Writing in 1939, the historian of mathematics Herbert Turnbull described John Pell as 'a mysterious figure' and commented: 'he may well prove to be an unsuspected genius, for his manuscripts appear to survive, unexamined, in the British Museum.' Turnbull's expectations were pitched a little too high: although Pell was a man of unusual intellectual abilities, and one of the leading mathematicians of his day, his work does not merit any use of the term...