Not knowing about Meissonier in 1863 would have been like not knowing about Edouard Manet today. On the other hand, knowing about Manet in 1863 was like knowing about Meissonier now, which is to say, a sign of probable weirdness. All three of young Edouard's submissions had been rejected from that year's salon, among them a work called 'Le Bain', now known as 'Le Dejeuner sur l'herbe.' Two years later, another Manet, 'Olympia', was greeted by "epidemics of crazed laughter", with guards posted to prevent its attack. Yet, barely a century on, the historian TJ Clark dubbed 'Olympia' "the founding monument of modern art", even as a statue of Meissonier was being dragged from the Louvre on the orders of Andre Malraux.

So, what happened? One of the many engaging things about Ross King's book, The Judgement Of Paris, is that it doesn't really tell us. The easy answer would be to say that tastes in art shifted from Meissonier's perfect finish . . .

unmarked surfaces, Vermeer-like detail . . . to canvases on which paint had been laid quickly a la Manet; from archaic subjects to Baudelaire's depiction of modern life. Speed, the world viewed from a train, changed the way 19th-century Frenchmen saw. Manet celebrated this in 'Le Chemin de Fer', and swept the board. Meissonier had a railway built to watch horses gallop. He sank like a stone.

King is having none of this neatness, though. Just as Zola called the Paris Salon a ragout, so King's view of the history of art is stirred in with other histories: of horse racing, the Bonaparte clan, the Franco-Mexican War.

Even art history isn't as tidy as it looks. The antediluvian Meissonier's career began with a genuinely modern picture, 'A Remembrance of Civil War', 1848. His claim to have invented plein air painting may have been exaggerated, but he was working out-of-doors long before Manet was.

But the real fascination of this book is in King's linking of his subjects to events outside the art world. One reason for Meissonier's fall from grace was his identification with the Second Empire. 'Remembrance of Civil War' was seen as so seditious after Napoleon III's coup that the court fed Meissonier commissions to keep him from painting anything like it again. Thus the pierrots and ruddy drinkers. But it was also Napoleon who was behind the Salon des Refuses of 1863 where 'Le Bain' was first shown. Keen to distract public attention from reverses in his Mexican adventure, the Emperor insisted scandals like Manet's should be given a show of their own. "One of the first duties of a sovereign, " observed a shrewd Napoleon, "is to amuse his subjects." If less directly, Manet was as much the Emperor's man as Meissonier.

King's is a brilliant book, a micro-history that feels like a macro-history.

Apart from anything else, it is full of dinner-party titbits: Bonaparte falling off the Arcole Bridge; General Ducrot observing the surrounding Prussian army and sighing "We're in a chamberpot and about to be shat on." The Judgement Of Paris is a good read and good history; as unusual a pairing as its twin subjects.