NIGHTS AT THE CIRCUS : <i> by Angela Carter (Viking: $15.95; 295 pp.) </i>

The thesis novel; what a heart-sinking notion. It suggests the same relation to literary beguilement that the metronome has to music.

Angela Carter’s novel quivers with ideas about many things, including feminism. It hums and buzzes and stamps its feet even at the rare moments when it is standing still. Yet, its ideas are not theses but hypotheses. “Nights at the Circus” is not about how men and women ought to be, but how they just conceivably might be. Instead of defining and fixing its characters, this shaggy and ebullient tall tale grows them out of a generous compost of contradictions.

It is a blather book, bursting with talk. Its heroine, Fevvers--I keep thinking of her as Angela--is a kind of female Gargantua; yet the book’s giantism is wonderfully misleading, being, in fact, essentially fragile and human-sized.

“Nights” is set in the last days of 1899, dawn of a Century of Progress and the New Woman, as one of the characters pronounces. Grandiloquence and irony are paired from the very start. This is how life is, they affirm: a wispy tendril cracking the wispiness that masquerades as concrete.

The New Woman is Fevvers, gorgeous and outsized toast of Europe, a Cockney circus artist painted and loved by Toulouse-Lautrec, and wooed but not won by England’s corpulent crown prince. Fevvers is the world’s greatest trapeze flier, owing to the fact that she has wings. Six feet long and dyed purple from their original pale blond, she confides. (Their original color, in fact, like that of her blond hair, is sparrow brown. For every bedrock truth there is a moldier truth scrunched underneath the bed.)

In the book’s first part, Fevvers is being interviewed in her dressing room--a swamp of soiled underwear, pots of makeup, billets-doux and spilled champagne--by Jack Walser, a gung-ho American journalist who has covered wars, insurrections and disasters around the world. It is a duel--or so it seems for a while--between Legendary Woman and Legendary Man.

Jack is “a kaleidoscope equipped with consciousness.” In his adventures, “his inwardness was left untouched,” and he retained “the privileged irresponsibility of the journalist, the professional necessity to see all and believe nothing.” He proposes to use Fevvers as part of a series about the great humbugs of the world.

Yet, from the start, he is overwhelmed. Her 30-foot leaps could be done by wires, but only real wings could account for her ability to do triple somersaults slowly. “A projectile cannot mooch along its trajectory,” he reflects. And then comes a deeper realization. Fevvers’ success depends on the public’s suspicion that she is a fake. If her wings are real, then she is no illusionary marvel, but simply a freak. “In a secular society, an authentic miracle must purport to be a hoax in order to gain credit in the world.”

It is not wings and flight alone that mesmerize Jack, but Fevvers’ beautiful excess. There is her size, her looks--as coarse, stunning and limpid as a country girl’s--and the tale of her life from the time she was found as an infant lying among broken eggshells on the steps of a brothel, to her present international celebrity.

The tale, told in spellbinding detail, is oddly prolonged. Lizzie, Fevvers’ wet nurse and now her dresser and strategist (it was Lizzie who prepared graphs of weight and wing span to teach Fevvers to fly), has her own witchery. She can make time stand still, thanks to a clock she carries in her huge purse. She also carries other bits of limited magic, among them devices that allow her to inflict athlete’s foot, piles and depression upon Fevvers’ enemies. The purse, that mysterious jumble of feminine disorder, is made, quite wonderfully, into a domestic conjuring device.

By the end of the night, as prolonged by Lizzie’s purse, Jack is hopelessly in love. He joins the circus that is about to take Fevvers on a grand tour of Russia. He relinquishes his journalistic status and detachment for the grueling work and the humiliation of an apprentice clown. It is the first stage of his transformation.

The circus portion of “Nights” is entrancing. There is a splendid portrait and meditation upon clowns, an account of a troupe of apes who oust their human master, the love of a woman tiger tamer and a girl who joins the circus as a waif and becomes a singer, and the expansive scalawaggery of Col. Yeager, the proprietor, whose principal adviser is his pet pig. Carter’s characters are magical and believable at the same time; and along with the gaudiness of the circus’ adventures, a purpose is being advanced. Jack, as stumbling clown, has begun to undermine the Man-Woman duel and penetrate Fevvers’ defenses. In the book’s last section, she too will change.

The train is dynamited halfway across Siberia by bandits intent on getting a message to Queen Victoria--they assume Fevvers is on intimate terms with her--about the oppressive conditions that turned them into outlaws. The explosion fragments the narrative. A band of escaped female convicts wanders by on its way to set up a women’s republic--rather distractingly, in view of the accumulation of incident at this point. Fevvers, Lizzie and other members of the circus take refuge in a ramshackle hut housing the Transbaikal Conservatory of Music and its hermit director.

Jack, knocked out by the explosion, comes to in a state of amnesia, and is taken in by a tribe of woodsmen led by a shaman. Carter’s irony perpetrates a splendid reversal. The shaman is entranced by Jack’s hazy recollections of his purposeful late-Victorian life. He finds in them the equivalent of his own dream-states, and he grooms Jack to be his successor.

Before this can happen, Jack recovers and is reunited with Fevvers. She has changed, too. Without her circus, her public, her lovers, Fevvers’ magnificent autonomy wilts. Her wings molt; her feathers and hair turn mousy. She revives only when she finds a wood-man audience and Jack. As she approached him, “already she felt more blond.”

Carter allows for many ways of being a woman and a man. She writes touchingly about the lesbian union of tiger-tamer and singer; and about the wanderers in the all-woman republic. Her achievement with Fevvers and Jack is to mingle glories and contradictions. Fevvers’ magnificence is vulnerable. As for Jack, he has gone from male manipulator to clown to profit; yet, at the end of the book, he is preparing to write his long-postponed articles. He is also making love with Fevvers and taking the underneath position because of her wings. Men are men and women are women, we understand at the end of this abundant and invigorating book, and their capacity for transformation is a perpetual wonder.