A striking portrait by Joseph Wright of Derby (which hangs in Tate Britain) shows an elegantly dressed man reclining in a woodland glade, his right hand supporting his chin, his left resting on a book with a one-word title­ – Rousseau. The man is Sir Brooke Boothby, and he did more than anyone else to introduce Jean-Jacques Rousseau’s ideas to his fellow luminaries of the Midlands Enlightenment, in their strongholds of Lichfield, Ashbourne and Derby. Boothby brought Rousseau in person to Ashbourne in 1766 after his short stay in London with David Hume, and ten years later he visited him in Paris, where he was given the first part of Rousseau’s autobiography. This he published in Lichfield after the author’s death.

Lichfield’s two most eminent men were not impressed. Samuel Johnson declared roundly that ‘Rousseau, Sir, is a very bad man. I would sooner sign a sentence for his transportation, than that of any felon who has gone from the Old Bailey these many years.’ Erasmus Darwin, more measured, rejected Rousseau’s idea that social bonds constrain the natural man, placing him ‘in fetters’: rather, Darwin believed, such bonds are essential to the benign process of civilisation. Some, however, proved very receptive to Rousseau’s ideas – in particular his theories on education and the proper raising of children (as expounded in Émile). Overlooking the fact that Rousseau had abandoned all his own children, his disciples eagerly adopted his methods. Among these were the progressive educator, inventor and writer Richard Lovell Edgeworth (father of the novelist Maria) and his close friend, Thomas Day, a prominent figure in Lichfield’s intellectual scene, who collaborated in raising Edgeworth’s son Dick according to Rousseau’s methods.

Day’s devotion to the ideas of Rousseau was such that he once declared that, were all the world’s books to be destroyed, he would wish to save only the Bible and Émile. The educational experiment with Edgeworth’s son inspired him to try something more ambitious – to take a young girl and train her up to be a suitable wife for him. He had little luck in finding a wife ready-made – in large part, perhaps, because of his exorbitant requirements. As the poet Anna Seward, the ‘swan of Lichfield’ – who had herself turned him down – wrote: ‘He resolved… that his wife should have a taste for literature and science, for moral and patriotic philosophy. So might she be his companion in that retirement, to which he had destined himself; and assist him forming the minds of his children to stubborn virtue and high exertion. He resolved also, that she should be simple as a mountain girl, in her dress, her diet and her manners, fearless and intrepid as the Spartan wives and Roman heroines.’ No wonder there were no takers.

Day’s search for potential wife material took him to an orphanage in Shrewsbury, where he selected 11-year-old Ann Kingston, described by Seward as ‘a clear, auburn brunette, with dark eyes, glowing bloom and chestnut tresses’, and to the Foundling Hospital in London, where his choice fell on 12-year-old Dorcas Carr, ‘fair, with flaxen locks and light eyes’. The girls were handed over to Day on the understanding that they were to be servants in Edgeworth’s household, though no such arrangement had been made. He renamed Ann ‘Sabrina’ and Dorcas ‘Lucretia’ and took them both to Avignon, where he ensured their isolation by hiring only French-speaking staff and refusing to let them learn French.

To strengthen their constitutions, the girls were made to walk through torrential downpours and lie down in mud, and they were trained to obey him unquestioningly, trust him totally, and respect his wishes in all things. Among his educational methods, he would train them not to feel fear by shooting at their skirts with a gun that might or might not have been loaded (accounts differ), he dripped hot candle wax on them to inure them to pain, and, on one occasion, he taught them about the importance of oxygen by suffocating their pet chicken.

Fortunately, for Lucretia, Day concluded that she was ‘invincibly stupid’ and returned her to the millinery apprenticeship in London that had been her intended career. Day took Sabrina to live with him in Stowe House in Lichfield, where he continued her training. Before long, however, he decided that she was never going to make a suitable wife – her failure, of course, not his – and he lost interest. The unfortunate Sabrina had no idea that she was the subject of an experiment, and when Day’s friend John Bicknell, who had helped him select the girls, revealed the fact to her, she was horrified. Even so, she accepted Bicknell’s proposal of marriage, and went on to have two children with him.

It is hard to know what to make of Thomas Day’s experiment. Certainly, it would be viewed today as criminal child abuse, and his techniques – isolation, alienation, insistence on total subservience – are reminiscent of cult practice in modern times. But Day, like all ideologues, no doubt saw himself as acting from the highest motives and in pursuit of his (or rather Rousseau’s) firmly held beliefs. The idea of the individual as a tabula rasa – originated by John Locke and developed by Rousseau – led easily enough to the notion that a human subject could be moulded into any desired form, given the right conditioning and training. One could say that Day was a victim of ideology, of a Big Idea, one bigger than mere reality ­– but the true victims were those two girls, who were lucky to escape and make lives for themselves.

Happily, there was more to Thomas Day than his grisly experiment. He was a prominent abolitionist, and published a heartfelt poem, ‘The Dying Negro’ (co-written with his friend John Bicknell), that sold well and made a considerable impact. But his most lasting work was a highly moralistic children’s book, The History of Sandford and Merton, which sold in huge numbers for the best part of a century after its publication (in three parts) in the 1780s. In this long, discursive series of tales, Tommy Merton, the spoilt young son of a wealthy family, learns, under the influence of sturdy yeoman farmer’s son Harry Sandford, to despise the decadent trappings of wealth and high society, and embrace the simple life of honest virtue and hard work – all in keeping with Rousseauvian ideas.

Despite everything, Day did finally find a wife, one Esther Milnes, a Chesterfield heiress, who was obliged to live an ascetic life with him, giving up many social connections, luxuries and previous pastimes, including playing the harpsichord. They had no children, and, unusually for the time, Day allowed her to control her own finances, in case she should tire of this restricted life. It seems she never did. Thomas Day remained a victim of ideas to the end: one of his theories was that horses did not need breaking, but could be made amenable by kind treatment alone. An unbroken colt dramatically disproved his theory on a September day in 1789 by throwing him, with fatal results.