He had been there so long, and he was so much absorbed in what was passing before his eyes that he had not noted the great change in the nature of the night.

Moon and stars were gone.

Heavy clouds were sailing low.

Thunder muttered on the western horizon, and there were flashes of distant lightning.
Hope sprang up in Robert's heart.

Perhaps the fear of a storm would drive them to the shelter of the ship, but they did not stir.