’ retreat, and to prevent them joining Wellington, whether for the defence of Brussels or of Liege.  The means were an advance to Gembloux and scouting along the Namur and Maestricht roads.  The chance that the allies might reunite for the defence of Brussels was alluded to, but no measures were prescribed as to scouting in that direction:  these were left to Grouchy’s discretion.  It must be confessed that the order was not wholly clear.  To name the towns of Brussels and Liege (which are sixty miles apart) was sufficiently distracting; and to suggest that only the eastern and south-eastern roads should be explored was certain to limit Grouchy’s immediate attention to those roads alone.  For he distrusted alike his own abilities and the power of the force placed at his disposal; and an officer thus situated is sure to inclose himself in the strict letter of his instructions.  This was what he did, with disastrous results.

Grouchy had hitherto held no important command.  As a cavalry general he had done brilliant service; but now he was launched on a duty that called for strategic insight.  His force was scarcely equal to the work.  True, it was strong for scouting, having nearly 6,000 light horse; but the 27,000 footmen of Vandamme’s and Gerard’s corps had been exhausted by the deadly strife in the villages and were expecting a day’s rest.  Their commanders also resented being placed under Grouchy.  In fact, leaders and men disliked the task, and set about it in a questioning, grumbling way.  The infantry did not start till about 3 o’clock and only reached Gembloux late that evening—­nine miles in six hours!  The cavalry, too, was so badly handled by Excelmans around Gembloux that Thielmann’s corps slipped away northward.  The rain fell in torrents, obscuring the view; but it seems strange that the direction of the Prussian retreat was not surmised until about nightfall.

Meanwhile, on the French left wing, Ney had been equally lax.  He must have received Napoleon’s order to occupy Quatre Bras, “if there was only a rearguard there,” a little before 10 a.m.; but he took no steps beyond futile skirmishing, and apparently knew not that the British were slipping away.

About 2 p.m., when the British cavalry was ready to turn rein, the Duke and Sir H. Vivian saw the glint of cuirasses along the Sombref road.  It was the vanguard of the Emperor’s advance.  Furious that his foes were escaping from his clutches, Napoleon had left his carriage and was pressing on with the foremost horsemen.  To Ney he sent an imperative summons to advance, and when that Marshal came up, greeted him with the words “You have ruined France.”  But it was time for deeds, not words; and he now put forth all his strength.  At once he flung his powerful cavalry at the British rear; and even now it might have gone hard with Wellington had not the lowering clouds burst in a deluge of rain.  Quickly the road was ploughed up; and the cornfields became impassable for the French horsemen.