Isaac Newton and the Calender of Numa Pompilius

[ancusmitis]

So, some of us may know that today, under the old Julian calender (which was in use in Britain at the time), Isaac Newton was born on this date in 1642. This is still ten days shy of 373 years, since under the Gregorian calendar (already in use on the European continent and long since accepted by Great Britain) the date was 4 January 1643. The space between the two dates has sometimes jokingly been called "the ten days of Newton." ref: https://en.wikipedia.org/wiki/Isaac_Newton_in_popular_culture#Newtonmas

Because this is the sort of geek that I am, I noticed that this was the same number of days missing from the calendar credited (by legend) to Numa Pompilius, the Roman calendar that C. Julius Caesar reformed. Under the calendar of Numa Pompilius, since ten days were missing from the ordinary year, every two years an intercalary month was added during the end of February, lasting either 22 or 23 days, starting at terminalis, which was the twenty-third day of the month. The remaining five days became part of intercalaris. Since the days of Roman months were not numbered sequentially like ours, this did not mess up the dates of festivals. The end of februarius and the end of intercalaris would both be counting down to the Kalendae of Martius, so festivals all stayed on the same "date." It's under the Julian reform that the practice began of adding only a single say to February every four years, giving a total Julian year length of 365.25 days. The Gregorian reform removes the extra day from a few years that would otherwise have been leap years, giving a year of 365.2425 days; for example, 1700, 1800, and 1900 were not leap years, but the year 2000 was. The solar year is still just a tiny bit shorter than this, but the Gregorian calendar only gets one more day ahead of the solar year every 3226 years. Under the Julian reckoning, a day was gained every 128 years. ref: https://en.wikipedia.org/wiki/Nones_(calendar)#Intercalation ref: https://en.wikipedia.org/wiki/Julian_calendar

Numa's calendar gives us an opportunity (or it does me, anyway). We can place the ten days of Newton between 25 December and 4 January (Latinized as Neutō, neutōnis; the Latin alphabet does not have a w) and January under the new calendar can begin on 5 January of the Gregorian calendar.

The rest of the calendar works as follows, same month lengths as Numa's calendar:

Ianuarius (29 days)
Februarius (28 days)
Martius (31 days)
Aprilis (29 days)
Maius (31 days)
Iunius (29 days)
Quintilis (AKA July) (31 days)
Sextilis (AKA August) (29 days)
September (29 days)
October (31 days)
November (29 days)
December (29 days)

You see we have two types of month, long and short. They alternate between 31 and 29 days, instead of 31 and 30 like the Julian and Gregorian calendars. The Julian reform added one day to all the short months, except January, Sextilis, and December, which got two. That's what takes you from 355 days to 365. Quintilis and Sextilis had their names changed later, after C. Julius Caesar had already died.

As I said above, Romans did not count days sequentially like we do, but they counted down to 3 fixed dates in each month. I don't know when this practice died out, but it wasn't abolished by Caesar; must have happened some time later. The Kalendae was always the first day of the month, and you would start counting down to it on the day after the ides of the previous month. The Ides was the middle of the month, and in long months it was what we'd call the 15th day; in short months it was on the 13th. So the 16th day of Maius would be ante diem XVII Kalendae Iunii, or the 17th day before the Kalendae of June (the Kalendae itself is also counted towards your total, even though it's technically what you are counting towards). The 14th day of Ianuarius would be ante diem XVII Kalendae Februarii. 14th day of Februarius would be XVI Kal Mar., since February has only 28 days. You start counting down to the ides on the day after the nones, which in long months were the 7th day and in short months it was the 5th. You count down to the nones on the day after the Kalendae. When Caesar added days to the months, he put them all at the very end; so the day after the ides of Ianuarius was XIX Kal. Feb, instead of XVII as it had been under Numa's calendar. The other dates in January all stayed the same.

I have added Newton between December and January, starting with Christmas. Newton will always begin on Christmas day, and the countdown will start at eleven (remember, the day you're counting towards is one, the day before it is two, and so on). The actual day Neuto will correspond to 4 January on the Gregorian calendar, since we're synching with Gregorian dates and not Julian ones; the next day will be Kalendae Ianuarii. After that, you begin counting down to the nones; since January is a short month, the nones is on the fifth day, corresponding to the gregorian date of 9 January. So 6 January (Gregorian) will instead be the second day of the month of Ianuarius, which is ante diem IV Nones Ianuarii. 7 January will be III Nones. 8 January will be II nones, or pridie nones. 9 January will simply be the Nones. Then 10 January will be ante diem VIII Idus Ianuarii. 31 January will be IV Kalendae Februarii, while the Kalendae Februarii will correspond to the Gregorian date of 3 February.

