1. Autograph letter signed ("Morpeth") from William George Howard, 8th Earl of Carlisle to Leonard Horner, dated 30 June 1840, Castle Howard [North Yorkshire]: "I am afraid my answer cannot be quite as definite as you might wish. My Father does not seem to remember very well whether he wrote the inscription entirely, but he says he certainly was concerned in the composition, which may have been arranged with other co-adjutors at Holland House [...]".

2. Autograph letter signed from William George Howard, 8th Earl of Carlisle to Sir Charles Lyell, dated 10 January 1851, Castle Howard [North Yorkshire]: "I return your enclosures with many thanks. Mr Ticknor’s letter is very interesting and suggestive. I add another enclosure of my own, if you or L[ad]y Lyell would accept it from me, though I apprehend you will both think I take a more conscious view than I need have done".