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Graham Farmelo (Books, THES , January 17) repeats the assertion that "Margaret Thatcher deserves credit for the role she surely played in securing Faraday's place on the English ?20 note". It is not at all clear what influence, if any, she exerted in this decision.

As director of the Royal Institution in the late 1980s, I set about convincing the Post Office and the Bank of England that Michael Faraday's image should be publicised to mark the bicentenary of his birth in 1791. In spring 1991, the Post Office issued a first-day cover and a 22p first-class stamp carrying Faraday's image.

Shortly thereafter, Irena McCabe, the institution's archivist, and I were invited to the Bank of England printing works for a private viewing of the Faraday ?20 note.

In assessing the worthiness of Faraday: That Life , it is not necessary to consider whether or not an ex-prime minister would love it.

John Meurig Thomas
University of Cambridge