An hour after midnight
He meant now to follow Sherburne 's force , see what plan it would attempt , what point , perhaps , it would select for the bridge , and then bring the Union brigades in haste to defeat it . It is said that men often feel when they are watched , although the watcher is invisible , but it was not so in Sherburne 's case . He did not in the least suspect the presence of Shepard or of any foe , and the spy , after he had seen all he wished , withdrew , with the same stealth that had marked his coming . An hour after midnight all were awakened and they rode away . The next day they reached the Potomac near Williamsport , where their pontoon bridge had been destroyed , and looked upon the wide stream of the Potomac , far too deep for fording . `` If General Lee is attacked on the banks of this river by greatly superior forces , '' said Sherburne , `` he 'll have no time to build bridges . If we did n't happen to be victorious our forces would have to scatter into the mountains , where they could be hunted down , man by man . ''