The dialogue is conducted by three persons, Salviati, Sagredo, and Simplicio. Salviati, who is the true philosopher in the dialogue, was the real name of a nobleman whom we have already had occasion to mention. Sagredo, the name of another noble friend of Galileo's, performs a secondary part under Salviati. He proposes doubts, suggests difficulties, and enlivens the gravity of the dialogue with his wit and pleasantry. Simplicio is a resolute follower of Ptolemy and Aristotle, and with a proper degree of candour and modesty, he brings forward all the common arguments in favour of the Ptolemaic system. Between the wit of Sagredo, and the powerful philosophy of Salviati, the peripatetic sage is baffled in every discussion; and there can be no doubt that Galileo aimed a more fatal blow at the Ptolemaic system by this mode of discussing it, than if he had endeavoured to overturn it by direct arguments. The influence of this work on the public mind was such as might have been anticipated. The obnoxious doctrines which it upheld were eagerly received, and widely disseminated; and the church of Rome became sensible of the shock which was thus given to its intellectual supremacy. Pope Urban VIII., attached though he had been to Galileo, never once hesitated respecting the line of conduct which he felt himself bound to pursue. His mind was, nevertheless, agitated with conflicting sentiments. He entertained a sincere affection for science and literature, and yet he was placed in the position of their enemy. He had been the personal friend of Galileo, and yet his duty compelled him to become his accuser. Embarrassing as these feelings were, other considerations contributed to soothe him. He had, in his capacity of a cardinal, opposed the first persecution of Galileo. He had, since his elevation to the pontificate, traced an open path for the march of Galileo's discoveries; and he had finally endeavoured to bind the recusant philosopher by the chains of kindness and gratitude. All these means, however, had proved abortive, and he was now called upon to support the doctrine which he had subscribed, and administer the law of which he was the guardian.