A portrait of Thomas Day in later life shows a fat, plain fellow swathed in pink satin with the constipated gaze of a man who is either very clever, or very up himself, or both. He was born rich and inherited more, was brutalised in the accepted English manner at Charterhouse and found himself among allies at Oxford. He formed his opinions early and strong, and held to them for the rest of his life. Despite being considered dull, he did make lasting friendships, particularly with Richard Lovell Edgeworth, later the father of the novelist Maria Edgeworth.

But while Edgeworth was charming, good-natured and successful with women, Day was not. His status ensured him access to the best and brightest women in Georgian society, but most found his manner unpleasant and his opinions gauche. Far from being discouraged by his lack of success, Day took it as proof of women's feeble breeding. "Love, I am firmly convinc'd, is the Effect of Prejudice & Imagination; a rational Mind is incapable of it." Thus defended, he set out on his first and greatest project: to create for himself the ideal wife.

Inspired by the writings of Jean-Jacques Rousseau, Day "resolved to breed up two girls, as equally as possible, under his own eye; hoping that before they grew up to be women, he might be able to decide which of them might be most agreeable to himself". Aged 22, Day bought two 12-year-old girls from an orphanage, renamed them Lucretia and Sabrina, and began re-educating them. His ideal woman should, "have a taste for literature and science, for moral and patriotic philosophy simple as a mountain girl in her dress, her diet and her manners, fearless and intrepid as the Spartan wives and Roman heroines". Lucretia proved intransigent so was dropped early on, but Sabrina was charming, pretty and tractable.

At the same time as Day was training up Sabrina, he was also looking elsewhere. Having decided that Honora Sneyd  intelligent and independent  met his criteria, Day sent her a parcel containing his proposal of marriage, his expectations of what rights and benefits that marriage would confer and his intention that from now on she she should see almost no one but him. Honora rejected him. He tried her sister Elizabeth. She rejected him too. Another Elizabeth was discarded because she wore diamonds to one of their meetings, and, "no wife must ever have earrings in their possession". Finally, Day met Esther Milnes, who despite being subjected to several months of rigorous wife-training, remained steadfast. They married in 1778 when he was 30 and she 25.

Sabrina, meanwhile, had become something of an embarrassment. Initially Day sent her out to various friends and employers, though word of his strange project had already begun to spread. Just as Sabrina found a settled position as a school housekeeper, the first of many versions of her tale was published. Despite this, Sabrina eventually married another friend of Day's and had two sons, one of whom was ashamed to discover her foundling origins when they were exposed again in print.

Over the years, everyone who either knew them or knew of them, including Maria Edgeworth, Fanny Burney, Anthony Trollope, and  later  Henry James and George Bernard Shaw took the idea of Day's real-life Pygmalion and made literary myth of it.

Wendy Moore's version is as heavily editorialised as many of the fictional equivalents. She has done an exceptional job of tracking Sabrina through the records and produced a cheerful, lively version of her tale. But because the material available doesn't really stretch to full book length, Moore plugs the gaps with occasionally heavy-handed guidance of her own. In the end, the story falls on its own reality  Day is too unsympathetic a Higgins and Sabrina too quiet for a true and cautionary Doolittle.

In June 1769, 21-year-old Thomas Day and his friend John Bicknell went to the Orphan Hospital in Shrewsbury to select a prepubescent girl for Day. This was not a gesture of charity to remove the girl from her destitute situation but an experiment in which Day was trying to create his "perfect wife".

Born in 1748, Day had inherited a fortune from his father, a prosperous government official. He went to boarding school, where he thrived in the harsh regime of cold baths and punishments. He was clever and excelled in school and later at university. Dressed shoddily and with unkempt hair, Day eschewed the conventions of fashion, etiquette and status, preferring to wash himself in streams and live a simple life, withdrawn from temptations and comforts. And he needed a wife to join him.