Since December is now followed by Newton instead of January, the last (that is, 29th) day of December will be terminalis. This gives you something to count down towards in December besides the Kalendae of Ianuarius, since Newton doesn't have a Kalendae. So the day after the ides of December will be XVI Terminalis. The intercalary day comes the day after Terminalis. That means all dates from XI Neutonis until V Kalendae Martii will always correspond to the same Gregorian dates, but the correspondence will differ by one day between leap years and ordinary years. The Gregorian date for IV Kalendae Martius will be 29 February in leap years, while in ordinary years it will be 1 March.

My gods, I spent all day on this. I am a gigantic ****ing nerd.

 

[Naturalist]

So, some of us may know that today, under the old Julian calender (which was in use in Britain at the time), Isaac Newton was born on this date in 1642. This is still ten days shy of 373 years, since under the Gregorian calendar (already in use on the European continent and long since accepted by Great Britain) the date was 4 January 1643. The space between the two dates has sometimes jokingly been called "the ten days of Newton." ref: https://en.wikipedia.org/wiki/Isaac_Newton_in_popular_culture#Newtonmas

Because this is the sort of geek that I am, I noticed that this was the same number of days missing from the calendar credited (by legend) to Numa Pompilius, the Roman calendar that C. Julius Caesar reformed. Under the calendar of Numa Pompilius, since ten days were missing from the ordinary year, every two years an intercalary month was added during the end of February, lasting either 22 or 23 days, starting at terminalis, which was the twenty-third day of the month. The remaining five days became part of intercalaris. Since the days of Roman months were not numbered sequentially like ours, this did not mess up the dates of festivals. The end of februarius and the end of intercalaris would both be counting down to the Kalendae of Martius, so festivals all stayed on the same "date." It's under the Julian reform that the practice began of adding only a single say to February every four years, giving a total Julian year length of 365.25 days. The Gregorian reform removes the extra day from a few years that would otherwise have been leap years, giving a year of 365.2425 days; for example, 1700, 1800, and 1900 were not leap years, but the year 2000 was. The solar year is still just a tiny bit longer than this, but the Gregorian calendar only gets one more day ahead of the solar year every 3226 years. Under the Julian reckoning, a day was gained every 128 years. ref: https://en.wikipedia.org/wiki/Nones_(calendar)#Intercalation ref: https://en.wikipedia.org/wiki/Julian_calendar

Numa's calendar gives us an opportunity (or it does me, anyway). We can place the ten days of Newton between 25 December and 4 January (Latinized as Neutō, neutōnis; the Latin alphabet does not have a w) and January under the new calendar can begin on 5 January of the Gregorian calendar.

The rest of the calendar works as follows, same month lengths as Numa's calendar:

Ianuarius (29 days)
Februarius (28 days)
Martius (31 days)
Aprilis (29 days)
Maius (31 days)
Iunius (29 days)
Quintilis (AKA July) (31 days)
Sextilis (AKA August) (29 days)
September (29 days)
October (31 days)
November (29 days)
December (29 days)

You see we have two types of month, long and short. They alternate between 31 and 29 days, instead of 31 and 30 like the Julian and Gregorian calendars. The Julian reform added one day to all the short months, except January, Sextilis, and December, which got two. That's what takes you from 355 days to 365. Quintilis and Sextilis had their names changed later, after C. Julius Caesar had already died.

As I said above, Romans did not count days sequentially like we do, but they counted down to 3 fixed dates in each month. I don't know when this practice died out, but it wasn't abolished by Caesar; must have happened some time later. The Kalendae was always the first day of the month, and you would start counting down to it on the day after the ides of the previous month. The Ides was the middle of the month, and in long months it was what we'd call the 15th day; in short months it was on the 13th. So the 16th day of Maius would be ante diem XVII Kalendae Iunii, or the 17th day before the Kalendae of June (the Kalendae itself is also counted towards your total, even though it's technically what you are counting towards). The 14th day of Ianuarius would be ante diem XVII Kalendae Februarii. You start counting down to the ides on the day after the nones, which in long months were the 7th day and in short months it was the 5th. You count down to the nones on the day after the Kalendae. When Caesar added days to the months, he put them all at the very end; so the day after the ides of Ianuarius was XIX Kal. Feb, instead of XVII as it had been under Numa's calendar.

