I once remarked to him that his mind was a wonder to me; that impressions were easily made upon it and never effaced. ‘No,’ said he, ‘you are mistaken; I am slow to learn, and slow to forget that which I have learned. My mind is like a piece of steel-very hard to scratch anything on it, and almost impossible after you get it there to rub it out.’ I give this as his own illustration of the character of his mental faculties; it is as good as any I have seen from anyone.
Douglas L. Wilson and Rodney O. Davis, editor, Herndon’s Informants, p. 499 (Letter of Joshua F. Speed to William H. Herndon, December 6, 1866). Herndon-313-04 ，Ludwig-136-13