The dealers had bought the items in good faith but were later contacted by police in the US following an investigation of an alleged theft from the Carnegie Library of Pittsburgh in Pennsylvania.
It emerged that a US dealer and a librarian had been charged with, among other offences, theft, receiving stolen property and forgery.
John Schulman, 54, co-founder of Caliban Book Shop and Greg Priore, 61, of Oakland, who worked as the archivist and manager of Carnegie Library’s rare book room since 1992, were charged earlier this month.
It is alleged that Priore took books and pages from the library and sold them to Schulman, who then sold them on through auctions and the trade.
There was an audit of the library last year and an investigation was launched. Police from the US interviewed London dealers earlier this year and were able to track down some of the missing books.
Harrington had bought Isaac Newton’s Philosophiae Naturalis Principia Mathematica for £72,500 and sold it to a private collector for £145,000 five years ago. Another library book was sold through Maggs.
Both dealers said they had no reason to question the books’ provenance as libraries often sell works to raise money and these books came with what looked like official deaccessioning stamps.
Pom Harrington of Peter Harrington told ATG: “We had sold the book to a collector in London and had to give the money back. We restituted the book to the authorities at our expense.”
In his view he said the “library should have audited more frequently – not once in 26 years”.
Speaking to ATG, Ed Maggs commented: “This has been a very disappointing and disruptive episode, but we’re glad to have been able to return the two books that unwittingly went through our hands, and we mourn the damage done to other books from this library which had plates removed.”