It is, however, as the recorder of souls before Osiris that Thoth was important in the eyes of the Egyptian priesthood. He held this office because of his knowledge of letters and his gift of knowing what was right or in equilibrium. Again, he had the power of imparting the manner in which words should be correctly spoken. As has already been said, the mode of speech, the tone in which words were pronounced, spelt success or failure in both prayer and magical incantations. The secret of this Thoth taught to men, and this it was that the Egyptians especially desired to learn. Through the formula of Thoth the gates of the Duat were opened to the deceased, and he was safeguarded against its terrors. The _Book of the Dead_ was indeed believed to be the work of Thoth, as was the _Book of Breathings_, a much later work. The Greek writers upon things Egyptian imagined Thoth, whom they called Trismegistos, or Hermes the Thrice Great, as the prime source of all learning and wisdom. They ascribed to him the invention of the sciences of astronomy and astrology, mathematics, geometry, and medicine. The letters of the alphabet were also his invention, from which sprang the arts of reading and writing. According to them the 'Books of Thoth' were forty-two in number, and were divided into six classes, dealing with law and theology, the service of the gods, history, geography and writing, astronomy and astrology, religious writings and medicine. It is almost certain that most of this mass of material was the work of Alexandrian Greeks sophisticated by ancient Egyptian lore. Maāt