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CHRISTMAS Day this year falls on the 4 nivose of the year 198, according
to the French Revolutionary calendar. Two hundred years ago the French Revolution
swept aside the ancien regime, and set about overturning the old ways and
ideas, replacing them with principles based on reason.

The scientists of the revolution attempted two great reforms. The first
involved a new system of weights and measures. In place of a hotch potch
of measures, the livre, pied and pouce (which were not quite the same as
the English pound, foot and inch), came the new metric system, which embodied
the decimal principle. The second resulted in a new calendar. In place of
the Gregorian calendar, with its religious associations and its confusing
names for the months (October, November and December are actually the 10th,
11th and 12th months), the scientists devised a system in which the names
of the months reflected the seasons of the year – thermidor in summer, for
example, brumaire for the autumn fogs, ventose for the spring gales. Although
the year was still divided up into 12 months, time in the new system was
decimal. Ten hours spanned the day, each hour was subdivided into decimales,
or minutes, and each minute into seconds.

So far, so rational. The metric system of measurement, after prolonged
resistance from the Anglo-Saxon world, is now the established scientific
standard, and is slowly infiltrating into ordinary life among English speakers.

The revolutionary calendar, however, lasted for just 17 years. It went
the way of the First Republic. When Napoleon became emperor he dropped the
calendar. And apart from a brief revival during the short life of the Paris
Commune in 1871 it vanished. (Napoleon also tried to drop the metric system,
which was officially abandoned by France in 1812, and not readopted until
1840.) So why did the scientists of the revolution consider it necessary
to introduce a new calendar, and how did we end up with the Gregorian calendar,
which it replaced, but which we still use today? Ancient people started
measuring time by looking at the heavens. The Sun’s passage overhead defines
the day. The same body lays down the year. The Moon’s circuit of the Earth
became the month, as that word’s etymology suggests.

For early people these measures of time had different uses. Farmers
were interested in the seasons and hence the year, if only because crops
planted in autumn did not fare as well as those planted in spring. However,
nomads in the desert countries had little interest in the time for planting
crops, as they did not rely on them for food. They tended to look to the
Moon instead. The Islamic calendar is one of the few in the modern world
still to be based on the Moon.

The problem for all calendar makers throughout history is that there
is no simple way of relating the movement of the Moon to that of the Sun,
nor of relating the day to the solar year. The calendar of the Roman republic
attempted to reconcile the pulls of the Sun and the Moon. Its year was 366.25
days long. By 46 BC the Roman calendar was in such a mess (the spring equinox
was in the middle of May) that Julius Caesar had to decree a year of 445
days before introducing a reformed calendar.

The calculation of the length of the year and the drawing up of Caesar’s
new calendar was the work of Sosigenes, an astronomer of Alexandria, the
Greek city of learning in Egypt. The Julian calendar, as it became known,
was based on a year of 365.25 days. It had three years of 365 days, and
a leap year, with an extra day. The problem with this calendar was that
the year is not precisely 365.25 days long, although it is near enough for
all normal purposes. The tropical year (the year as measured at the Equator)
is slightly more than 11 minutes shorter than the Julian year.

Over the centuries the calendar and the solar year slowly came adrift
as the error accumulated. By the time the Gregorian calendar was introduced
in 1582 the vernal equinox, 25 March when the Julian calendar was established,
had become 11 March. The main reason for the switch to the Gregorian calendar
was religious. The religious festivals at that time were still based on
the Moon, just as they had been in ancient Rome. The council of Nicea, in
AD 325, had laid down that Easter had to be celebrated on the first Sunday
after the full Moon following the equinox.

Acting on the advice of a commission led by the Jesuit astronomer Christopher
Clavius, Pope Gregory XIII laid down the new calendar, and by papal bull
decreed that 5 October become 15 October. To maintain this correction, the
century years would become leap years when they were divisible by 400. Thus
1600 was a leap year, 1700, 1800 and 1900 were not, and since we are still
using the Gregorian calendar, 2000 will be a leap year.

The Gregorian calendar swiftly became bogged down in the politics of
the time. The principal catholic countries, France, Spain, Portugal and
parts of Italy, quickly adopted it. In France this meant that Monday 20
December 1582 followed Sunday 9 December; and the people had to accept this.
However, the protestant countries held out against the papal theft of days.
In England, John Dee, Queen Elizabeth I’s astrologer and court alchemist,
did produce a rival correction, of 11 days, but the bishops vetoed it. Scotland
adopted the Gregorian calendar in 1600, and most of Germany had converted
by the end of the 17th century.

England did not fall into line until 1752. In London the mob ran riot,
believing that the government had short-changed them. ‘Give us back our
eleven days,’ they shouted. Meanwhile, the orthodox church clung to the
old ways. Russia did not change until after the October Revolution of 1917,
which according to the Gregorian calendar took place in November. Greece
was the last European country to change, in 1923.

The Gregorian calendar is far from perfect. It has 97 leap years in
every 400 years, which is roughly one too many. In 1900, the solar year
was 365.24219879 days long and getting shorter by 0.00006 days every 1000
years. In the Gregorian calendar, the year is 365.2425 days long.

