Thomas Harriot’s Papers on the Calendar

Abstract

Among the Petworth House manuscripts of Thomas Harriot, formerly with MS 241 but now separately bound, are twenty pages on calendrical chronological matters. Although they are by no means the most original of his works they do help to fill out the picture we have of a man who occupied a key position in early seventeenth-century science. An edition of them is appended to the present chapter. The papers are disordered: some of them refer back to the turn of the century, but most seem to have been put together around 1615 or 1616. The first dozen pages form a coherent little tract on the determination of Easter, seemingly intended for a popular audience, and beginning with rules as clearly set out as any you will find in comparable works aimed at those who are able to compute without recourse to counting on the joints of the hand. A thirteenth page is a fair copy of earlier material, and I do not think that it is of Harriot’s writing. The last pages show Harriot’s concern with the date hour of the creation of the world, and with the real date of Christ’s birth — a perennial problem for the Christian chronologist who was conscious of the errors in the Dionysian reckoning in common use. Harriot records inconsistencies as between the Roman and Alexandrian reckoning of Easter in the early centuries of Christian reckoning. Inevitably he introduces astronomical material concerning solar and lunar motions, but here it is always of an elementary character, and the later pages are more interesting for the gleams of light they throw on his historical sources.