He demonstrated their existence in his lectures to the Royal Institution by coating sheets of paper with a thin layer of melted wax, pouring on iron filings and then moving them with bar magnets beneath. As the wax hardened the circular patterns created were fixed in place.
Faraday gave these iron filing diagrams to friends and colleagues and there are many examples in the Royal Institution archives and others elsewhere. However, it is rare to see one for sale.
This example fixed on waxed blue paper, 4 x 5½in (9.5 x 14cm), was offered for sale at Dominic Winter in South Cerney on December 11. It came in for sale from a member of the trade with what proved an appealing estimate of £500-800.
Tipped onto a contemporary album leaf it was neatly inscribed in ink beneath Lines of magnetic [force] by Faraday given me by Mr Sydney on my visit to him on June 21st 1872.
‘Mr Sydney’ was the Rev Edwin Sidney (c.1798-1872), rector of Little Cornard, Suffolk, from 1847-72. A sometime lecturer at the Royal Institution, he occasionally corresponded with Faraday, his letters forming a small part of the six-volume Michael Faraday Correspondence.
Dominic Winter specialist Chris Albury described it as “both artwork and science item in one” and was deluged in interest from dealers and collectors from both sides of the Atlantic. A UK collector in the room who opened the bidding stuck with the competition, ultimately winning it at £10,000 (plus 20% buyer’s premium).