Dr J R Stockton wrote;
Judging from quotations elsewhere, that will be Butcher's algorithm.

It is indeed. Meeus merely states that it was devised in 1876 and
appeared in Butcher's Ecclesiastical Calendar, then Spencer Jones'
General Astronomy 1922, then in the journal of the BAA, Vol. 88 (Dec.
1977).

Otto Mortensen's book, "Jens Olsen's Clock, a technical description",
gives a detailed description of the method of calculation used for the
calendar work, albeit with small printing errors, but it fails to
indicate the origin of the 15 year period called the "cycle of
indiction" used in the calculation, other than to say that it has no
connection with astronomical periods.
It states that nothing is known for certain about it's origin, but _may_
have been used by the Romans, possibly as an interest, or fiscal term,
but it continues from that time throughout the reckoning.

I have toyed with the idea of typing up the calendar work pages, just
because (a) I found it fascinating and thought others might too, and (b)
the book seems rather rare and not easily accessible to amateur
astronomers.
I have no idea if this would be a copyright infringement, but it may be
allowed under the clause covering "short passages for the purpose of
review".
Is anyone interested?
--
Denis
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