On 12 May 1726, the Reverend Ezekiel Hamilton wrote a letter from Madrid to John Hay, Earl of Inverness in Rome.1 Hamilton principally wanted ‘to send … the cypher I had so long promised’. Evidently Hamilton was a valued Jacobite cryptographer . However, fortunately for historians, Hamilton’s explanation regarding the cypher is written in plain English:

is putts me in mind of another view I had in compiling this cypher, and that is to make it chie y a military one, and calculated as much as possible for a fair meeting on the green (a health I have o en drank but a thing I long extremely to see). For I shou’d have been altogether unworthy of the military Title His Majesty has been pleas’d to Honour me with, if I had not perfected the cypher on this Head; and as the aforesaid Meeting at Home is the end of all negotiations and correspondence abroad, any cypher that is not contriv’d chie y for an Invasion is in my Humble opinion Literally a cypher and can never make a signi cant Figure.2