Penn's first public discussion was with Thomas Vincent, a London Presbyterian minister, who had reflected on the "damn able" doctrines of the Quakers. The discussion, which had turned chiefly upon the doctrine of the Trinity, ended uselessly, and Penn at once published The Sandy Foundation Shaken, a tract of ability sufficient to excite Pepys's astonishment, in which orthodox views were so offensively attacked that Penn was placed in the Tower, where he remained for nearly nine months. The imputations upon his opinions and good citizenship, made as well by Dissenters as by the Church, he repelled in Innocency with her Open Face, in which he asserts his full belief in the divinity of Christ, the atonement, and justification through faith, though insisting on the necessity of good works. He now published the most important of his books, No Cross, No Crown, which contained an able defence of the Quaker doctrines and practices, and a scathing attack on the loose and unchristian lives of the clergy. While completely refusing to recant Penn addressed a letter to Arlington in July 1669, in which, on grounds of religious freedom, he asked him to interfere. He was almost at once set at liberty.
An informal reconciliation now took place with his father, and Penn was again sent on family business to Ireland. At the desire of his father, whose health was fast failing, Penn returned to London in 1670. Having found the usual place of meeting in Gracechurch Street closed by soldiers, Penn, as a protest, preached to the people in the open street. With William Mead he was at once arrested and indicted at the Old Bailey on Sept. 1, for preaching to an unlawful, seditious and riotous assembly, which had met to gether with force and arms. The Conventicle Act not touching their case, the trial which followed, and which may be read at length in Penn's People's Ancient and Just Liberties Asserted, was a notable one in the history of trial by jury. With extreme courage and skill Penn exposed the illegality of the prosecution, while the jury, for the first time, asserted the right of juries to decide in opposition to the ruling of the court. They brought in a verdict declaring Penn and Mead "guilty of speaking in Grace church Street," but refused to add "to an unlawful assembly"; then, as the pressure upon them increased, they first acquitted Mead, while returning their original verdict upon Penn, and then, when that verdict was not admitted, returned their final answer "not guilty" for both. The court fined the jurymen 4o marks each for their contumacy, and, in default of payment, imprisoned them, whereupon they vindicated and established for ever the right they had claimed in an action (known as Bushell's case from the name of one of the jurymen) before the court of common pleas, when all twelve judges unanimously declared their imprisonment illegal.
Penn himself had been fined for not removing his hat in court, had been imprisoned on his refusal to pay, and had earnestly re quested his family not to pay for him. The fine, however, was
settled anonymously, and he was released in time to be present at his father's death on Sept. 16, 167o, at the early age of forty-nine. Penn now found himself in possession of a fortune of 11,500 a year, and a claim on the Crown for Li6,000, lent to Charles II. by his father. Upon his release Penn at once plunged into contro versy, challenging a Baptist minister named Jeremiah Ives, at High Wycombe, to a public dispute and, according to the Quaker account, easily defeating him. Hearing at Oxford that students who attended Friends' meeting were rigorously used, he wrote a vehement and abusive remonstrance to the vice-chancellor in de fence of religious freedom. This found still more remarkable expression in the Seasonable Caveat against Popery (Jan. 1671).
In the beginning of 1671 Penn was again arrested for preaching in Wheeler Street meeting-house by Sir J. Robinson, the lieutenant of the Tower, formerly lord mayor. Legal proof being wanting of any breach of the Conventicle Act, and the Oxford or Five Mile Act also proving inapplicable, Robinson, who had some special cause of enmity against Penn, urged upon him the oath of alle giance. This, of course, the Quaker would not take, and conse quently was imprisoned for six months. During this imprisonment Penn wrote several works, the most important being The Great Case of Liberty of Conscience (Feb. 1671), a noble defence of complete toleration. Upon his release he started upon a missionary journey through Holland and Germany; at Emden he founded a Quaker society, and established an intimate friendship with the princess palatine Elizabeth.
Upon his return home in the spring of 1672 Penn married Gul ielma Springett, daughter of Mary Pennington by her first hus band, Sir William Springett. She appears to have been equally remarkable for beauty, devotion to her husband, and firmness to the religious principles which she had adopted when little more than a child. Penn now settled at Rickmansworth, Hertfordshire, and gave himself up to controversial writing. To this year, 1672, belong the Treatise on Oaths and England's Present Interest Considered. In the year 1673 Penn secured the release of George Fox, addressed the Quakers in Holland and Germany, carried on public controversies with Thomas Hicks, a Baptist, and John Faldo, an Independent, and published his treatise on the Christian Quaker and his Divine Testimony Vindicated, the Discourse of the General Rule of Faith and Practice, Reasons against Railing (in answer to Hicks), Counterfeit Christianity Detected, and a Just Rebuke to One-and-twenty Learned Divines (an answer to Faldo and to the publication entitled Quakerism no Christianity). His last public controversy was in 1675 with Richard Baxter, in which, of course, each party claimed the victory.