Adam Schall von Bell, the Jesuit Director of Beijing Observatory and Head of the Mathematical Board, in his work in astronomy. Unfortunately for them, the political situation shifted dramatically in 1661, on the death of the young Shunzhi Emperor, aged 23. His son and successor, Xuanye (the Kangxi Emperor), was only 7, so the government was placed in the hands of four regents. Unlike Shunzhi, the regents were not in favour of the Jesuits, who suffered increased persecution as a result. Astronomy contests In 1664, the Chinese astronomer Yang Guangxian (1597–1669), who had published a pamphlet against the Jesuits, challenged Schall von Bell to a public astronomy competition. Yang won and took Schall von Bell's place as Head of Mathematics. Having lost the competition, Schall von Bell and the other Jesuits were chained and thrown into a filthy prison, accused of teaching a false religion. They were bound to wooden pegs in such a way that they could neither stand nor sit and remained there for almost two months until a sentence of strangulation was imposed. A high court found the sentence too light and ordered them to be cut up into bits while still alive. Fortunately for them, on 16 April 1665, a violent earthquake destroyed the part of the prison chosen for the execution. An extraordinary meteor was seen in the sky, and a fire destroyed the part of the imperial palace where the condemnation was pronounced. This was seen as an omen and all the prisoners were released. However, they still had to stand trial, and all the Jesuits but Verbiest, Schall von Bell and two others were exiled to Canton. Schall von Bell died within a year, due to the conditions of his confinement. In 1669, the Kangxi Emperor managed to take power by having the remaining (corrupt) regent, Oboi, arrested. In the same year, the emperor was informed that serious errors had been found in the calendar for 1670, which had been drawn up by Yang Guangxian. Kangxi commanded a public test to compare the merits of European and Chinese astronomy. The test was to predict three things: the length of the shadow thrown by a gnomon of a given height at noon of a certain day; the absolute and relative positions of the Sun and the planets on a given date; and the exact time of an anticipated lunar eclipse. It was decided that