"To tell the truth simply, openly, without reservation, is the unimpeachable first principle of all right dealing; and historians have no license to be quit of it. Unquestionably they must tell us the truth, or else get themselves enrolled among a very undesirable class of persons . . . But the thing is by no means so easy as it looks. The truth of history is a very complex and very occult matter. It consists of things which are invisible as well as of things which are visible."