The two histories and the "Life of William Pitt" were considered of great importance on account of Stanhope's unique access to manuscript authorities on Pitt the Elder's life. His records of the Duke of Wellington's remarks during his frequent visits were also considered of great use to the historian as a substitute for Wellington's never-written memoirs. They were secretly transcribed because of Wellington's famous antagonism to the "truth" of recollected history. He also edited the letters that his distant cousin, Philip Stanhope, 4th Earl of Chesterfield, had written to his natural son, Philip. They were published between 1845 and 1853.