INTRODUCTION

The Science of Time-Reckoning original: Computus¹ is the science by which time is reckoned, either by the movements of the heavenly bodies or by human authority, and is thus either natural or by authority. Bacon’s definition will be found on p. 2, Grosseteste’s Robert Grosseteste (c. 1175–1253), an influential English philosopher and scientist who served as Bishop of Lincoln. on p. 216, and Alexander de Villa Dei’s A French author (c. 1175–1240) known for writing the "Massa Compoti," a popular verse textbook on time-reckoning. on p. 268.

The need for a Science of Time-Reckoning arises from the difficulty of combining a calendar based on the movements of the moon with the use of a solar year, since the day, the lunar month, and the solar year are incommensurable—that is, no number of days will ever make an exact number of lunar months or solar years, and no number of lunar months will make an exact number of years. Any calendar must therefore be a compromise.

The Jewish Calendar is based on lunar months and a solar year, inserting an intercalary month An extra month added to the calendar periodically to ensure that seasonal festivals remain in their proper solar seasons. when the difference of ten and seven-eighths days between twelve lunar months and a solar year has amounted to another month; the European Calendar is based on the old Roman one and is entirely solar, the months having no relation to the moon. Owing, however, to the definition of Easter adopted in the general practice of Christianity, the Church Calendar still depends on the movements of a hypothetical satellite—the ecclesiastical moon A calculated, mathematical moon used by the Church to determine the date of Easter, which often differs slightly from the actual astronomical moon.—which in the Middle Ages bore a rather distant relationship to the moon of the heavens, though in the reformed calendar the relation is designedly close.

The Christian year seems, in the first centuries of the Church’s history, to have been marked by anniversary feasts and fasts. Some of these, like the feast of the Nativity, were observed on fixed dates, but the time for keeping the most important, that of Easter, was not settled for some time. It seems possible that in the early Church the Easter festival original: Pascha was rather the feast of the Sacrifice than of the Resurrection of Christ, which was regarded by Saint Paul as the first-fruits to be offered, according to Jewish law, on the day after the Sabbath. The Christian Easter festival was celebrated on the Sunday of

¹ The spelling Computus is followed when the word is used as English. In Latin the spelling of the author is followed.