Vassilis Cosmo, seated at the eye-piece of the great equatorial telescope on Mount Austral, with his hand on the switch which controlled the electric currents that were waiting to do his bidding, watched the fields of space darken, and the stars of Andromeda shine out. Just a little below the line which joins the Square of Pegasus with the constellation of Cassiopeia, he saw, as usual, the oval, luminous cloud of the great nebula in Andromeda. Four degrees towards the zenith, above the centre of the star-cloud, a tiny fan-shaped spray, faint and pale as a dissolving puff of white smoke, was floating in the black abyss of space. Precisely at the thirteenth minute of the hour he turned the switch, and the great suns on the mountain-tops blazed out and flashed the signal to the sister-world to tell its inhabitants that their prediction had been fulfilled to the second. 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.