He had noticed across the skylight a head in a grey cap.

But when, after a time, he crossed over to the other side of the deck he discovered that it was not the captain's head at all.

He became aware of grey hairs curling over the nape of the neck.

How could he have made that mistake?
But on board ship away from the land one does not expect to come upon a stranger.
Powell walked past the man.

A thin, somewhat sunken face, with a tightly closed mouth, stared at the distant French coast, vague like a suggestion of solid darkness, lying abeam beyond the evening light reflected from the level waters, themselves growing more sombre than the sky; a stare, across which Powell had to pass and did pass with a quick side glance, noting its immovable stillness.