An extensive Joseph Conrad collection, which includes Sylvia Plath's annotated copy of Lord Jim, is to grace the auction block at Sotheby's London on July 10-11.

Sylvia Plath pictured in 1957

Conrad, a Polish-born writer who is best known for his literary novels, such as Heart of Darkness (1899), The Lagoon (1896) and The Secret Agent (1907), is regarded as one of the finest English language writers of the late nineteenth and early twentieth centuries.

Wealthy, American-born collector Stanley J Seeger compiled the phenomenal collection over several decades. It includes letters, manuscripts, first editions and annotated proofs by Conrad, as well as Sylvia Plath's copy of Lord Jim, which is inscribed by her husband Ted Hughes: "I read the novel, this copy, aloud to Sylvia, in the evening, while she was making her rag rug - 1962."

Plath, who probably annotated the work in the spring of 1952, while studying twentieth century literature at Smith College Cambridge, committed suicide in February 1963.

Eminent novelist Joseph Conrad pictured in 1904

Plath's extensive annotations and underlining, some in green felt tip, reveal her wry sense of humour. In the author's note Plath has underlined Conrad's comment regarding "Thinking it over for something like 16 years", adding, "Never commit yourself hastily, I always say!"

Interest in items relating to the American-born confessional poet has increased dramatically of late. Plath's working papers for her poem Sheep in Fog sold at Bonhams on May 8 for £37,250 ($58,015). The sale represents the first time a manuscript by Plath has appeared at auction, and therefore the price achieved is a new auction record for any work the writer.

Sotheby's Peter Selley, an expert in books and manuscripts, told the Guardian newspaper: "This is the greatest single author collection pertaining to a modern writer to come to auction in living memory."

Before gaining employment with Sotheby's, Selley helped Seeger to assembler the collection.

Selley comments: "He was an intensely private man…we would never speak to him or see him. We would get a fax saying Mr Seeger would like to go ahead with the order.

"Book collecting is an intimate, solitary activity," Selley told the Guardian, "And he clearly had this strong affinity and deep passion for Conrad which is reflected in the collection."

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