AT THE press preview, San Francisco Mayor Gavin Newsom gave the best justification for the new show at the de Young museum, "The Birth of Impressionism: Masterpieces From the Musee d'Orsay": "It's better than storing them in a basement gathering dust." Good ol' Gavin.

This expensive ($21 advance ticket) show is the first of two helpings from the d'Orsay, which is temporarily closed for refurbishing for its 25th anniversary. The Parisian museum is known principally for its collection of Impressionist works, but those expecting sailboats and flowers will be in for a surprise. Like two cinematic blockbusters this year, Robin Hood and Alice in Wonderland, the advertised show turns out to be a prequel. It's a primer for how the revolution in painting (and seeing) took place.

I suppose the show argues that if there is such a thing as post-Impressionism, there should be such a thing as pre-Impressionism. But those looking for a clear narrative pathway to the Bridge at Giverny are sure to be confused. What became Impressionism was, first off, the work of Edouard Manet (represented here in 11 pieces), an internationally famous figure with a private income who didn't have to group with socially weaker artists to survive.

That independent streak was picked up by a group of outsider artists with distinctly non-salon proclivities. We see the roots of ashcan (in Falguiere's 1875 The Wrestlers) and social realism (Jules Breton's 1877 The Harvester, a colossal peasant brandishing a sheaf of wheat big enough to knock down a horse). It's a group of winding roads we have leading to the lonely, stony hills of Cezanne and the moody pastures of Pissarro. And what's Whistler's mother doing here? (Three people I met asked that question.)

Arrangement in Gray and Black, no. 1: Portrait of the Artist's Mother (1871) is misunderstood as a lampoon of the subject. Seen in flank view, she's a very old woman, the epitome of lace-capped homeliness. It's a much larger painting than you'd expect, and this size emphasizes the radical approach: the flatness assumed from Japanese art, the planes of color stark to the point of monochrome. It was a drastic, divisive painting, exposed to ridicule in its day. "Poor lady, posed like a sack of coal," mocked one cartoonist.

The Whistler painting is a breakthrough, an icon-blaster in a time favoring allegories and classical subjects. I also liked—maybe better than anything in the show—another non-Impressionist work, Gustave Moreau's 1865 rejoinder to standard classicism, Jason & Medee. It's a troubling painting of the pair entwined like Chagall lovers. The murderous wife Medea swoons at this teenage warrior, who is as golden as the fleece he stole.

There are compare-and-contrast pieces throughout: Courbet's 1873 The Trout shows the instant of a creature losing its life; the context of the Gulf disaster gives it all the more anguish. Everything but the fishy subject matter is different in Antoine Villon's 1870 Saltwater Fish, which exists only to show light reflecting on shiny, dark shapes. Bastien-Lepage's 1877 Haymaking, with the farmworker startled bolt upright after a nap in the field, shows a woman caught unawares, so hard-featured she looks like a troglodyte, wondering at the world to which she awakes. Smaller if equally fine is Tissot's highly sensual 1876 The Dreamer, depicting a lady of luxury stirring in her sleep.

The effect of railroad travel on art is a subtext of this show. Just as we started to get more abstract paintings of flat fields and geographical shapes after air travel became deregulated and cheap, the rise of rail in France prepared viewers for the shimmer of light: paintings as if seen through a window, traveling fast. Monet's 1877 picture here of the Gare Saint-Lazare crowned in steam suggests this love of rail. Vacationers now had cheap access to the cloudy French beaches to become bathers and of course, sailors, as we were to see in painting after painting.

The popularity of photography caused a rise in the informal image: Frederic Bazille's 1867 portrait of Renoir crouched with his heels on a chair; Degas' study of a lady getting a pedicure; Gustave Caillebotte's somber 1875 image of the hardest kind of work you can do indoors, of workers scraping a floor.

Impressionism exalted the informal, the earthy. Monet's delightful 1876 painting of a crowd of sophisticated-looking white turkeys, glowing like angels as they strut up a hill—the ridiculous fowl posed like birds of paradise—leaves us firmly in the hands of the movement to be and ready for September's follow-up.

THE BIRTH OF IMPRESSIONISM: MASTERPIECES FROM THE MUSEE D'ORSAY shows at the de Young Museum in Golden Gate Park, San Francisco, through Sept. 6. Tickets $21 adult, nonmember. 415.750.3600.

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