In A
Calendar for Your Date — Part I, I mentioned the changeover from the Julian
calendar to the Gregorian calendar. People who have read about this may have
heard terms such as dual dates, double dates, double years, new/old style,
but do you really know what they mean? Was the handling of this changeover a
special case — one that needs its own treatment in our data — or was it really
an example of a generalised case? It’s time to take the lid off.
Figure 1 - Synchronised swimming in a sea of dates.
The Gregorian calendar was introduced by papal bull on Thursday
4 Oct 1582, Julian (followed by Friday 15 Oct 1582, Gregorian), but a couple of
factors prevented its automatic adoption everywhere. One of these was the fact
that it was devised by the Roman Catholic Church, and so in a time of
especially fraught church tensions other churches saw it as some type of power-play
and resisted. For instance, although other Catholic countries in Europe adopted
it either immediately (e.g. Spain), or later that year (e.g. France), or the
following year (e.g. Netherlands), Britain, including its colonies — some to
later become part of the US — didn’t change until Wednesday 2 Sep 1752, Julian
(followed by Thursday 14 Sep 1752, Gregorian; the difference by that time being
11 days rather than 10). Another factor was that many people considered that
days were being stolen from them — between 10 and 13 days, depending on the
date that their changeover occurred. Birthdays and anniversaries changed,
events changed, and that shortened year (282 days for Britain) created
difficulties for handling taxes, deadlines, and interest.[1] So
why were days taken away?
To understand this, it is important to know the reasons for
the calendar change. The length of the Julian year was too long (365.25 days)
and that meant that the Easter date was drifting backwards from the traditional
date as defined by the early church. There were therefore two main parts to the
calendar change: the solar part whereby new leap-year rules corrected the
average year to 365.2425 (much closer to the measured average of 365.24219
days), and the lunar part which corrected the cumulative error of 13 centuries
of drift by removing 10 days.
To complicate things slightly more, the British year was
also deemed to start on the 1st January rather than the 25th
March (Lady
Day) that it had done since the 12th Century (except in Scotland
where they had already changed in 1600). The UK Calendar (New Style) Act 1750,
which introduced the calendar changeover, justified the adjustment of the civil
year by “Whereas the legal supputation of the year of our Lord in England,
according to which the year beginneth on the twenty-fifth day of March, hath
been found by experience to be attended with divers inconveniences, not only as
it differs from the usage of neighbouring nations, but also from the legal
method of computation in Scotland, and from the common usage throughout the
whole kingdom, …”.[2] Note
that 1st January had long been celebrated as the start of the
“historical year” (New Year’s Day) but the Gregorian calendar was essentially a
civil calendar, and this was part of the reason why the church could not
mandate it. The terms Old Style (O.S.)
and New Style (N.S.) are often used
to clarify the ambiguities of dates falling between 1st January and
24th March. Old Style meant
that something was dated according to the old civil year and so must be
adjusted to align with the New Style
civil year, or to the historical year.[3]
The fact that the civil and historical years were already
different in Britain, even before the calendar changeover (except in Scotland),
meant that there was already a means of representing a year combination using a
notation informally called double years.
For instance, 3rd March 1733/4 clarified that this was March of the
civil year 1733 and of the historical year 1734 (i.e. the month before April
1734). Following the Julian-to-Gregorian
calendar change, the difference of 11 days meant that it was not just the year
that was different; a date such as 10/22 January 1705/6 explicitly represented
both the Julian and Gregorian dates, including their corresponding years.[4]
This was another form of a dual
date, or double date although
this term is no longer preferred due to the ambiguity with the social occasion of the same
name.
Even today, the start of the old civil year affects everyday
life in Britain since the start of the personal tax year remained at 25th
March (O.S.), or 5th April (N.S.), until 1800 when it moved to 6th
April. Britain also retains a double-year
notation to indicate that a tax year spans two year numbers, e.g. 2011/12.
Although Easter should fall on the Sunday following the full
moon that follows the northern spring equinox, both the full moon and the
equinox are now determined by calendar rules rather than direct observation.
This means that the date calculation (Computus) now differs in
different calendars, in different localities, and in different religions. Not
all holy festival dates were moved during the changeover, though; the date of
Christmas was already 25th December in the Julian calendar. This was
subsequently retained by all Western churches, and by some Eastern ones. The
equivalent Julian date (in this present time) would be 7th January,
and some churches do continue to use that date.
