At first he completed the drama in three acts. It was not till several months after, when at Florence, that he conceived that a fourth act, a sort of hymn of rejoicing in the fulfilment of the prophecies with regard to Prometheus, ought to be added to complete the composition. The prominent feature of Shelley's theory of the destiny of the human species was that evil is not inherent in the system of the creation, but an accident that might be expelled. This also forms a portion of Christianity: God made earth and man perfect, till he, by his fall, 'Brought death into the world and all our woe.' Shelley believed that mankind had only to will that there should be no evil, and there would be none. It is not my part in these Notes to notice the arguments that have been urged against this opinion, but to mention the fact that he entertained it, and was indeed attached to it with fervent enthusiasm. That man could be so perfectionized as to be able to expel evil from his own nature, and from the greater part of the creation, was the cardinal point of his system. And the subject he loved best to dwell on was the image of One warring with the Evil Principle, oppressed not only by it, but by all--even the good, who were deluded into considering evil a necessary portion of humanity; a victim full of fortitude and hope and the spirit of triumph emanating from a reliance in the ultimate omnipotence of Good. Such he had depicted in his last poem, when he made Laon the enemy and the victim of tyrants. He now took a more idealized image of the same subject. He followed certain classical authorities in figuring Saturn as the good principle, Jupiter the usurping evil one, and Prometheus as the regenerator, who, unable to bring mankind back to primitive innocence, used knowledge as a weapon to defeat evil, by leading mankind, beyond the state wherein they are sinless through ignorance, to that in which they are virtuous through wisdom. Jupiter punished the temerity of the Titan by chaining him to a rock of Caucasus, and causing a vulture to devour his still-renewed heart. There was a prophecy afloat in heaven portending the fall of Jove, the secret of averting which was known only to Prometheus; and the god offered freedom from torture on condition of its being communicated to him. According to the mythological story, this referred to the offspring of Thetis, who was destined to be greater than his father. Prometheus at last bought pardon for his crime of enriching mankind with his gifts, by revealing the prophecy. Hercules killed the vulture, and set him free; and Thetis was married to Peleus, the father of Achilles.