BOOK REVIEW : A Buoyant Portrait of the Enlightenment : A WOMAN, A MAN, AND TWO KINGDOMS; The Story of Madame d’Epinay and the Abbe Galiani, <i> by Francis Steegmuller</i> , Alfred A. Knopf, $23, 288 pages

From Paris, Mme. d’Epinay, fluent participant in that grand 18th-Century conversation known as the Enlightenment, wrote satirically about the monstrous hairstyles worn at the court of Louis XV: “On one lady’s head we see the reopening of the Parlement; on another, the Russian-Turkish peace treaty; on yet another, an English garden. . . .�

Her diligent correspondent, Abbe Galiani, brooding in rustication, replied with the hair news of the Naples court. The coiffures were 22 inches high and 15 inches wide, not including feathers, he reported. A woman’s face “in the midst of all that atmosphere , looks like a navel; a pretty navel chez vous , a hideous one chez nous .�

Mme. d’Epinay favored a simpler, more pastoral hairstyle. Her frivolity, like that of the Enlightenment, consisted in the display of witty common sense in a time of elaborate decadence. As for the Abbe, he had a tonsure; although in all other respects--knowing a lot about women’s navels, for instance--he showed few traditional clerical inhibitions.

Yet the play of intelligence pursued by Mme. d’Epinay and her circle, which included Diderot and Melchior Grimm as well as the Abbe, was also a hairdo. It was freer and infinitely more attractive, but in its own way it, too, was a stylization of the head that wore it.

It asserted an attitude: The pleasures of human possibility without the religious and feudal constraints. It was not, on the other hand, very good at pain; having neither the consolation of faith nor the other consolation, developed by the Romantics, of complaining.

In “A Woman, a Man, and Two Kingdoms,� Francis Steegmuller evokes the 18th-Century world of Mme. d’Epinay and Galiani. In his excerpts from their correspondence, we sense both the genius of their literary age and its limitations. The high notes come out with a fresh and intoxicating freedom; the bass is almost absent.

Yet Mme. d’Epinay had plenty of misery. Orphaned at 2, she married a romantic young cousin who promptly gave her the clap, flaunted his many affairs and ran through their money. She fought back, achieved some control of her finances and engaged in two successive long-term love affairs. The son from the first of these, in his turn, became her chief tormentor and sponge.

Galiani, a brilliant young man in Naples--he wrote treatises on money and on grain supply that were vastly admired--was sent as a diplomat to Paris. He stayed for 10 years, shone in the salons and made his enduring literary friendships. Then, for an indiscretion, he was recalled and spent the rest of his life in Naples feeling that he had been abducted by a comet and later returned to a stable. Only in his correspondence was he able to keep some of his old connections.

The burdens of these two lives, though Steegmuller lets us see them, are touched on lightly. Occasionally, there is a lamentation by Galiani; in his first few months in Paris, he hated the food, the climate and his own awkwardness.

From Mme. d’Epinay there are one or two somber notes as well. After two happy years in Geneva, in the company of Grimm, her lover and mentor, she was obliged to return to Paris and her tangled domestic affairs.

Grimm tried to cheer her up by telling her she was free to choose her life. She replied--and suddenly she is not the intellectual dazzler but any woman who has had to clean up men’s messes and put up with their rhetoric as well--�That is only the poetry of the situation.�

Mostly, the book portrays the buoyancy. Mme. d’Epinay comes through a little vaguely; we hear of the wit and the virtue but don’t quite see it.

Galiani, on the other hand, is a figure of immense color and light. Awkward, provincial and with only a middling diplomatic status, he won over Paris, and we can see why. His intelligence made him the cherished companion of Diderot, Grimm and others, but what truly captivated them was his spirit of enjoyment and comedy, often directed at himself.

Only 4 feet, 6 inches tall and ill-dressed, his first appearance at Versailles to present his credentials as secretary of the Naples Embassy provoked titters. But in France, a phrase will conquer a king. “What you see is but a sample of the secretary; the complete secretary will come later,� he announced. The court melted. It was true, furthermore. He gained envied access to Choiseul, the arrogant foreign minister. The latter used him, of course, and ultimately betrayed him.

He enchanted Diderot, the Enlightenment’s true saint and prophet. Diderot recalled how everyone would brighten up when Galiani arrived at one of Mme. d’Epinay’s gatherings. “A treasure on a rainy day,� he called him. “If one of the people who carve chessmen were to make some pieces in his image, everybody would buy one to take home.�

We get a picture of the diminutive Abbe, sitting cross-legged in an armchair by the hearth, flushed with the heat and his own sallies, holding his wig in one hand and gesticulating with the other.

Steegmuller’s portrait has gaps in it; evidently the material is spotty. There is some padding, though much of it is entertaining and useful, in the form of snapshots of the time taken from the European newsletter edited by Grimm.

But if the book sometimes seems impressionistic, its success lies in the fact that we would like to know much more about its Abbe; we want a biography.

Next: Christopher Goodrich reviews “Goodness� by Tim Parks (Grove Weidenfeld).