A large part of the confusion must be attributed to the fact
that the same calendar era was used — meaning that year numbering was designed
to run, as consecutively as possible, from the previous ones — and that the
same month names and day counts were retained. Hence, when birthdays or
anniversaries had been “bumped up”, it appeared to be a seriously intrusive
change, despite the measurement actually being according to a different
calendar scale. It is interesting to observe that this demonstrates how
indispensable the notion of a calendar had become, and how people attached
greater significance to the day number and month name than to the actual time
of the year.
If the change had merely included new leap-year rules then
no one would have noticed until the next difference (year 1700). Even the
change of the year start would have been manageable since countries such as
Scotland had already achieved it. However, the correction of 10 days, combined
with retention of the old months, appeared as though days were being stolen,
and it supposedly caused riots. Finally, the pope’s bull came at a very
difficult time as far as relations between the Catholic and Protestant churches
were concerned. It was issued in the reign of Elizabeth I and in 1584 a
previous attempt was made to adopt it. An act was prepared entitled ‘An act to
give Her Majesty authority to alter and make a new calendar, according to the
calendar used in other countries’. Although the bill passed two readings in the
House of Lords, stalling tactics by Protestant bishops ensured that it was
eventually ignored.[5]
When we observe dual
dates written during this chaotic transition, or from the period before,
when the civil and historical years differed, we can identify two dates
expressed according to distinct calendars: the Julian and Gregorian, or Julian
with civil and historical years, respectively. In other words, it was not
always the case that dual dates
represented Julian and Gregorian dates during the changeover — a common
misconception. What the cases have in common is that the date pairs represented
the same day.
In A
Calendar for Your Date — Part II, I made a case for holding an additional
normalised (computer-readable) version of our dates, but how should this be
extended to such pairs? The situation is not a special case as there are other
precedents for representing the same day according to different calendars. In
Israel, for instance, government documents usually carry a dual date embracing both the traditional Hebrew calendar and the
Gregorian calendar. Similarly, following the calendar reforms of India, in
1957, government documents carry a dual
date embracing the new national calendar of India and the Gregorian
calendar.
STEMMA therefore defines the notion of synchronised dates, where a single entity describes an item from a
written or printed source that embraces representations of the same day
according to two or more calendars. To see this in action, let’s look at the
combined Julian-Gregorian date example from above:
Figure 2 - Synchronised Julian and Gregorian
dates.
We can immediately see that the one evidential form — that
obtained from the consulted source — yields two normalised forms: one according
to the Julian calendar and one to the Gregorian calendar. Any number of display
forms can be generated from these normalised forms, dependent upon the regional
settings and personal preferences of the end-user.
Anyone who hasn’t read my previous two articles on dates
might be wondering why we need to store two normalised values when one will do,
employing a conversion algorithm when necessary. However, note that not all
such dual dates have an obvious
interpretation. For instance, double
years were occasionally used for months other than January to March which
makes little sense, and so needs some considerable interpretation. These two
normalised forms provide a direct interpretation of the relevant parts of the
evidential form.
When other calendars are considered then the conversion to the
Gregorian calendar — necessary for date comparison and timelines — is not
always reliable. In these circumstances, the same entity can describe the
direct interpretation of the evidential form and the calculated version
of it. I’ll return to the French Republican calendar example from the
aforementioned article in order to demonstrate such a conversion:
Figure 3 - Synchronised French Republican and
calculated Gregorian dates.
In effect, the same synchronised-date entity is used to
represent both dual dates and cases
where a value in an alternative calendar has been calculated. In both
circumstances it binds the multiple derived forms (normalised and/or
calculated) to a single evidential form.
[1] David
Ewing Duncan, The Calendar (London:
Fourth Estate Ltd, 1998), pp.288–289.
[2] “Calendar
(New Style) Act 1750”, transcription, legislation.gov.uk
(http://www.legislation.gov.uk/apgb/Geo2/24/23
: accessed 4 Aug 2015), in introduction; delivered by The National Archives of
UK.
[3] University
of Nottingham , “Historical Year and the Civil Year”, UK Campus: Manuscripts and Special Collections (https://www.nottingham.ac.uk/manuscriptsandspecialcollections/researchguidance/datingdocuments/historicalandcivil.aspx
: accessed 3 Aug 2015).
[4] Mike
Spathaky, "Old Style and New Style Dates and the change to the Gregorian
Calendar: A summary for genealogists", GENUKI
(http://www.cree.name/genuki/dates.htm
: accessed 4 Aug 2015), under "The cause of ambiguities - 2. The Start of
the year".
[5] E. G.
Richards, Mapping Time: The Calendar and
its History (1998; reprint, Oxford University Press, 2005), p.252.
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