Nobody had thought of that obvious plan. Like most great inventions it was simple--when seen. Thereafter one or two men always sat at the end of the tunnel fanning air into it with their hats. But even so, many a candle went out and many a digger was pulled out, black in the face and almost dead. The tunnel sloped downwards, of course, to reach the sewer. It sloped too far down. It got below the water-level of the canal. Hamilton was caught in it by the rush of water and almost drowned. So much work had to be done over again. Then came a crushing blow. When the small sewer was finally reached, it proved to be too small for a man to pass through it. But it had a wooden lining, which was bit by bit taken off. When this had been done to within a few feet of the main sewer, two men were detailed to cut their way through. The next night was set as the time for the escape. None of the thirteen slept while the two were cutting away the final obstacle. The thirteen did not sleep the next night either, for it was 36 hours before the two came back with their heartbreaking news. They had found the last few feet of the sewer-lining made of seasoned oak, three inches thick and hard as stone. The poor old knife that had served them so long and so well, could not even scratch the toughened oak. Thirty-nine nights of grinding toil had ended in failure. Meanwhile the thirteen had had to face a new problem. There were two roll-calls every day, at 9 A.M. and 4 P.M. How were the two absent men to answer? At roll-call everybody stood in one long line and everybody was counted. If the count were two short, there would be swift search for the missing. And the beginning of the tunnel was hidden only by a few bundles of straw. This was before they knew the tunnel was useless, but had they known it they would have been scarcely less anxious, for its discovery would have made all future attempts to escape more dangerous and more doubtful. However, the roll-call problem was safely solved. The thirteen crowded into the upper end of the line and two of them, as soon as they had answered to their own names, dropped back, crouched down, crept behind the backs of many men to the other end of the line, slipped into place, and there answered for the missing men, without detection. In the afternoon, they came very near being caught. Some of the other prisoners thought this was being done just for fun, to confuse the Confederate clerk who called the roll, and thought they would take a hand in the fun too. There was so much dodging and double answering that "Little Ross," the good-humored little clerk, lost his temper and ordered the captives to stand in squads of ten to be counted. By this time he had called the roll half a dozen times, with results varying from minus one to plus fifteen. When he gave his order, an order obedience to which would have certainly told the tale of two absentees, he went on to explain why he gave it.