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Notes On Time Measurement
Celestial bodies —
the Sun, Moon, planets, and stars — have provided us a reference for
measuring the passage of time throughout our existence. Ancient
civilizations relied upon the apparent motion of these bodies through the
sky to determine seasons, months, and years.
We know little about the details of timekeeping in
prehistoric eras, but wherever we turn up records and artifacts, we usually
discover that in every culture, some people were preoccupied with measuring
and recording the passage of time. Ice-age hunters in Europe over 20,000
years ago scratched lines and gouged holes in sticks and bones, possibly
counting the days between phases of the moon. Five thousand years ago,
Sumerians in the Tigris-Euphrates valley in today's Iraq had a calendar that
divided the year into 30 day months, divided the day into 12 periods (each
corresponding to 2 of our hours), and divided these periods into 30 parts
(each like 4 of our minutes). We have no written records of Stonehenge,
built over 4000 years ago in England, but its alignments show its purposes
apparently included the determination of seasonal or celestial events, such
as lunar eclipses, solstices and so on.
The earliest Egyptian calendar was based on the moon's
cycles, but later the Egyptians realized that the "Dog Star" in Canis Major,
which we call Sirius, rose next to the sun every 365 days, about when the
annual inundation of the Nile began. Based on this knowledge, they devised a
365 day calendar that seems to have begun in 4236 BCE (Before the Common
Era), which thus seems to be one of the earliest years recorded in history.
Before 2000 BCE, the Babylonians (in today's Iraq) used a
year of 12 alternating 29 day and 30 day lunar months, giving a 354 day
year. In contrast, the Mayans of Central America relied not only on the Sun
and Moon, but also the planet Venus, to establish 260 day and 365 day
calendars. This culture and its related predecessors spread across Central
America between 2600 BCE and 1500 CE, reaching their apex between 250 and
900 CE. They left celestial-cycle records indicating their belief that the
creation of the world occurred in 3114 BCE. Their calendars later became
portions of the great Aztec calendar stones. Our present civilization has
adopted a 365 day solar calendar with a leap year occurring every fourth
year (except century years not evenly divisible by 400).
Not until somewhat recently (that is,
in terms of human history) did people find a need for knowing the time of
day. As best we know, 5000 to 6000 years ago great civilizations in the
Middle East and North Africa began to make clocks to augment their
calendars. With their attendant bureaucracies, formal religions, and other
burgeoning societal activities, these cultures apparently found a need to
organize their time more efficiently
Sumerian culture was lost without passing on its knowledge, but the
Egyptians were apparently the next to formally divide their day into parts
something like our hours. Obelisks (slender, tapering, four-sided monuments)
were built as early as 3500 BCE. Their moving shadows formed a kind of
sundial, enabling people to partition the day into morning and afternoon.
Obelisks also showed the year's longest and shortest days when the shadow at
noon was the shortest or longest of the year. Later, additional markers
around the base of the monument would indicate further subdivisions of time.
Another Egyptian shadow clock or sundial, possibly the first portable
timepiece, came into use around 1500 BCE. This device divided a sunlit day
into 10 parts plus two "twilight hours" in the morning and evening. When the
long stem with 5 variably spaced marks was oriented east and west in the
morning, an elevated crossbar on the east end cast a moving shadow over the
marks. At noon, the device was turned in the opposite direction to measure
the afternoon "hours."
The merkhet, the oldest known astronomical tool, was an Egyptian
development of around 600 BCE. A pair of merkhets was used to establish a
north-south line (or meridian) by aligning them with the Pole Star. They
could then be used to mark off nighttime hours by determining when certain
other stars crossed the meridian.
In the quest for better year-round accuracy, sundials evolved from flat
horizontal or vertical plates to more elaborate forms. One version was the
hemispherical dial, a bowl-shaped depression cut into a block of stone,
carrying a central vertical gnomon (pointer) and scribed with sets of hour
lines for different seasons. The hemicycle, said to have been invented about
300 BCE, removed the useless half of the hemisphere to give an appearance of
a half-bowl cut into the edge of a squared block. By 30 BCE, Vitruvius could
describe 13 different sundial styles in use in Greece, Asia Minor, and
Elements of a Clock
Before we continue describing the
evolution of ways to mark the passage of time, perhaps we should broadly
define what constitutes a clock. All clocks must have two basic components:
a regular, constant or repetitive process or
action to mark off equal increments of time. Early examples of
such processes included the movement of the sun across the sky, candles
marked in increments, oil lamps with marked reservoirs, sand glasses
(hourglasses), and in the Orient, knotted cords and small stone or metal
mazes filled with incense that would burn at a certain pace. Modern clocks
use a balance wheel, pendulum, vibrating crystal, or electromagnetic waves
associated with the internal workings of atoms as their regulators.
