Peter Heylyn's Cosmographie
Published in 1652, Peter Heylyn's Cosmographie presents readers with a universal geography in four books, one of which touches on the Prester John legend.
Most significantly, Cosmographie doubts Prester John's dual function as priest and king, which may not be surprising given the anti-Catholic sentiments of its author. Brewer (p. 239) also notes that Heylyn dismisses a circulating notion (proposed by Scaliger) that Ethiopians originally descended from Asia. Heylyn instead offers an account of an Asian Prester John and reasons that the Portuguese identification of John with Ethiopia resulted merely from linguistic misunderstanding.
Brooks (p. 167-8) excerpts Heylyn's description of the nature of Prester John's name and title:
And yet I more incline to those, who finding that the word Prestegan signifieth an Apostle, in the Persian tongue, and Prestigani, and Apostolical man: do thereupon inferr that the title of Padescha Prestigiani, and Apostolick King, was given unto him for the Orthodoxie of his belief, which not being understood by some, instead of Preste-gian, they have made Priest-John, in Latine Presbyter Johannes; as by a like mistake, one Pregent (or Prægian as the French pronounce it) commander of some Gallies under Lewis the 12, was by the English of those times called Prior John.