"I will show your letter to Duval, by way of justification for not answering his challenge; and I think he must allow the validity of it; for a frozen brain is as unfit to answer a challenge in poetry, as a blunt sword is for a single combat."
— Stanhope, Philip Dormer, fourth earl of Chesterfield (1694-1773)
(II.cxliii, pp. 133-4, LONDON, January 24, O. S. 1749.)
Reading David Roberts' edition of Lord Chesterfield's Letters (Oxford: OUP, 1998); and searching text from Project Gutenberg <Link>
Consulting and citing, where possible, Letters Written by the late Right Honourable Philip Dormer Stanhope, Earl of Chesterfield, to his son, Philip Stanhope, Esq. (London: Printed for J. Dodsley, 1774). <Link to ECCO>
See also Miscellaneous Works of the late Philip Dormer Stanhope, Earl of Chesterfield: Consisting of letters to his Friends, never before printed, and Various Other Articles. 2 vols. (London: Printed for Edward and Charles Dilly, 1777). <Link to ECCO>