Chapter XV has several forms, and each of them contains Hymns to Ra, which were sung daily in the morning and evening; specimen paragraphs are given above (pp. 33, 34). Chapter XVI is only a vignette that illustrates Chapter XV, Chapter XVII is a very important chapter, for it contains statements of divine doctrine as understood by the priests of Heliopolis. The opening words are, "I am Tem in rising. I am the Only One. I came into being in Nu (the Sky). I am Ra, who rose in primeval time, ruler of what he had made." Following this comes the question, "Who is this?" and the answer is, "It is Ra who rose in the city of Hensu, in primeval time, crowned as king. He existed on the height of the Dweller in Khemenu (i.e., Thoth of Hermopolis) before the pillars that support the sky were made." Chapter XVIII contains the Addresses to Thoth, who is entreated to make the deceased to be declared innocent before the gods of Heliopolis, Busiris, Latopolis, Mendes, Abydos, etc. These addresses formed a very powerful spell which was used by Horus, and when he recited it four times all his enemies were overthrown and cut to pieces. Chapters XIX and XX are variant forms of Chapter XVIII. Chapters XXI-XXIII secured the help of Thoth in "opening the mouth" of the deceased, whereby he obtained the power to breathe and think and drink and eat. Thoth recited spells over the gods whilst Ptah untied the bandages and Shu forced open their mouths with an iron (?) knife. Chapter XXIV gave to the deceased a knowledge of the "words of power" (hekau) which were used by the great god Tem-Khepera, and Chapter XXV restored to him his memory. Five chapters, XXVI-XXX, contain prayers and spells whereby the deceased obtained power over his heart and gained absolute possession of it. The most popular prayer is that of Chapter XXXB (see above, p. 4) which, according to its rubric, was "found," i.e., edited, by Herutataf, the son of the great Cheops, about 3600 B.C. This prayer was still in use in the early years of the Christian Era. In the Papyrus of Nu it is associated with Chapter LXIV, and the earliest form of it was probably in existence under the Ist dynasty.