addressed the problem of finding the circumference of a circle knowing its diameter.
Gregory (or his translator) did not use the word pi or the Greek character π in this context, referring instead to the work of the 17th-century Dutch mathematician Ludolf van Ceulen establishing the quantity with much greater precision than our shorthand approximation to two decimal places (3.14). (The passage in question used a rather odd Latinized form of van Ceulen's first name). Special Collections also holds an 18th-century edition of van Ceulen's work.
In a foldout plate in his Geometrical and graphical essays of 1791,
the instrument-maker George Adams (1750-1795) included diagrams of polygons inscribed in a circle or circumscribing it:
Thanks to Anthony Lattis for zeroing in on Gregory's and Adams' treatments of π.