a means of keeping track of the increments of
time and displaying the result. Our ways of keeping track of the
passage of time include the position of clock hands and digital time
The history of timekeeping is the story of the search for ever more
consistent actions or processes to regulate the rate of a clock.
Water clocks were among the earliest
timekeepers that didn't depend on the observation of celestial bodies. One
of the oldest was found in the tomb of the Egyptian pharaoh Amenhotep I,
buried around 1500 BCE. Later named clepsydras ("water thieves") by
the Greeks, who began using them about 325 BCE, these were stone vessels
with sloping sides that allowed water to drip at a nearly constant rate from
a small hole near the bottom. Other clepsydras were cylindrical or
bowl-shaped containers designed to slowly fill with water coming in at a
constant rate. Markings on the inside surfaces measured the passage of
"hours" as the water level reached them. These clocks were used to determine
hours at night, but may have been used in daylight as well. Another version
consisted of a metal bowl with a hole in the bottom; when placed in a
container of water the bowl would fill and sink in a certain time. These
were still in use in North Africa in the 20th century.
More elaborate and impressive mechanized water clocks
were developed between 100 BCE and 500 CE by Greek and Roman horologists and
astronomers. The added complexity was aimed at making the flow more constant
by regulating the pressure, and at providing fancier displays of the passage
of time. Some water clocks rang bells and gongs; others opened doors and
windows to show little figures of people, or moved pointers, dials, and
astrological models of the universe.
A Macedonian astronomer, Andronikos, supervised the
construction of his Horologion, known today as the Tower of the
Winds, in the Athens marketplace in the first half of the first century BCE.
This octagonal structure showed scholars and shoppers both sundials and
mechanical hour indicators. It featured a 24 hour mechanized clepsydra and
indicators for the eight winds from which the tower got its name, and it
displayed the seasons of the year and astrological dates and periods. The
Romans also developed mechanized clepsydras, though their complexity
accomplished little improvement over simpler methods for determining the
passage of time.
In the Far East, mechanized astronomical/astrological
clock making developed from 200 to 1300 CE. Third-century Chinese clepsydras
drove various mechanisms that illustrated astronomical phenomena. One of the
most elaborate clock towers was built by Su Sung and his associates in 1088
CE. Su Sung's mechanism incorporated a water-driven escapement invented
about 725 CE. The Su Sung clock tower, over 30 feet tall, possessed a bronze
power-driven armillary sphere for observations, an automatically rotating
celestial globe, and five front panels with doors that permitted the viewing
of changing manikins which rang bells or gongs, and held tablets indicating
the hour or other special times of the day.
Since the rate of flow of water is very difficult to
control accurately, a clock based on that flow could never achieve excellent
accuracy. People were naturally led to other approaches.
Europe during most of the Middle Ages (roughly 500 CE to 1500 CE),
technological advancement virtually ceased. Sundial styles evolved, but
didn't move far from ancient Egyptian principles.
During these times, simple sundials placed above doorways
were used to identify midday and four "tides" (important times or periods)
of the sunlit day. By the 10th century, several types of pocket sundials
were used. One English model even compensated for seasonal changes of the
Then, in the first half of the 14th century, large
mechanical clocks began to appear in the towers of several large Italian
cities. We have no evidence or record of the working models preceding these
public clocks, which were weight-driven and regulated by a verge-and-foliot
escapement. Variations of the verge-and-foliot mechanism reigned for more
than 300 years, but all had the same basic problem: the period of
oscillation of the escapement depended heavily on the amount of driving
force and the amount of friction in the drive. Like water flow, the rate was
difficult to regulate.
Another advance was the invention of spring-powered
clocks between 1500 and 1510 by Peter Henlein of Nuremberg. Replacing the
heavy drive weights permitted smaller (and portable) clocks and watches.
