I would like to thank the staff at the British Library of Political and Economic Science for allowing me access to their main collection and for the many occasions when they have helped me to find what I was looking for. The same thanks are due to the staff at the Science, Technology and Patents Branch of the British Library at Southampton Buildings, the Science Museum Library at South Kensington, and the Public Record Offices at Chancery Lane and at Kew.
Some points that puzzled me were cleared up by visits to the Greater London Record Office, in Northampton Road, and the Essex Record Office at Chelmsford. In both places the staff were most helpful. Correspondence with the National Museum of Labour History, in Manchester, and with the Library of the Royal Aeronautical Society, produced prompt answers to my queries for which I am most grateful.
The extracts from patent specifications, which have been used as illustrations in this book, have been reproduced by permission of Her Majesty's Stationery Office, Publication Division (Copyright), at Norwich. Where Crown Copyright is still in force the illustration is marked accordingly. Permission to publish the text of Marconi's letter to the War Office was kindly given by GEC- Marconi Ltd., who own the copyright. The original letter itself is the property of Her Majesty's Government and is in the custody of the Public Record Office at Kew. The full PRO reference is given in Chapter 5.
Professor David Vaver, Professor of Law at Osgoode Hall Law School, York University, Ontario, and Editor in Chief of the Intellectual Property Journal, where I published the results of my first research on secret patents ( IPJ 7 at 321-31), was a source of great encouragement to me at the start of this work, and I would also like to thank him for his advice during my search for a publisher, which eventually led me to Oxford University Press. There, the staff have all been most helpful, and particular thanks must go to the two anonymous reviewers who suggested numerous