Yet Jack was mistaken in so supposing, for as the time went on he became aware of certain sounds out there on the plain which seemed to indicate pretty unmistakably that, despite the darkness, the Spaniards were busily employed. When the moaning and sighing of the night wind among the branches of the trees, the rustle of the bamboos, and the clash of the palm leaves subsided for an instant, allowing more distant sounds to reach his ears, he intermittently caught what seemed to be the sounds of picks and shovels at work at no very great distance; moreover, there were lights flitting about the distant camp, and much movement there, though what it portended Jack was quite unable to discover, even with the help of his night glasses. At length, however, the period of darkness came to an end, for sheet lightning began to flicker and quiver among the densely packed clouds low down on the western horizon, at first for an instant only and at comparatively long intervals, but soon increasing greatly in vividness and rapidity: and then the young Englishman perceived, to his disgust and alarm, that the Spanish soldiers had availed themselves of the obscurity not only to entrench a strong body of riflemen to right and left of their own end of the ruined bridge, but also to advance a long, light platform, or gangway, mounted on the wheels of one of the disabled field pieces, which they seemed to be preparing to throw across the gap in the bridge as soon as they could get sufficient light to enable them to run it into position; indeed, they were actually engaged in moving it forward at the very moment when Jack discovered its existence.