Although they ran slower as the mainspring unwound, they were popular among
wealthy individuals due to their small size and the fact that they could be
put on a shelf or table instead of hanging on the wall or being housed in
tall cases. These advances in design were precursors to truly accurate
Accurate Mechanical Clocks
1656, Christiaan Huygens, a Dutch scientist, made the first pendulum clock,
regulated by a mechanism with a "natural" period of oscillation. (Galileo
Galilei is credited with inventing the pendulum-clock concept, and he
studied the motion of the pendulum as early as 1582. He even sketched out a
design for a pendulum clock, but he never actually constructed one before
his death in 1642.) Huygens' early pendulum clock had an error of less than
1 minute a day, the first time such accuracy had been achieved. His later
refinements reduced his clock's error to less than 10 seconds a day.
Around 1675, Huygens developed the balance wheel and spring assembly, still
found in some of today's wristwatches. This improvement allowed portable
17th century watches to keep time to 10 minutes a day. And in London in
1671, William Clement began building clocks with the new "anchor" or
"recoil" escapement, a substantial improvement over the verge because it
interferes less with the motion of the pendulum.
In 1721, George Graham improved the pendulum clock's accuracy to 1 second
per day by compensating for changes in the pendulum's length due to
temperature variations. John Harrison, a carpenter and self-taught
clock-maker, refined Graham's temperature compensation techniques and
developed new methods for reducing friction. By 1761, he had built a marine
chronometer with a spring and balance wheel escapement that won the British
government's 1714 prize (worth more than $10,000,000 in today's currency)
for a means of determining longitude to within one-half degree after a
voyage to the West Indies. It kept time on board a rolling ship to about
one-fifth of a second a day, nearly as well as a pendulum clock could do on
land, and 10 times better than required to win the prize.
Over the next century, refinements led in 1889 to Siegmund Riefler's clock
with a nearly free pendulum, which attained an accuracy of a hundredth of a
second a day and became the standard in many astronomical observatories. A
true free-pendulum principle was introduced by R.J. Rudd about 1898,
stimulating development of several free-pendulum clocks. One of the most
famous, the W.H. Shortt clock, was demonstrated in 1921. The Shortt clock
almost immediately replaced Riefler's clock as a supreme timekeeper in many
observatories. This clock contained two pendulums, one a slave and the other
a master. The slave pendulum gave the master pendulum the gentle pushes
needed to maintain its motion, and also drove the clock's hands. This
allowed the master pendulum to remain free from mechanical tasks that would
disturb its regularity.
performance of the Shortt clock was overtaken as quartz crystal oscillators
and clocks, developed in the 1920s and onward, eventually improved
timekeeping performance far beyond that achieved using pendulum and
Quartz clock operation is based on the piezoelectric property of quartz
crystals. If you apply an electric field to the crystal, it changes its
shape, and if you squeeze it or bend it, it generates an electric field.
When put in a suitable electronic circuit, this interaction between
mechanical stress and electric field causes the crystal to vibrate and
generate an electric signal of relatively constant frequency that can be
used to operate an electronic clock display.
Quartz crystal clocks were better because they had no gears or escapements
to disturb their regular frequency. Even so, they still relied on a
mechanical vibration whose frequency depended critically on the crystal's
size, shape and temperature. Thus, no two crystals can be exactly alike,
with just the same frequency. Such quartz clocks and watches continue to
dominate the market in numbers because their performance is excellent for
their price. But the timekeeping performance of quartz clocks has been
substantially surpassed by atomic clocks.
are naturally limited in their usefulness and a cynic might complain that
they are of little more than academic interest in a climate such as that
'enjoyed' in the British Isles. Nevertheless the study of sundials, or
gnomonics as it is sometimes called, will also provide a good understanding
of some fundamental astronomical principles.
Earth rotates on its axis, so the Sun appears to move uniformly across the
sky and if a rod is placed parallel to the Earth's axis its shadow will
naturally move uniformly around itself. In other words, as the Sun moves
through an arc of 15° in the sky in one hour so will the shadow move at the
same rate. This is the principle on which most (but not all) sundials are
based, and in fact the same idea is used with telescopes which are then said
to be 'equatorially mounted'.
Earth's distance from the Sun varies throughout the year and also because
its equator is inclined to its orbit (by 23.5°), there is a difference
between apparent solar time (time told by the Sun) and mean solar time which
is the time kept by mechanical and electrical clocks. In fact it is possible
for the Sun to be as much as a quarter of an hour fast or slow when compared
with a clock which keeps mean solar time (i.e. Greenwich Mean Time). This
difference is called the equation of time and is described in the leaflet
'The Equation of Time'.
