That Hamilton Woman : THE VOLCANO LOVER: A Romance, <i> By Susan Sontag (Farrar Straus Giroux: $22; 440 pp.)</i>

Susan Sontag at play. That is not remarkable in itself. Double-domes make their stabs at levity: George Will writing about baseball; Chief Justice William Rehnquist capering solemnly--I saw him--in an amateur production of “Patience”; John Kenneth Galbraith trying his hand at an academic novel.

What sets “The Volcano Lover” apart from such heavy-footed exercises is not just that it is light-footed but also that, as play, it is both great fun and serious fun. Writing what I suppose could be called a historical novel about the celebrated and sloppy triangle of Admiral Horatio Nelson, Lady Emma Hamilton and her celery-stalk husband, Sir William Hamilton, Sontag condescends not at all.

The cross-country impetus of her thinking is as nervy as ever. But it is transmogrified. It is ideas as a game--real ideas and real game--as sentient and agile as a choreography of Michael Jordan’s sneakers.

Sontag tells a story and tells it extremely well, with speculative digressions and comment that serve, as in “Tristram Shandy,” to open the picaresque mental landscape through which the narrative marches. When the digressions are a trifle long-winded, it almost seems like human respect; a witty person may be long-winded but this can be an amiable trait, like corpulence; you don’t just shut it off.

She also respects her story. It is a vehicle to say things about women and their mismanaged fires--the volcano of the title, which nicely arranges to be Mt. Vesuvius as well. It speaks about men and their vulnerable outrages, about the English character, about the frailty of revolutions and the deadly power of counterrevolutions, about the inhuman aspects of art and power, and the richly decomposing stew of history that is Naples, where the book is set.

But it is an invigorating story in its own right. Sir William Hamilton, distantly connected to the king, finds himself Minister to the Court of Naples at the time of the French Revolution. (He had hoped for Madrid, but his connection was too puny.) He is a chilly egotist whose ruling passion is collecting art, antiquities and scientific specimens; notably, fresh lava scooped up at personal risk from the perpetually rumbling Vesuvius.

A depth in Sir William responds to the volcano’s own churning depths, but his ingrained response to being moved is to collect. Thus, when his seemingly complaisant wife dies, and his nephew sends over a discarded mistress to get her out of the way, Sir William is smitten to the point of making a scandalously unsuitable marriage.

Emma is a former artist’s model who worked--just how, is left to the imagination--for a doctor specializing in the cure of impotence. She is vulgar, ravishing and a vital force; she ravishes Sir William. Imprisoned in his overbred nature, he can only treat her as an objet d’art.

Among Sontag’s many bravura interjections is the argument that collecting is essentially a masculine activity. It stems from a man’s innate and oddly isolating assurance that he has a place in the world and, conversely, that the world belongs to him. Women, paradoxically, are too close to the world and too responsive to it to command such gassy assurance. Similarly--the connection is arcane but inveigling--it is only men who can tell a joke properly.

Emma the volcano can be collected no more than Vesuvius can. When young Nelson sails in, to protect Naples from Napoleon and to prop up the dissolute Bourbon king and his ferocious Hapsburg wife, the grand passion ignites. It sustains itself through Nelson’s triumphant comings and goings, and through a brief menage a trois residence in England. (Having lost ownership of his prize collectible, Sir William stays on as a kind of curator; there is a splendid image of him and Nelson fussing together over the household accounts.) After the husband’s death and Nelson’s own death at Trafalgar, Emma perishes in destitution despite the hero’s dying plea to his countrymen--grateful, but only just--to look after her and their child.

Nelson is an imp of fame; willful, avid, innocent and cruel. He is not quite real. Reality is a burden that rather hampers history’s great achievers, and Sontag’s Nelson is all the more effective in his will- o’-the-wisp character of a sanguinary Peter Pan. I sense a wry suggestion in Sontag’s sunny feminism, which manages to be both stirring and mocking, that male reality can also be a burden to the passions of a Real Woman.

Certainly Emma is a Real Woman. A ravishing milkmaid beauty when she comes out from England, she stops Neapolitan passers-by in their tracks. She brings her cheerfully Hogarthian mother with her, and the latter’s dryly disenchanted account in one of the book’s several epilogues is shrewd and terribly moving.

Emma’s vitality is unquenchable, and so is her redoubtable determination to fly upward like the sparks. Her vulgarity is one of her most appealing qualities, the polar opposite of camp. She is a great success at the Neapolitan court, where spontaneity seems exotic. Her looks soon go, and she grows fat, but she never doubts her right to a grand passion. Fortunately, neither does Nelson. He finds her magnificent, and that may be his most endearing quality.

It is Hamilton, though, who is the most remarkably rendered of the characters. Never has a frozen sensibility been so suggestive. Before he meets Emma, he acquires a pet monkey. The monkey loves him but Sir William wants a jester, not a child, Sontag writes. He spurns the monkey’s snuggle and teaches it tricks instead. Obediently, it performs. The Englishman has turned a loving thing into a collected thing. With Emma, of course, he fails. She never does manage more than affection with him; at the end, it is he who is collected.

The portrait is devastating, yet lightened with humor and understanding. There is a wonderful confrontation between Sir William and Goethe, who admires the Minister’s collection as a means to understand the principles of nature. For his pragmatic host, it exists for its own sake. In a shrewd evocation of her very male and very English protagonist, so lordly and so impotent, Sontag writes:

“His is the hyperactivity of the heroic depressive. He ferried himself past one vortex of melancholy after another by means of an astonishing spread of enthusiasms.”

There are other suggestive figures, among them Hamilton’s first wife, whom we come to recognize as a dormant version of Emma’s spurting volcano. There is the decadent greed of Naples’ Bourbon king, who eats and fornicates prodigiously, kills great quantities of game, butchers it himself, and sells the meat to his soldiers.

There is a fascinating portrayal of the short-lived Vesuvian Republic, set up by intellectuals and aristocratic idealists after the example of the French Revolution, and with Napoleon’s fickle protection. Its repression is brutally managed by the king and queen from their refuge in Sicily, implacably enforced by Nelson in England’s interest, and haplessly abetted by the Hamiltons. It is a wonderful reflection on the relative strengths of idealism, bloody reaction and a Great Power’s chilly reasons of state. With one of the executed revolutionaries, the poet Eleonora de Fonseca, Sontag makes a brief proxy appearance, much as Hitchcock used to do but with more charm.

We require stories. We can do without them for a while. We can read stories about the impossibility of telling stories, or stories that caution us against imagining that there is anything to them but our own arbitrary readings. But eventually, we require them.

It is a problem for a contemporary writer who wants to do more than retail personal sensibility, regional color or besieged childhoods. Stories imply a pattern to life; perhaps our lives have none.

History, on the other hand, indubitably does have a pattern, even if it is imposed contemporaneously and handed down. A number of writers have tried to use historical pattern to provide a story upon which to explore their insights and sensibilities. Sontag satirizes the process at the start of the book. She writes of a figure--we recognize her in her jeans and white silk blouse--meandering through a flea market and picking something out almost at random.

The story she has picked out she writes with entire fidelity and with all of a novelist’s art. Her contemporary interjections--digressions, questions, exclamations--in no way dilute or deflect the narrative. They do not weaken its three dimensions; they add a fourth which, without removing it from its time, brings it into ours.