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John Jay to Charles Thomson

February 29, 1780

During the Revolutionary War, it was common for correspondence to be intercepted numerous methods measures were developed to communicate in secret. John Jay, as Secretary for Foreign Affairs, was particularly concerned about his correspondence being intercepted. He developed several codes over the years, some specifically for personal correspondence, some for correspondence with Congress, and others for correspondence related to the war. The code he purposed on February 29, 1780 was a short lived one which was replaced just a few years later.

In this letter to Charles Thomson, he wrote "I purpose the following cypher...Use the second part of Boyer’s Dictionary where the English is placed before the French – it is not paged – you will therefore number the pages beginning with page – Letter A and so on regularly [when you work add five to the number of the page]. There are three columns – distinguish them – a under the first figures denotes the first, a under the second, the second, and a under the third, the third. Count the words from the bottom including the one you use and to the amount add 10…The dictionary I have is the thirteenth edition and was printed in London in the year 1771…"

Charles Thompson responded in 1780 (View Letter)

Charles Thomson to John Jay, 7 June 1780, John Jay Papers, Rare Book & Manuscript Library, Columbia University in the City of New York