CHAPTER XXIX.
THE TRUCE OF GOD.
BY the 30th of July the work in the caverns was so far advanced that the Council was able to authorise the departure of Alan and his companions for the outside world. The great vertical sluice-door, a huge sheet of steel forty feet long, twenty wide, and eighteen inches thick, and footed with a great indiarubber pad, was in its place, suspended at the top of the steel-lined grooves, which had been sunk three feet into each of the rock walls of the chasm into which the water-tunnel from the lake opened.
On the morning of the 30th it was sent down into its final position. The momentous experiment proved completely successful. The huge mass of metal descended slowly over the mouth of the tunnel into the black, swift stream at the bottom of the chasm. As its enormous weight crushed the indiarubber pad down into all the inequalities of the floor the outrush of the waters instantly stopped, and the channel ran dry save for the fierce jets of water which spouted out over the top of the plate.
The crevices through which these came were easily plugged, and when this was done it was found that the waters of the lake were rising at the rate of three feet an hour. This proved that, whether the lake had another outlet or not, the damming of the subterranean channels would be quite sufficient to flood the whole valley.
The gate was then raised again, and the waters permitted to flow as before. The triple doors at the entrance to the cavern were already in position when this was done, as the task of placing them had necessarily been much easier than the construction of the water-gate. Nothing but details now remained to be completed, and there was therefore no reason for any further postponement of Alan’s mission.
Alexis had also succeeded in carrying his point, and getting permission to accompany Alan in the Isma. He had had no difficulty in satisfying the Council that the risk would be enormously diminished by sending two air-ships instead of one, for while Alan descended to the earth to convey his message to a hostile city, he would be able to remain in the air, dominating it with his guns, and ready to lay it in ruins if the flag of truce were not respected.