His fullest and most detailed work on chronology is entitled "De Temporum Ratione," and to this is added a chronicle of the world. On this elaborate work he was working down to A.D. 726. We have the authority of Ideler for saying that this is a complete guide to the calculation of times and festivals. He treats of the several divisions of time; and under the months, he speaks of the moon's orbit (c. xvii.), and its importance for the calendar, and the relation of the moon to the tides (c. xxix.); then of the equinoxes and solstices, the varying length of the days, the seasons of the year, the intercalary day, the cycle of nineteen years, the reckoning Anno Domini (c. xlvii.), indictions, epacts, the determination of Easter. All these things are taught with theoretical thoroughness, as well as also in their practical application. He also (c. lxv.) made a table for Easter from A.D. 532, "when Dionysius began the first cycle," to A.D. 1063.[66] This is followed by the "Chronicle or Six Ages of this World," altogether a work that was a growing nucleus, and went on expanding down to the invention of printing and the revival of classical literature.
But the works on which his eminence permanently rests, and by which he made all posterity indebted to him, are his historical and biographical writings. He wrote a poem on the miracles of St. Cuthbert, and afterwards he wrote a prose narrative "Of the Life and Miracles of St. Cuthbert, Bishop of Lindisfarne;" and in this, though a new and independent work, something of the poem is reproduced. It is in this prose work that we find the call of Cuthbert on the night of Aidan's death, the details of his hermit life on the rocky islet of Farne, to which he had retired for greater rigour of devotion, from which he was called back to be bishop at Lindisfarne, and to which after two years' episcopate he again retired for the remnant of his life.
He wrote also a prose life of St. Felix, drawing his materials from the metrical life of that saint in hexameters by Paulinus.
His greatest biographical work is "Lives of the Abbots of Wearmouth and Jarrow, namely, Benedict, Ceolfrid, Easterwini, Sigfrid, and Hwetbert." These were the heads of the two sister foundations with which his career was identified; and some of them had been his own teachers. The Life of Benedict is the most interesting, as might be expected, and it fills the largest part of the book.