This painting was not in the show, but I saw it in London last year at the National Gallery. It is Turner's The Fighting Temeraire Tugged to Her Last Berth to be Broken Up, 1838. It shows one of the great naval ships of the Napoleonic Wars, ships that Turner loved since boyhood, being towed to drydock by a steamship to be scrapped. This painting includes one of the greatest sunsets in all of art. I've never in my life seen a sunset that looks like this (and at 50, I've seen a lot of them). It is Turner's great power as an artist that makes me believe in it even though I know better.
Hugh Honour, in his great book on Romantic art, includes these lines from PB Shelley's The Daemon of The World in his discussion of Turner:
If solitude hath ever led thy stepsTo the shore of the immeasurable sea,And thou hast lingered thereUntil the sun's broad orbSeemed resting on the fiery line of ocean,Thou must have marked the braided webs of goldThat without motion hangOver the sinking sphere:Thou must have marked the billowy mountain clouds,Edged with intolerable radiancy,Towering like rocks of jetAbove the burning deep:And yet there is a momentWhen the sun's highest pointPeers like a star o'er ocean's western edge,When those far clouds of feathery purple gleamLike faery lands girt by some heavenly sea:Then has thy rapt imagination soaredWhere in the midst of all exciting thingsThe temple of mightiest Daemon stands.