How the Four-Color Conjecture Was Born

It takes time and effort to gain access and read manuscripts. The two letters containing the first mention of the 4CC are of high importance; yet, to the best of my knowledge, their complete facsimiles have never been published before. Selected transcriptions served a purpose, but, as we will see in Sect. 19.2, they contained certain shortcomings. In view of this, I am reproducing here, for the first time, the facsimile of De Morgan’s letter to Hamilton and the relevant fragment of Hamilton’s reply. Seeing – and reading – these letters allows us to immerse in the World Victorian. Analysis of these documents and the corrected transcription of De Morgan’s letter will follow. I am grateful to the Board of Trinity College Dublin, whose kind permission made reproducing these letters ([DeM1] and [Ham]) possible.