Of genius or demon, we have already spoken in the article on "angel." It is not easy to know precisely whether the peris of the Persians were invented before the demons of the Greeks, but it is very probable that they were. It may be, that the souls of the dead, called shades, manes, etc., passed for demons. Hesiod makes Hercules say that a demon dictated his labors.
The demon of Socrates had so great a reputation, that Apuleius, the author of the "Golden Ass," who was himself a magician of good repute, says in his "Treatise on the Genius of Socrates," that a man must be without religion who denies it. You see that Apuleius reasons precisely like brothers Garasse and Bertier: "You do not believe that which I believe; you are therefore without religion." And the Jansenists have said as much of brother Bertier, as well as of all the world except themselves. "These demons," says the very religious and filthy Apuleius, "are intermediate powers between ether and our lower region. They live in our atmosphere, and bear our prayers and merits to the gods. They treat of succors and benefits, as interpreters and ambassadors. Plato says, that it is by their ministry that revelations, presages, and the miracles of magicians, are effected."--"_Cæterum sunt quædam divinæ mediæ potestates, inter summum æthera, et infimas terras, in isto intersitæ æris spatio, per quas et desideria nostra et merita ad deos commeant. Hos Græco nomine demonias nuncupant. Inter terricolas cœli colasque victores, hinc pecum, inde donorum: qui ultro citroque portant, hinc petitiones, inde suppetias: ceu quidam utriusque interpretes, et salutigeri. Per hos eosdem, ut Plato in symposio autumat, cuncta denuntiata; et majorum varia miracula, omnesque præsagium species reguntur._"
St. Augustine has condescended to refute Apuleius in these words:
"It is impossible for us to say that demons are neither mortal nor eternal, for all that has life, either lives eternally, or loses the breath of life by death; and Apuleius has said, that as to time, the demons are eternal. What then remains, but that demons hold a medium situation, and have one quality higher and another lower than mankind; and as, of these two things, eternity is the only higher thing which they exclusively possess, to complete the allotted medium, what must be the lower, if not misery?" This is powerful reasoning!