[tz] Leap year bugs

Brian Inglis Brian.Inglis at SystematicSw.ab.ca
Fri Jan 24 05:00:44 UTC 2020


On 2020-01-23 15:23, Clive D.W. Feather wrote:
> Brian Inglis said:
>>>> [OT: Note the date issued on the Julian Calendar: as it was not an O.S. leap
>>>> year this was not the leap day; the year changed on Lady Day March 25 (O.S.);
>>> In England but not in Scotland, which had moved to the 1st January rule well
>>> before.
> 
> I meant well before 1752; I don't know when (or if they ever used the Lady
> Day convention).
> 
>> Probably for continental commercial reasons regardless of religious
>> considerations, while keeping an eye on the crown to free up down south.
> 
> Union of crowns was 1603; union of Parliaments was 1707.

Yes - we started using January 1 as the New Year in 1599/1600, instituted
Hogmanay/Ne'erday as the winter festival in 1604, abolished Yule in 1640,
resuming celebration in 1958; this and many other holy days and feast days were
abandoned as superstitious observations by the Calvinist Presbyterians.

>>> It's my understanding that the insertion of 29th February was done on the
>>> basis of the Scottish system, not the English one, so there was a 29th
>>> February in 1743 and in 1747.
>> Was there a different Julian/O.S. system in Scotland, and are there docs/refs?
> 
> I didn't make that clear, did I?
> 
> My understanding (and, no, I don't have references) is that all of Europe
> had 29th February (whether the leap day is VI Kal.Mar. or 29th February is
> a notational matter and not relevant) in the same Februaries, so that the
> 29th February would be in 1743 and 1747 in England but in 1744 and 1748 in
> Scotland *but it's the same February*.

So the new year celebrated in that 12 month period was used to determine when
leap years occurred.

Until at least the Gregorian reform European clerks used the Latin Roman Julian
Calendar, as in the dates throughout Inter gravissimas linked previously, as few
others were literate or numerate, with minor variations such as the assumption
that all numbers were ante diem - subtracted from the Kalends, None, or Ides,
using Roman counting inclusive of both start and end dates.

The leap day was apparently still considered effectively to be added after ante
diem sexto Kalendis Martis (February 24), giving ante diem bis sextus Kalendis
Martis, second sixth (inclusive count) day before March 1, which is why that is
not mentioned in the bull.

It was probably not until the common use of Hindu-Arabic numerals replacing
Roman numerals in calendars (apparently undocumented so far) when February
having 29 days gave rise to the belief that the added day was the 29th.

>>>> still observed as HM gov fiscal and taxation year end April 5 (N.S.) as they
>>>> were not giving up 11 days of taxes in 1751/2!]
>>> Just 1752; that was the first year that England changed rule. So 1751 was
>>> only 278 days long in England (and had no January or February at all);
>>> February 29th 1752 existed throughout the Union.
>>
>> You mean as January/February/March until 24th were still considered 1750 (O.S.)?
> 
> Yes.
> 
>> Did the Empire change year numbering on January 1 from O.S. to N.S., prior to
>> changing the calendar from Julian to Gregorian on September 14?
> 
> Yes: this was specified in the New Calendar Act.
> 
> England     Scotland

> 1750-12-31  1750-12-31
> 1750-01-01  1751-01-01
> ...         ...
> 1750-02-28  1751-02-28
> 1750-03-01  1751-03-01
> ...         ...
> 1750-03-24  1751-03-24
> 1751-03-25  1751-03-25
> ...         ...
> 1751-12-31  1751-12-31
> 1752-01-01  1752-01-01
> ...         ...
> 1752-02-28  1752-02-28
> 1752-02-29  1752-02-29
> 1752-03-01  1752-03-01
> ...         ...
> 1752-03-24  1752-03-24
> 1752-03-25  1752-03-25
> ...         ...
> 1752-09-02  1752-09-02
> 1752-09-14  1752-09-14
> ...         ...
> 1752-12-31  1752-12-31
> 1753-01-01  1753-01-01
> ...         ...

Interesting, thanks.

-- 
Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

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