After several unsuccessful attempts to find one, Day decided to mould one himself, in the manner of Pygmalion. He wanted a wife who was clever enough to discuss philosophy, astronomy and literature, while at the same time being entirely devoted to him and compliant to his wishes. She would need to be physically resilient to withstand the austere life that he envisaged, but at the same time gentle and caring. She should be young and beautiful like a goddess and "virginal like a country maiden".

Day, like many of his friends, was inspired by JeanJacques Rousseau's ideas of returning to nature, and in particular by his novel Émile, or on Education. Rousseau's thesis was that children were essentially good, but became corrupted by society and the influence of civilisation. In Émile he argued that education should protect children from this disturbing influence: the boy Émile is breastfed by his mother, allowed to roam freely through nature and is never scolded, while at the same time being shaped into a strong man by enduring the hardships of cold, hunger and pain. Day decided to use the same system to create a wife for himself.

At the Shrewsbury orphanage he chose a 12year old with auburn ringlets, but within a few weeks he was at the Holborn branch of the Foundling Hospital in London, picking a second girl  this one with "flaxen locks". He would educate them both, and whoever turned out better would become his wife  a promise he sealed with a contract. Protected by his wealth and rank, Day had purchased these girls, Wendy Moore writes, as easily "as he might buy two shoe buckles".

Over the next year Sabrina and Lucretia were required to carry out household chores while learning about physics, geography and astronomy, and they were kept entirely ignorant as to Day's real intentions. According to one of Day's friends, Lucretia turned out to be "invincibly stupid", and so he decided to concentrate on Sabrina. While Lucretia was placed as an apprentice in a milliner's shop, Sabrina's ordeal was only just beginning.

As Day was planning a life of austerity, the girl had to be "educated" to withstand all kinds of physical hardships  cold, pain and terror, all in accordance with Rousseau's scheme in Emile. Day's extraordinary methods included dripping hot wax on to Sabrina's naked arms and shoulders (ordering her not to cry or move) and shooting guns at her skirts or close to her ears without warning (again, she was told to remain still). Maybe most astonishing of all was that Day lived openly with Sabrina in Litchfield among his friends of the Lunar Society, a circle of scientists, thinkers and industrialists in the Midlands which included Erasmus Darwin, the inventor Richard Lovell Edgeworth and the chemist James Keir.

Day's experiment didn't work out. Sabrina, he told his friends, "failed to meet his expectations". After two years, she was dispatched to a boarding school and Day resumed the search for a perfect wife among his peers. Over the next years he went through a staggering number of engagements and declarations of love  but each time something went wrong. One woman refused to marry him after he presented her with a list of expectations and a "proposed mode of living" that included complete seclusion from society, while another was discarded because she wanted to keep her diamond earrings.

Day was a paradoxical character: he became known for his charitable work, giving away much of his fortune to the poor though never giving much thought about Sabrina and her wellbeing after he abandoned her. He was an adamant abolitionist while at the same time making Sabrina practically his slave.

In the end, Day married Esther Milnes, an accomplished heiress and poet who became completely submissive to his will. Sabrina, meanwhile, spent several years at boarding school, was apprenticed to a dressmaker and then married Day's old friend, John Bicknell. It was only then that she learned the full extent of the experiment, but when she demanded some explanation from Day, he replied: " whether those intentions were wild, chimerical, & extravagant  that object relates to myself alone & you are the last person in the world to whom I owe any apologies".

Within three years she was a widow, left with two young sons and no money because Bicknell had gambled everything away. She became a housekeeper at a boarding school in London and died aged 86, but not before she had suffered the humiliation of her story becoming public in a series of biographies.

As in her previous book, Wedlock, which portrayed Mary Eleanor Bowes and her disastrous and cruel marriage, Moore has again found an excruciatingly gruesome and fascinating story. But instead of turning these portraits into misery biographies, she weaves them into the broader context of the time. In Wedlock, she told a tale of evil and dependency, folded into the ideas of marriage and divorce in the late 18th century  and in How to Create the Perfect Wife, she investigates education, liberty and the role of women. It is pleasing to see a writer bringing together painstaking research with gripping storytelling. I can't wait for her next book.

 Andrea Wulf's Chasing Venus is published by Heinemann