They sailed on north, out into Chryse Gulf. Copernicus Island appeared over the water to their right, then Galileo Island behind it. Then both receded under the blue horizon again. The swells on the horizon were individually distinct, so that the horizon was not a straight blue line against the sky, but rather a shifting array of swell tops, one after another in swift succession. The groundswell was coming out of the north, almost directly ahead of them, so that looking to port or starboard the horizon line was particularly jagged, a wavy line of blue water against the blue sky, in a too-small circle surrounding the ship— as if the proper Terran distance to the horizon were stubbornly embedded in the brain’s optics, so that when they saw things clearly here, they would always appear to stand on a planet too small for them. Certainly there was a look of the most extreme discomfort on Ann’s face; she glared at the waves, groundswell after groundswell lifting the bow and then the stern. There was a cross chop nearly at right angles to the groundswell, pushed by the west wind and ruffling the bigger broader swells. Wavetank physics; one could see it all laid out; it reminded Sax of the physics lab on the second story of the northeasternmost building in his high school, where hours had passed like minutes, the flat little wavetank full of marvels. Here the groundswell originated in the North Sea’s perpetual eastward motion around the globe; the swell was greater or smaller depending on whether local winds reinforced it or interfered with it. The light gravity made for big broad waves, quickly generated by strong winds; if today’s wind got very much stronger, for instance, then the wind-chop from the west would quickly grow bigger than the groundswell from the north, and obscure it completely. Waves on the North Sea were notorious for their size and mutability, their recombinant surprises, though it was also true that they moved fairly slowly through the water; big slow hills, like the giant dunes of Vastitas far underneath them, migrating around the planet. Sometimes they could get very big indeed; in the aftermath of the typhoons that blew over the North Sea, waves seventy meters high had been reported.

This lively cross chop seemed enough for Ann, who was looking a bit distressed. Sax could not think what to say to her. He doubted that his thoughts on wave mechanics would be appropriate, though it was very interesting of course, and would be to anyone interested in the physical sciences. As Ann was. But perhaps not now. Now the sheer sensory array of water, wind, sky— it looked like it was enough for her. Perhaps silence was in order.