JEANNINE ALTON says you cannot fail to be lured by the Triumph of Eros exhibition on loan from St Petersburg

The Triumph of Eros: Art and Seduction in 18th Century France. That's the lip-smacking title of the latest collaborative exhibition at Somerset House, fruit of the 2003 alliance of the Courtauld Institute and the Hermitage Museum at St Petersburg.

Further temptation comes from the news that it includes a recently discovered collection of erotic engravings assembled "probably in secret" (it says here) by Tsar Nicholas I. Actually, I doubt very much that the imperial Tsars needed to keep their collections secret. Much more important for us today is that the engravings were kept away from light and are in pristine condition.

The exhibition focuses on the Regency and the reign of Louis XV, the Rococo period in fact, and all that implies by way of luxurious materials, high-grade craftsmanship and decoration verging on but never quite tumbling into the overblown and extravagant. It's also essentially catering for an elite of connoisseurs and courtiers. The social satire of English art at the time has no place here.

Like all major exhibitions, this one has a Theme, in this case the god of love, Eros or Cupid, envisaged as a reaction to a preceding age of rationalism. This won't really do. Many of those paintings, engravings, and the illustrated books, draw on the Contes of that quirky 17th-century figure La Fontaine, who didn't spend all his time writing fables about the animal kingdom.

The central figure of the show, seen for the first time in London, the large (life-size, presumably) marble Menacing Cupid by Falconet, was commissioned by Madame de Pompadour in 1757, the year after Voltaire's Candide took its first dry look at the world.

Anyway, Cupid presides over the suite of rooms, each assigned a mini-theme which disperses the paintings by, for example, Boucher which one would quite like to see together. And he's abundantly present, chubby, a bit pouty, sitting, flying, delivering letters, watching and pointing. His usual victim is a young girl, thus ensuring a plentiful display of bosoms and unreliable drapery.

His mother, Venus, is there too, in a series of engravings of works by Bouilliard, The Education of Cupid, (1783) definitely once owned by the Tsar, and in the huge Guérin oil, Venus and Nymphs.

Making excellent use of a narrow corridor, the Tsar's newly-found engravings occupy the theme of Love letters', again primarily showing young women en deshabiile or in bed, quivering with emotion as they receive or answer a billet-doux, that essential go-between. Cupid himself proffers his arrow as a pen for such a task.

The influence of the English epistolary novel can be seen in an illustration to Richardson's Pamela and one from the greatest example of them all, Les Liaisons Dangereuses.

By far the most erotic work appears under Encounters and Transgressions. Here are two tiny oils by Subleyras (based on La Fontaine. of course), commissioned in 1732, never seen in London and probably little elsewhere in view of their subject-matter.

Here is also a large oil by Nattier (1711) of Potiphar's Wife. Watteau's La Boudeuse is fascinating; a young girl, black-clad and rigidly upright, sits next to a lounging man in feathers and velvet. He fumbles in his doublet. Is he a letter-bearer? She averts her gaze - or does she? Strangely, there's only one kiss in the show - Fragonard's Serment d'Amour with attendant Cupids.

So far, I've only mentioned paintings. The exhibition has much more - books, for instance, though these are a little disappointing - illustrated copies of La Fontaine, and, oddly, the plays of Corneille. I think it's there to show the small format of these forbidden' books, but if there's erotic content in that pillar of rectitude I've wasted my life.

But the jewels, snuff-boxes, clocks and watches, and glittering Sèvres porcelain are masterpieces beyond price - fun too, like the gilt and painted stand with Cupid drumming on the inkwells.

The exhibition is on till April 8, just the thing for pre-spring flatness. For more information visit the website of Somerset House on the Strand: www.somerset-house.org.uk