John Erroll is curator of the John M. Mossman Lock Collection, at the General Society of Mechanics and Tradesmen in New York City. His son, David Erroll , is an attorney. Anne Day is a photographer whose most recent work appeared in the book The United States Capitol: Its Architecture and Decoration. This article is adapted from their book American Genius: Nineteenth-Century Bank Locks and Time Locks, which is being published in October by the Quantuck Lane Press.