Guglielmo Giovanni Maria Marconi, 1st Marquis of Marconi FRSA (25 April 1874 – 20 July 1937) was an Italian inventor and electrical engineer, known for his pioneering work on long-distance radio transmission, development of Marconi's law, and a radio telegraph system, autographed letter on headed paper dated 19th January 1906 to Isental & Co, 85 Mortimer Street, "Dear Sirs, Confirming my conversation with you, I herewith send you formal order for one Mercury Jet Interrupter similar to the one you showed me, the said interrupter to be worked by means of a motor on a 16 to 24 volt circuit. I trust you will be able to deliver by next Monday as promised, Yours faithfully G. Marconi "

the letter is 25cm x 20cm, small tear to the central fold, with watermark for 'John Dickinson & Co, Superfine'

Note: This letter forms part of a collection recently discovered in the belongings of Adolf Isenthal. Letters from this collection have not been previously published.