The risqué secret behind an 18th-century bestseller

Had he been alive, the Earl of Rochester would probably have let slip a lascivious chuckle. The austere Earl of Roscommon? Aghast, most likely.

An Oxford University academic has discovered that the phenomenal success of a collection of poems by the two peers was fuelled by an assortment of lurid pornographic rhymes, hidden at the back of the book.

The Works of the Earls of Rochester and Roscommon was one of the 18th century's bestselling poetry miscellanies, reprinted at least 20 times. Previously its popularity had been put down to Rochester's reputation for bawdy and the sensational, or for Roscommon's high-minded musings.

That was until Dr Claudine van Hensbergen found an array of poems located at the back of the book, with separate page numbers. Named "The Cabinet of Love", there was little indication as to what kind of work it included. "To my surprise, 'The Cabinet' turned out to be a collection of pornographic verses about dildos," said Dr van Hensbergen. "The poems include 'Dildoides', a poem attributed to Samuel Butler about the public burning of French-imported dildos, 'The Delights of Venus', a poem in which a married woman gives her younger friend an explicit account of the joys of sex, and 'The Discovery', a poem about a man hiding in a woman's room to watch her masturbate in bed."

One verse of "The Discovery" reads: "Then from the Table she her Garment took/Where, in her Pocket, was a bawdy Book/Which she remov'd, and thence drew out a Tool/Much like to that with which Men Women rule/She it apply'd where I'm asham'd to tell/And acted what I could have done as well/Soon from her Womb a slimy Matter sprung."

"In later years, a celebratory poem about condoms was added, as well as several obscene botanically themed verses attributed to 'a Member of a Society of Gardeners' in which male genitalia is described as the 'tree of life'," said Dr van Hensbergen.

She said the verses made her laugh, rather than blush: "The minute I started entering the poems, I realised what it was. It wasn't shocking to me, but it made me think about the obsession with curiosity in the 18th century in a slightly different way. I emailed the digital miscellanies team and said 'we've found another interesting thing'."

"The Cabinet" first appeared in the miscellany's second edition, published in 1714. The book's high sales were driven by word of mouth and in subsequent reprintings the salacious insert was moved to the front of the book.

It was printed by Edmund Curll, a publisher with an infamous lack of scruples. He was later imprisoned for printing obscene works, and tried in the House of Lords for publishing unflattering words about peers. His name was adopted in the coining of the term "Curlicism" for literary indecency.

It is believed that the inclusion of "The Cabinet" alongside work by Rochester, whose given name was John Wilmot, helped cement his reputation as the original English libertine. The Earl's satirical and often sensational poetry frequently included obscene language and imagery, though most often his intention was to represent the dark side of society's underbelly rather than merely to titillate.

Dr van Hensbergen's research also reveals the diverse reading tastes of the 18th century. "'The Cabinet' is unusual because it shows us that people read pornographic writing directly alongside the verse of major poets. This raises interesting questions about what counts as literature and where the boundaries between high and low culture lie. These ideas were much more fluid in the 18th century than they are today."