In 1789, the religious links of the Gregorian calendar made a natural
target for the new revolutionary government in France. Reform of the calendar
became inextricably linked with reform of the system of measurement. On
9 March 1790 the Bishop of Autun, Charles Maurice de Talleyrand, proposed
a new unified system of measurement. In October of that year a commission
set up by the French Academy of Sciences proposed that the new systems should
adopt the decimal principle. The chemist Antoine Lavoisier and the mathematician
Joseph-Louis Lagrange were both members of this commission. Lagrange was
active in formulating both the metric system and the new calendar.

Some of the best minds of revolutionary France gathered together to
carry out the great reforms. Gilbert Romme, who was 40 at the time, and
had been associated with the encyclopedists, was the moving spirit behind
the new calendar. In Romme’s team were not only Lagrange, but Joseph-Jerome
Lalande, the astronomer whose planetary tables were the best available,
the playwright Fabre d’Eglantine, and Jean Delambre, an eminent astronomer
who carried out the surveys necessary to measure the meridian and thus establish
the length of the new metre.

Romme presented his report to the revolutionary parliament, La Convention
nationale, on 20 September 1793. His team had done its work well. Romme’s
report says thatthe year is 365 days 5 hours 48 minutes 49 seconds long,
just three seconds longer than we think it is today, an accuracy of about
one in 10 million.

In the French Revolutionary calendar there were 12 months, which, initially,
were given numbers instead of names. Each month lasted 30 days. The beginning
of the year was the autumn equinox. At the end of the year there werefive
(or in leap years six) days of holiday known asthe sansculottides, which
were set aside for ordinary people(the sans culottes, who could not afford
the aristocrat’s culottes) to celebrate.

The days of the month were divided into three groups of ten, or ‘decades’,
with each day of the decade having a number for a name (primidi, duodi and
so on). There was also a system of names for days, taken from animals, flowers
and plants, one for each day of the year.

In his report Romme advocated that the new calendar should be backdated
to 22 September 1792, the day on which the republic was founded following
the abolition of the monarchy (or the day the vulgar era ended, as his report
puts it). By happy coincidence, 22 September was also the autumn equinox
that year. On 22 September 1793, the Convention approved Romme’s report.

On the 14th day of the First month (5 October according to the Gregorian
calendar) the Convention decided to adopt the revolutionary calendar, together
with numerical names for the months and days. By the 27th day of the First
month the Convention had clearly got fed up with the system of numbering
months, and it ordered Romme and the poet Fabre d’Eglantine to find names
for them instead.

Six days later d’Eglantine came back with the required list: for the
autumn months, vendemiaire, brumaire and frimaire; for winter, nivose, pluviose
and ventose; for spring, germinal, floreal and prairial; and for summer,
messidor, thermidor and fructidor. The Convention adopted the names, on
3 brumaire. Two days earlier the Convention had ordered specimen metric
weights and measures to be manufactured. And on 19 brumaire the Convention
distributed a unified decree on the adoption of the new calendar.

However satisfying Romme’s calendar was from a scientific point of view,
the average citizen in the street found it hard to understand. For this,
one must largely blame the authorities, who, in introducing a new calendar,
seemed a little confused themselves. The problem concerned the starting
date. Article 373 of the French Constitution of 1795 states categorically
that the new era began on 22 September 1792, the day on which the republic
was founded. However, before arriving at that date, the authorities had
made several false starts.

Initially, and before the scientists had produced their calendar, pamphlets
had appeared on the streets describing 1789, the year of the fall of the
Bastille, as year I of the new era. But did this mean that year I began
on 1 January 1789, or on 14 July – Bastille Day? It took three years for
the French legislative assembly to decide this point. Year IV of the new
era, it declared on 2 January 1792, began on 1 January 1792. However, by2
January 1793, the assembly had changed its mind. Year IIof the new era began
yesterday, it decreed, on 1 January 1793. By the time the starting date
was finally confirmed as 22 September 1792, the average citizen driving
the tumbril, wanting to start the new year with a hangover, must have been
thoroughly confused.

The job of promoting the new calendar fell upon the Comite d’Instruction
publique. This organisation had been set up by the French legislative assembly
in 1791 with the task of disseminating information about culture, science
and technology; in many respects, the UNESCO of its day. As well as distributing
the decrees and producing a users’ manual, the committee also put on a ballet,
called Calendrier republicain, first performed at Bordeaux on 4 frimaire
of year II. It also helped to promote the new weights and measures, and
a system of decimal coinage, introduced in 1793.

By making the start of the year depend on a natural phenomenon, such
as the equinox, the revolutionary reformers avoided the problem of the Julian
calendar, where a seemingly trivial error becomes magnified over the years.
However, it created practical difficulties.

Romme and his team had envisaged that every fourth year would be a sextile
(the equivalent of the Gregorian leap year) and have 366 days. The first
sextile did indeed fall every four years: years III, VII, XI and XV. However,
because the start of the year was dependent on the equinox, and the equinox
is no respecter of calendars, the next sextile would have to have been year
XX. Lalande was the first to notice this problem.

