In the mean time a pope was elected, to whom we owe the production of the 'Opus Majus.' This was Clement IV. (elected 1265), who had previously, when cardinal-bishop of Sabina, been legate in England. Here he had heard of Bacon's discoveries, and earnestly desired to see his writings; but, as before stated, the prohibition of the Franciscans prevented his wish being complied with. After his election as head of the Church, Bacon, conceiving that there would be no danger nor impropriety in disobeying his immediate superiors at the command of the pope, wrote to him, stating that he was now ready to send him whatever he wished for. The answer was a repetition of the former request; and Bacon accordingly drew up the 'Opus Majus,' of which it may be presumed he had the materials ready. It appears that he had mentioned the circumstances in which he stood; for Clement's answer requires him to send the work with haste, any command of his superiors or constitution of his order notwithstanding, and also to point out, with all secrecy, how the danger mentioned by him might be avoided. The book was sent in the year 1267, by the hands of John of London, a pupil of whom he speaks highly, and who has usually obtained some notice from the very great praise which Bacon in one place appears to give him, when he says that he only knows two good mathematicians, one of whom he calls John of London. But from some other circumstances Dr. Jebb concludes, with great probability, that this John was not the pupil above mentioned, but John Peccam, a London Franciscan, afterwards Archbishop of Canterbury, who was well known as a mathematician, and whose treatise on Optics, 'Perspectivae communis libri tres,' was printed at least six times between 1542 and 1627, at Nuremberg, Venice, Paris, and Cologne. Before the 'Opus Majus,' Bacon, according to his own account, had written nothing except a few slight treatises, "capitula quaedam." Before he took the vows he wrote nothing whatever; and afterwards, as he says to Clement, he would have composed many books for his brother and his friends, but when he despaired of ever being able to communicate them, he neglected to write.