'It is a noisy thing,' he said, as they stood before it, 'but when I make another, it shall do its work that thou wouldst not hear it outside the door. Now listen to me for a moment, cousin. Should it come to a siege and I not at Raglan--the wise man will always provide for the worst--Caspar will be wanted everywhere. Now this engine is essential to the health and comfort, if not to the absolute life of the castle, and there is no one at present capable of managing it save us two. A very little instruction, however, would enable any one to do so: will you undertake it, cousin, in case of need?' 'Make me assured that I can, and I will, my lord,' answered Dorothy. 'A good and sufficing answer,' returned his lordship, with a smile of satisfaction. 'First then,' he went on, 'I will show you wherein lies its necessity to the good of the castle. Come with me, cousin Dorothy.' He led the way from the room, and began to ascend the stair which rose just outside it. Dorothy followed, winding up through the thickness of the wall. And now she could not hear the engine. As she went up, however, certain sounds of it came again, and grew louder till they seemed close to her ears, then gradually died away and once more ceased. But ever, as they ascended, the rushing sound which had seemed connected with it, although so distant, drew nearer and nearer, until, having surmounted three of the five lofty stories of the building, they could scarcely hear each other speak for the roar of water, falling in intermittent jets. At last they came out on the top of the wall, with nothing between them and the moat below but the battlemented parapet, and behold! the mighty tower was roofed with water: a little tarn filled all the space within the surrounding walk. It undulated in the moonlight like a subsiding storm, and beat the encircling banks. For into its depths shot rather than poured a great volume of water from a huge orifice in the wall, and the roar and the rush were tremendous. It was like the birth of a river, bounding at once from its mountain rock, and the sound of its fall indicated the great depth of the water into which it plunged. Solid indeed must be the walls that sustained the outpush of such a weight of water! 'You see now, cousin, what yon fire-souled slave below is labouring at,' said his lordship. 'His task is to fill this cistern, and that he can in a few hours; and yet, such a slave is he, a child who understands his fetters and the joints of his bones can guide him at will.' 'But, my lord,' questioned Dorothy, 'is there not water here to supply the castle for months? And there is the draw-well in the pitched court besides.'