Toward the end of the sixteenth century the necessity for the correction of the calendar became more urgently manifest and Pope Gregory XIII invited Father Clavius, S.J., to take up the subject. At this time also, as is described by Pope Leo XIII in his Motu Proprio of 1891, “Gregory XIII [nearly half a century before the condemnation of Galileo] ordered a tower to be erected in a convenient part of the Vatican buildings and to be fitted out with the greatest and best instruments of the time. There he held the meetings of the learned men to whom the reform of the calendar had been entrusted. The tower stands to this day a witness to the munificence of its founder. It contains a meridian line by Ignazio Danti of Perugia, with a round marble plate in the centre, adorned with scientific designs. When touched by the rays of the sun that are allowed to enter from above, the designs demonstrate the error of the old reckoning and the correctness of the reform.” It was evidently the intention of the Pope that there should be, as a permanent institution in Rome, an astronomical observatory fully equipped and supported by the revenues of the Holy See and with a prominent scientist at its head. This purpose has been constantly kept in mind by the Popes ever since, though not long after Gregory’s time, but not at all because of any opposition to science, the observatory founded by him came for more than a century not to be used for the purpose intended because its place was supplied by another Roman institution directly under the patronage of the Popes.
This was the Roman College, the great central school of the Jesuits, in the capital of Christendom. That Order was scarcely fifty years in existence in Pope Gregory XIII’s time, yet it was to a member of it that the Pope turned for expert scientific direction in the correction of the calendar. During the next three centuries science as patronized by the Popes in Rome was mainly in the hands of the Jesuits. When it is recalled that this Order is directly under the control of the Pope, the professed members taking a special vow of obedience to him, it will be understood that the Jesuit policy with regard to science must be taken as representing the Papal position in its regard. If it is further recalled that Poggendorff in his Biographical Lexicon of Men Eminent in Science gives the names of some 500 Jesuits, though the Order was not in a position to do any work in science until 1550, it will be readily appreciated that the Popes acted wisely to encourage an institute so prolific in eminent scientists in its scientific work at the Roman College, rather than maintain a separate scientific department at the Vatican.
James J. Walsh, The Popes and Science (1908)