He might then set about teaching us from his own writings a mental resource, far superior to any similar device practised by ourselves, by which the day of the week belonging to any day of the month, in any year of the Christian era, might easily and speedily be found.
And when the few, who would give themselves the trouble of thoroughly understanding it, came to perceive its easiness of acquirement, its simplicity in practice, and its firm hold upon the memory, they might well marvel how so admirable a facility should have been so entirely forgotten, or by what perversion of judgment it could have been superseded by the comparatively clumsy and impracticable method of the Dominical letters.
Let us hear his description of it in his own words:
"Simile autem huic tradunt argumentum ad inveniendam diem Calendarum promptissimum.
"Habet ergo regulares Januarius II, Februarius V, Martius V, Apriles I, Maius III, Junius VI, Julius I, Augustus IIII, September VII, October II, November V, December VII. Qui videlicet regulares hoc specialiter indicant, quota sit feria per Calendas, eo anno quo septem concurrentes adscripti sunt dies: cæteris vero annis addes concurrentes quotquot in præsenti fuerunt adnotati ad regulares mensium singulorum, et ita diem calendarum sine errore semper invenies. Hoc tantum memor esto, ut cum imminente anno bisextili unus concurrentium intermittendus est dies, eo tamen numero quem intermissurus es in Januario Februarioque utaris: ac in calendis primum Martiis per illum qui circulo centinetur solis computare incipias. Cum ergo diem calendarum, verbi gratia, Januarium, quærere vis; dicis Januarius II, adde concurrentes septimanæ dies qui fuerunt anno quo computas, utpote III, fiunt quinque; quinta feria intrant calendæ Januariæ. Item anno qui sex habet concurrentes, sume v regulares mensis Martii, adde concurrentes sex, fiunt undecim, tolle septem, remanent quatuor, quarta feria sunt Calendæ Martiæ."--Bedæ Venerabilis, _De Temporum Ratione_, caput xxi.
The meaning of this may be expressed as follows:--Attached to the twelve months of the year are certain fixed numbers called regulars, ranging from I to VII, denoting the days of the week in their usual order. These regulars, in any year whereof the concurrent, or solar epact, is 0 or 7, express, of themselves, the commencing day of each month: but in other years, whatever the solar epact of the year may be, that epact must be added to the regular of any month to indicate, in a similar manner, the commencing day of that month.