to the city.  The mirages blurred and distorted the picture, so that some of the routed Arabs walked in air and some through water, and all were misty and unreal.  But the sight was sufficient to excite the fiercest instincts of cavalry.  Only the scattered parties in the plain appeared to prevent a glorious pursuit.  The signalling officer was set to heliograph back to the Sirdar that the ridge was unoccupied and that several thousand Dervishes could be seen flying into Omdurman.  Pending the answer, we waited; and looking back northwards, across the front of the zeriba, where the first attack had been stopped, perceived a greyish-white smudge, perhaps a mile long.  The glass disclosed details—­hundreds of tiny white figures heaped or scattered; dozens hopping, crawling, staggering away; a few horses standing stolidly among the corpses; a few unwounded men dragging off their comrades.  The skirmishers among the rocks of Surgham soon began to fire at the regiment, and we sheltered among the mounds of sand, while a couple of troops replied with their carbines.  Then the heliograph in the zeriba began to talk in flashes of light that opened and shut capriciously.  The actual order is important.  ‘Advance,’ said the helio, ’and clear the left flank, and use every effort to prevent the enemy re-entering Omdurman.’  That was all, but it was sufficient.  In the distance the enemy could be seen re-entering Omdurman in hundreds.  There was no room for doubt.  They must be stopped, and incidentally these small parties in the plain might be brushed away.  We remounted; the ground looked smooth and unbroken; yet it was desirable to reconnoitre.  Two patrols were sent out.  The small parties of Dervishes who were scattered all over the plain and the slopes of the hill prevented anything less than a squadron moving, except at their peril.  The first patrol struck out towards Omdurman, and began to push in between the scattered Dervishes, who fired their rifles and showed great excitement.  The other patrol, under Lieutenant Grenfell, were sent to see what the ground looked like from further along the ridge and on the lower slopes of Surgham.  The riflemen among the rocks turned their fire from the regiment to these nearer objects.  The five brown figures cantered over the rough ground, presenting difficult targets, but under continual fire, and disappeared round the spur.  However, in two or three minutes they re-appeared, the riflemen on the hill making a regular rattle of musketry, amid which the Lancers galloped safely back, followed last of all by their officer.  He said that the plain looked as safe from the other side of the hill as from where we were.  At this moment the other patrol returned.  They, too, had had good fortune in their adventurous ride.  Their information was exact.  They reported that in a shallow and apparently practicable khor about three-quarters of a mile to the south-west, and between the regiment and the fugitives, there was drawn up a formed body of Dervishes about 1,000 strong.  Colonel Martin decided on this information to advance and attack this force, which alone interposed between him and the Arab line of retreat.  Then we started.