Dynasties of Gods.--In the history of Egyptian religion one set of such gods succeeds another as the prevailing dynasty, according as the seat of empire in the country shifts to a new nome. These religious changes could take place without great convulsions. It was only the attempt to extinguish old established worships that was fiercely resisted, not the addition of a new god, even as superior to those already seated in the temple. In the earliest times known to us Ra of Heliopolis is the chief god of Egypt; Osiris of Thinis (Abydos) is also a great god, but the most characteristic development of Osiris-worship belongs to a later period. Ptah of Memphis comes to the front in the earliest dynasties. Much later is the rise of Amon to the first place, which he held when the Greeks and Romans had to do with Egypt. A very short account only can be given of the sets of gods of which these are the heads. Ra.--Ra means "sun"; his seat is Heliopolis or "On," where Joseph's master Potiphera, or "Priest of Ra," lived. Heliopolis is the "house of the obelisk," the obelisk being a representation of the sun. First a kindly old king, he is later a warrior; he has to contend with the serpent Apep, the dragon of darkness who appears pierced by the shafts of Ra. But as Ra sinks in the conflict he is comforted by Hathor, the goddess of the western sky, and avenged by Horus, the ever young and ever victorious winged sun.[5] But Ra is a god of the under as well as the upper world. King Pi'anchi, of the twenty-second dynasty, entered into the great temple of Ra at Heliopolis and penetrated to the inmost chamber of it, afterwards sealing it up again. We are told what he saw there.[6] He looked upon "his father Ra," and saw the two boats intended for the daily journey of the god. Ra travels in his boat through the sky, but also at night through the under-world, of which also he is lord. The progress of the god of light through the world of darkness is a theme which was worked out later in much detail in connection with Osiris; but it forms part of the earliest known religious conceptions of the Egyptians, and Ra's voyage through the "Am Duat" or under-world, is described in considerable detail. Many figures accompany him in this voyage, and many are the obstacles to be overcome during the successive hours of night before he reaches again the gates of day. The souls of men who have died are also led by him through those nether spaces; by a hidden knowledge, if they have been at pains to possess themselves of it, they are able to keep close to Ra on the perilous journey. He gives them fields to cultivate in the plains beneath, and they are made glad by his appearance at the appointed hour in the nights that follow.