make a collection of the chief privileges of the Roman Church. This collection, whose value is acknowledged by all the annalists, is still preserved in the Vatican archives. In the preface Platina not only avoids any antagonism towards the Church but even refers with approbation to the punishing of heretics and schismatics by the popes, which is the best proof that Sixtus IV, by his marks of favour, had won Platina for the interests of the Church. Besides his principal work Platina wrote several others of smaller importance, notably: . The Pinacoteca Vaticana contains a famous fresco by Melozzo da Forlì representing Sixtus IV Appointing Platina as Prefect of the Vatican Library. Halley's comet As a paragraph from Platina's Vitæ Pontificum first gave rise to the legend of the excommunication of Halley's comet by Pope Callixtus III, we here give the legend briefly, after recalling some historical facts. After the fall of Constantinople (1453), Nicolas V appealed in vain to the Christian princes for a crusade. Callixtus III (1455–1458), immediately after his succession, sent legates to the various courts for the same purpose; and, meeting with no response, promulgated a bull June 29, 1456, prescribing the following: all priests were to say during Mass the oratio contra paganos; daily, between noon and vespers, at the ringing of a bell, everybody had to say three Our Fathers and Hail Marys; processions were to be held by the clergy and the faithful on the first Sunday of each month, and the priests were to preach on faith, patience, and penance; to expose the cruelty of the Turks, and urge all to pray for their deliverance. The first Sunday of July (July 4), the first processions were held in Rome. On the same day the Turks began to besiege Belgrade. On July 14 the Christians gained a small advantage, and on the twenty-first and twenty-second the Turks were put to flight. In the same year Halley's comet appeared. In Italy it was first seen in June. Towards the end of the month it was still visible for three hours after sunset, causing great excitement everywhere by its extraordinary splendour. It naturally attracted the attention of astrologers as may appear from the long judicium astrologicum by Avogario, of Ferrara, dated June 17, 1467; it was found again by Celoria among the manuscripts of Paolo Toscanelli, who had copied it himself. The comet was seen