Also, the practical value of never being too far out of step with nature
was obviated by there being no easy correspondence between the Gregorian
and the revolutionary calendars. Thus, for example, although Christmas Day
1989 would have fallen on 4 nivose according to the French Revolutionary
calendar, Christmas Day last year would have fallen on 5 nivose.

Perhaps the most logical part of the new system was the decimal division
of the day. It was also the first to go. The division of time in sixtieths
is a Babylonian inheritance, and has no natural basis. On 10 ventose of
year III (1795) the Convention received a report on further measures needed
to ensure the introduction of the metric system. On the same day it abandoned
the decimal division of time.

By 29 germinal of year III, Delambre, then in the middle of measuring
the meridian, proposed reforming the sextiles. Lalande, Lagrange and others
discussed the idea. Three weeks later, on 19 floreal, Romme submitted a
proposal for reform of the sextiles to the Convention. The sextiles would
fall every four years, with the exception of the 400th year and the 4000th
year. This gave a mean year of 365.24225 days, an error of five days in
100 000 years.

By this time, there was a certain tension between the revolution and
its scientists. Lavoisier had been executed the year before, one reason
given being that ‘the revolution has no need of scientists’. The scientists
had also had their differences among themselves. Delambre, who seems to
have been an irascible character, had disputes with both Lavoisier and Romme.

One possibly apocryphal tale has Romme coming before the Convention
with his report for the reform of the sextiles and asking for a new decree
because he had discovered a problem with the calendar that would occur in
3600 years’ time. Romme asked for his solution to be adopted ‘for the honour
of astronomy’. One committee member asked ‘Do you expect us to legislate
for eternity?’, and demanded a 3600-year adjournment. He got it.

The following month, on the night of 1 prairial, Romme and several other
prominent revolutionaries were arrested. Romme was condemned to death on
29 prairial which, according to one account, was the day on which his report
was circulated to the Convention. In the event, he committed suicide. In
so doing, he at least escaped the fate of another of those arrested on 1
prairial, who was executed and had his head paraded around the Convention
shortly before it sentenced him to death. Another account has the Convention
discussing Romme’s report on the day he committed suicide.

Five days after Romme’s death the Convention set up a body known as
the Bureau of Longitudes. A month later, the bureau, perhaps prudently,
told the Convention that it no longer wanted to reform the sextiles.

The problem with the sextiles was not the only difficulty facing the
calendar. On 24 thermidor of year III (11 August 1795) one group of revolutionaries
petitioned the Convention to abandon it. At the outset, said the petition,
there is the ridiculous dispute each year about whether the year starts
on 22 or 23 September. The new names for the month are true in the north,
but not the south. Why is it, they pleaded, that one of the most solemn
religious festivals is known as the day of the dog? (An alternative name
for 5 nivose, Christmas Day in years II and III, was le jour du chien.)
But perhaps the real complaint – it certainly comes across with the most
fervour – was that in most countries workers had one day off a week. In
France, the revolutionary calendar meant that there was only one day off
in every ten. ‘Neither men nor animals can bear nine consecutive days of
work,’ the petitioners claimed.

In fact, the petition failed. The authorities pressed on with their
reforms and the calendar was embodied in the constitution on 3 vendemiaire
of year IV (1795). In year VI the authorities issued scales for converting
old weights and measures to metric units, and a new law made observance
of the calendar compulsory. In year VII (11 floreal) Delambre finished measuring
the arc from Dunkirk to Barcelona, and deduced the length of the metre.
The accuracy of his measurement was about 3 in 100 000.

The explanation usually given for the failure of the calendar is that
it caused problems for commerce. Certainly, there were difficulties. Under
the revolutionary calendar, you needed to know the dates of two autumn equinoxes
before you could order, say, a cargo of claret. On the other hand, easternand
western Europe traded quite happily on two different calendars for the best
part of 250 years before the FirstWorld War.

More to the point was the change from republic to empire, with the church
resuming much of its old power. On 18 brumaire of year VIII (9 November
1799), Napoleon launched his coup d’etat. Observation of the decades became
obligatory for state employees only. The churches reopened. On Sunday the
people went to their masses. The return to the seven-day week robbed the
calendar of one of its main advantages – the simplicity of the 30-day month.
The next year the state halted the decimalisation of weights and measures.
In year X even state employees were given Sundays off.

In year XIII the move to abandon the calendar became more serious. By
now, the chief argument for returning to the old calendar was the failure
of Romme’s attempt to reform the sextiles.

On 28 floreal XII Napoleon became emperor. His coronation, in Notre
Dame, took place on 13 frimaire of year XIII. A year later Napoleon’s government,
observing that in practice two systems of dates were being used in France,
finally put paid to the revolutionary calendar. It ordered: ‘A compter du
11 nivose prochain, 1 janvier 1806, le calendrier gregorien sera mis en
usage dans tout l’Empire francais.’ Six years later, the government also
ordered a return to the old measures. France did not finally go metric until
1840.