The Chinese calendar was entrusted to official astronomers in the “Board of Mathematics”, composed of 200 members in this board, and divided into several sections. It was their duty to make known in advance the astronomical situation for the whole year, the days of new and full moons, movements of the sun with the dates of its entrance into each of the twenty-eight constellations forming the Chinese zodiac, the times of the solstices and equinoxes, and the beginnings of seasons, the positions and conjunctions of planets, finally, and especially, eclipses of the moon and the sun. For these announcements the Chinese had several empirical rules, inherited from their ancestors, and especially those which the Muslim astronomers had brought to China during the Yuen, or Mongol dynasty. These rules were insufficient to prevent errors and sometimes serious faults, and, having no scientific principle, the Chinese astronomers were incapable of discovering the defects of their methods and calculations, far less correcting them. Already Father Matteo Ricci SJ – the founder of the mission – had seen that this was a unique opportunity for the missionaries to render a service and thus to strengthen their position in China. Father Johann Adam Schall von Bell (1592-1666) who had entered the Jesuits in 1611 and arrived in China in 1619, was called in 1630 to Bejing to work as an astronomer on the reform of the Chinese calendar.
Together with Father Giacomo Rho (1593 – 1638), Father Schall undertook the difficult task to train the Board of Mathematics in astronomy, arithmetic, geometry, and other parts of mathematics, despite of superstitious concerns for tradition and jealousy towards the European experts. In 1638, the reform had become law and needed only to be put into execution. All the provinces of China were soon informed of the important commission of reforming the calendar which had been entrusted to the missionaries. The news created a great sensation which benefited the whole mission. Everywhere the preaching of the Gospel was allowed unprecedented liberty. Father Schall profited by this, directing his apostolic especially to persons in the imperial palace; this led to the conversion of ten eunuchs, among whom were the sovereign’s most qualified servants.
New trouble came for Father Schall: he accepted after some hesitation to become the Director of the Board of Mathematics, since there was no other person capable for this job. This title was linked to the title of a Mandarin, a title of honour that he refused several times, “even on his knees before the Tribunal of Rites”; he only finally accepted it when his superior told him so and renouncing all financial benefits. Nonetheless, two questions were brought forward to the Pope: Can a priest be a mandarin since this constitutes a public office and violates canon law? And the second was even more serious: the Chinese calendar contained indications on lucky and unlucky days and other signs of superstitions. The second could be cleared completely, because given the complicated bureaucracy, Father Schall and his office only gave the astronomical data and had no influence whatsoever on the final edition of the calendar. Importantly for setting at rest Father Schall’s conscience, Pope Alexander VII declared in 1664 that the Jesuits of China were allowed “to exercise the office and dignity of mandarin and imperial mathematician”.
In November 1664, follwing the death of emperor Shan chih, Father Schall and the other missionaries residing at Peking were loaded with chains and thrown into prison. They were accused of high treason and of propagation of an “evil religion”. Father Schall had suffered a stroke and could not speak himself, and Father Verbiest took his defense. Nonetheless, on 15 April 1665, Father Schall was sentenced to death. Almost immediately afterwards a violent earthquake was felt at Peking, a thick darkness covered the city, a meteor of strange aspect appeared in the heavens, and fire reduced to ashes the part of the imperial palace where the sentence was delivered. The superstitious Tatars and Chinese were terrified – the missionaries and the Christians will have seen God’s divine providence! – , and, in consequence, the death sentence was revoked on 02 May 1665. Father Schall could return to his church with his fellow missionaries. He survived these trials a year, dying at the age of seventy-five, having consecrated forty-five years to the Chinese missions. Peace was not entirely restored to the Christian communities until 1669, when the young emperor K’ang-hi’ assumed government, declared the sentence against Father Schall void and iniquitous and to ordered solemn funeral ceremonies in his honour. More than 20 years later the same emperor – not least in consideration of the friend and teacher of his father – enacted the edict on freedom of 22 March 1692, which gave Christianity in China the status of a state-recognized religion and the same rights as Buddhists and Taoists. At the End of the 17th century, there were 200 communities in whole China with around 150.000 Christians.