The Centaur by Algernon Blackwood

But O'Malley did not immediately return to his own cabin; he yielded to Dr. Stahl's persuasion and dropped into the armchair he had already occupied more than once, watching his companion's preparations with the lamp and coffeepot.

With his eyes, that is, he watched, staring, as men say, absent-mindedly; for the fact was, only a little bit of him hovered there about his weary physical frame. The rest of him was off somewhere else across the threshold subliminal: below, with the Russian, beyond with the traveling spirit of the boy; but the major portion, out deep in space, reclaimed by the Earth.