Rothgar collects automata. Read more about them here.
Browse through various pictures of settings for the books
A wonderful online exhibit about Queen Charlotte, including pictures of her and King George, who depended on Rothgar for advice
Information about George III
outline of politics and chief characters of the period
Poems of the period
Information about the justice system in the 18th century
Views of the Yorkshire Dales
A little about Johanne Christian Bach, a bit player in Devilish
Information and pictures about the Chevalier D'Eon, who tangles with Rothgar in Devilish, to his cost. (In French but the pictures are good anyway.)