1. Contemporary registers, chronicles, and other documents, either now, or known to have been originally, in a manuscript form. 2. Inscriptions on monuments and coins. Such, for example, are the inscriptions on the monuments of Egypt and on the buried ruins of Nineveh and Babylon. Such are the ancient epitaphs, heathen and Christian, in the Roman catacombs. The study of ancient inscriptions of various sorts has thrown much light of late upon Grecian and Roman antiquity. 3. The entire literature of a people, in which its intellectual, moral, and social condition, at any particular era, is mirrored. 4. Material structures of every kind, as altars, tombs, private dwellings,--as those uncovered at Pompeii,--public edifices, civil and religious, paintings, weapons, household utensils. These all tell a story relative to the knowledge and taste, the occupations and domestic habits, and the religion, of a past generation or of an extinct people. 5 Language is a memorial of the past, of the more value since it is not the product of deliberate contrivance. _Comparative philology_, following languages back to their earlier stages and to the parent stocks, unveils the condition of society at remote epochs. It not only describes the origin of nations, but teaches something respecting their primitive state. 6. Histories written at former periods, but subsequently to the events described in them, are a secondary but valuable source of historical knowledge. This is especially true when their authors had access to traditions that were nearer their fountain, or to literary monuments which have perished. HISTORICAL CRITICISM.--Historical scholars are much more exacting as regards evidence than was formerly the case. The criticism of what purports to be proof is more searching. At the same time, what is called "historical divination" can not be altogether excluded. Learned and sagacious scholars have conjectured the existence of facts, where a gap in recorded history--"the logic of events"--seemed to presuppose them; and later discoveries have verified the guess. This is analogous to the success of Leverrier and Adams in inferring the existence of an unknown planet, which the telescope afterwards discovered. An example of historical divination on a large scale is furnished by the theories of the great German historian, _Niebuhr_, in respect to early Roman history. He propounded opinions, however, which in many particulars fail to obtain general assent at present.