Lass, R. 1999. The Cambridge History of the English Language, Vol III.
Paston letters on Archive.org – https://archive.org/details/pastonlet…
Hart, J. 1569. An Orthographie.
Butler, C. 1633. English Grammar.
Brilioth, B. 1913. A Grammar of the Dialect of Lorton (Cumberland).
Wheeler, A. 1790. The Westmorland Dialect in Three Familiar Dialogues.
Warren Maguire’s fantastic mapping of some of the findings of Alexander Ellis’s 1889 survey: http://www.lel.ed.ac.uk/EllisAtlas/Vo…
msamba 
When I was in Scotland in the early seventies, they still had this “gh” sound in Glasgow. The sentence “A fine bright moonlight night tonight” would become “A braw brecht moonlecht necht tenecht”. (The “ch” pronounced like in German “nicht”.)
I just today heard an interview with the late George Harrison, and he would pronounce the “g” in “sing” and “singing”. So that must be (have been) part of the Liverpool dialect.
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