I have added Newton between December and January, starting with Christmas. Newton will always begin on Christmas day, and the countdown will start at eleven (remember, the day you're counting towards is one, the day before it is two, and so on). The actual day Neuto will correspond to 4 January on the Gregorian calendar, since we're synching with Gregorian dates and not Julian ones; the next day will be Kalendae Ianuarii. After that, you begin counting down to the nones; since January is a short month, the nones is on the fifth day, corresponding to the gregorian date of 9 January. So 6 January (Gregorian) will instead be the second day of the month of Ianuarius, which is ante diem IV Nones Ianuarii. 7 January will be III Nones. 8 January will be II nones, or pridie nones. 9 January will simply be the Nones. Then 10 January will be ante diem VIII Idus Ianuarii. 31 January will be IV Kalendae Februarii, while the Kalendae Februarii will correspond to the Gregorian date of 3 February.

Since December is now followed by Newton instead of January, the last (that is, 29th) day of December will be terminalis. This gives you something to count down towards in December besides the Kalendae of Ianuarius, since Newton doesn't have a Kalendae. So the day after the ides of December will be XVII Terminalis. The intercalary day comes the day after Terminalis. That means all dates from XI Neutonis until V Kalendae Martii will always correspond to the same Gregorian dates, but the correspondence will differ by one day between leap years and ordinary years. The Gregorian date for IV Kalendae Martius will be 29 February in leap years, while in ordinary years it will be 1 March.

My gods, I spent all day on this. I am a gigantic ****ing nerd.

One detail which puzzles me, relates to the transition between the Julian and Gregorian calendars. I was told in Latin class that the Julian year began with January as ours does, hence it is named for Janus the god with two faces, looking back to the past and forward to the future at the same time. However, seventeenth and eighteenth century Quakers, who rejected the Roman names for the calendar months and days, called the months "First month", "Second Month," etc. However, "First Month" was NOT January, it was March. Which makes me wonder if the Julian calendar in fact started with March, because I don't think that the Quakers in England would have wanted a different calendar year entirely from the rest of the country...? Although they retained March as the "First Month " for several decades after the transition between the Julian and Gregorian calendar. It makes old Quaker records quite difficult to read sometimes.

If I recall correctly, some villages in Wales retain the use of the Julian calendar, in Pembrokeshire perhaps. Many people were not in favor of the change in the 1750s because they lost ten days of work for which they were still to be taxed.

Feel free to share the results of your geekery any time... I feel sad for those who don't find such stuff fascinating...

 

[ancusmitis]

One detail which puzzles me, relates to the transition between the Julian and Gregorian calendars. I was told in Latin class that the Julian year began with January as ours does, hence it is named for Janus the god with two faces, looking back to the past and forward to the future at the same time. However, seventeenth and eighteenth century Quakers, who rejected the Roman names for the calendar months and days, called the months "First month", "Second Month," etc. However, "First Month" was NOT January, it was March. Which makes me wonder if the Julian calendar in fact started with March, because I don't think that the Quakers in England would have wanted a different calendar year entirely from the rest of the country...? Although they retained March as the "First Month " for several decades after the transition between the Julian and Gregorian calendar. It makes old Quaker records quite difficult to read sometimes.

If I recall correctly, some villages in Wales retain the use of the Julian calendar, in Pembrokeshire perhaps. Many people were not in favor of the change in the 1750s because they lost ten days of work for which they were still to be taxed.

Feel free to share the results of your geekery any time... I feel sad for those who don't find such stuff fascinating...

The original calendar, attributed to Romulus, had only ten months, starting with Martius and ending with December. Pompilius's calendar is the one that introduced Januarius and Februarius. I don't know when the first day of the year was fixed on the first of January, but C. Julius Caesar did fix the beginning of the year somewhere. Previously, one of the priests (I forget which one) would have been responsible for determining when the year needed to be lengthened. So people could, and did, skip intercalary months when they ought to have been added, and insert ones when it was inappropriate, to keep their friends in office and shorten the terms of their enemies. Caesar used this power to add two extra intercalary months for the year he was in that office, along with the one that had already been added according to custom. But he also took away the power to do this, setting the length of the year permanently at 365 days, plus one for leap years.

According to wikipedia, the end of the religious year was actually Terminalis (another reason to move that day to the end of December). I can't think of a reason to specify that it's the religious year except if the civil year was different. But perhaps I'm reading too much into it. In truth, I need more primary sources for the calendar. But until then, this is just what was burning through my mind. Livy mentions that Pompilius reformed the calendar, but he doesn't go into detail. The wikipedia article cites Macrobius and Plutarch. Could be a place to start.