That it continued outside he guessed by a slight but distinct feeling of pressure in the air, showing that the column of water outside was compressing it.  He had no fear of any bad consequences from this source, as even a height of twelve feet of water outside would not give any unbearable pressure.  He was more afraid that he himself would exhaust the air, but he believed that there would be sufficient; and as he knew that the less he exerted himself the less air he required, he floated quietly on his back, with his feet resting on the bar across the loophole, now two feet under water.

He scarcely felt the water cold.  The rain had come from a warm quarter; and the temperature of the water was actually higher than that of the cold and humid dungeon.

Hour after hour passed.  The night appeared interminable.  From time to time Rupert dived so as to look through the loophole, and at last was rewarded by seeing a faint dull light.  Day was beginning; and Rupert had no doubt that with early morning the sluices would be opened, and the moat entirely cleared of water.

He had, when talking with his gaoler one day, asked him how they got rid of the water in the dungeon after a flood, and the man said that there were pipes from the floor of each dungeon into the moat.  At ordinary times these pipes were closed by wooden plugs, as the water outside was far above the floor; but that after a flood the water was entirely let out of the moat, and the plugs removed from the pipes, which thus emptied the dungeons.

From the way in which the fellow described the various arrangements, Rupert had little doubt that the sluice gates were at times purposely left closed, in order to clear off troublesome prisoners who might otherwise have remained a care and expense to the state for years to come.

Long as the night had seemed, it seemed even longer before Rupert felt that the water was sinking.  He knew that after the upper sluice had opened the fosse might take some time to fall to the level of the water inside the dungeon, and that until it did the water inside would remain stationary.

He passed the hours by changing his position as much as possible; sometimes he swam round and round, at other times he trod water, then he would float quietly, then cling to the bar of the loophole.

The descent of the water came upon him at last as a surprise.  He was swimming round and round, and had not for some time touched the wall, when suddenly a ray of light flashed in his face.  He gave a cry of joy.  The water had fallen below the top of the loophole, and swimming up to it, he could see across the fosse, and watch the sunlight sparkling on the water.  It was two months since he had seen the light, and the feeling of joy overpowered him more than the danger he had faced.

Rapidly the water fell, until it was level with the bottom of the loophole.  Then hours passed away; for the fosse would have to be emptied before the drain leading from the dungeon could be opened.  However, Rupert hardly felt the time long.  With his hands on the bar and in the loophole, he remained gazing out at the sunlight.