It is very true that I have said that I considered Napoleon's presence in the field equal to forty thousand men in the balance. This is a very loose way of talking; but the idea is a very different one from that of his presence at a battle being equal to a reinforcement of forty thousand men.
Notes for September 18, 1836. "Notes of Conversations with the Duke of Wellington, 1831-1851". Book by Earl Philip Henry Stanhope Stanhope, 1886.