If we know
this correction as a function of the date it is possible to adjust certain
types of sundial (those where equal intervals of time are indicated by equal
angles) to allow for the change in the equation of time; or alternatively,
for any type of dial, to apply a correction to the time read from the dial.
correction that has to be made is to allow for the longitude of the place.
We are all familiar with the fact that 'New York is five hours behind
Greenwich' meaning, for example, that when it is midday at Greenwich it is
only 7am in New York. This is because New York is 5 hours of longitude west
of Greenwich. Even if we move only as far west as Bristol we find that this
town is 10 minutes of time west of Greenwich so that the Sun crosses the
meridian 10 minutes later than it does at Greenwich. Therefore if you had a
sundial in Bristol and wanted to find the Greenwich Mean Time, you would
have to add 10 minutes to the time from the dial, unless this longitude
correction had already been allowed for in the construction of the dial.
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Chronology (Greek chronos time, logos,
discourse), the science of time-measurement, has two branches:
Mathematical Chronology, which determines the units to
be employed in measuring time, and
Historical Chronology, of which we here treat, and
which fixes in the general course of time the position of any particular
occurrence, or, as it is generally termed, its date.
It is thus for history what latitude and longitude are
for geography. The first requisite in any system of historical chronology is
an era, that is to say a fixed point of time, the distance from which shall
indicate the position of all others. The term era, the derivation of
which is not certainly known, appears first to have been employed in France
and Spain to signify a number or rule. Since the need of a definite system
of chronology was first recognized by mankind, many and various eras have
been employed at different periods and by different nations. For practical
purposes it is most important to understand those which affect Christian
Foremost among these is that which is now adopted by all
civilized peoples and known as the Christian, Vulgar, or Common Era, in the
twentieth century of which we are now living. This was introduced about the
year 527 by Dionysius Exiguus, a Scythian monk resident at Rome, who fixed
its starting point in the year 753 from the foundation of Rome, in which
year, according to his calculation, the birth of Christ occurred. Making
this the year 1 of his era, he counted the years which followed in regular
course from it, calling them years "of the Lord", and we now designate such
a date A.D. (i.e. Anno Domini). The year preceding A.D. 1 is called
Ante Christum (A.C.) or Before Christ (B.C.). It is to be noted that
there is no year O intervening, as some have imagined, between B.C. and A.D.
It is supposed by many that the calculation of Dionysius was incorrect, and
that the birth of Christ really occurred three years earlier than he placed
it, or in the year of Rome 760 which he styles 3 B.C. This, however, is
immaterial for the purposes of chronology, the first year of the Christian
Era being that fixed, rightly or wrongly, by Dionysius. His system was
adopted but gradually, first in Italy, then in other parts of Christendom.
England would appear to have been among the earliest regions to have made
use of it, under the influence of the Roman missioners, as it is found in
Saxon charters of the seventh century. In Gaul it made its appearance only
in the eighth, and its use did not become general in Europe until after A.D.
1000; accordingly in French the term millésime was frequently used to
signify a date A.D. In Spain, although not unknown as early as the seventh
century, the use of the Christian Era, as will presently be shown, did not
become general until after the middle of the fourteenth century.
Of the chronological systems previously in use it will be
sufficient to briefly describe a few.
The Greeks dated events by Olympiads, or periods
of four years intervening between successive celebrations of the Olympic
games, and this mode of computation, having been largely adopted at Rome,
continued to be frequently used in the first centuries of Christianity. The
Olympiads started from 776 B.C., and consequently A.D. 1 was the fourth year
of the 194th Olympiad.
The Romans frequently reckoned from the traditional
foundation of their city (ab urbe conditâ--A.U.C.), which date, as
has been said, coincided with 753 B.C. They likewise often designated years
by the names of the consuls then in office (e.g. console Planco).
Sometimes the Romans dated by post-consular years (i.e. so long after the
consulate of a well-known man). Naturally the regnal years of Roman emperors
presently supplanted those of consuls, whose power in later times was merely
nominal, and from the emperors this method of describing dates was imitated
by popes, kings, and other rulers, with or without the addition of the year
A.D. It became in fact universal in the Middle Ages, and it subsists in
documents, both ecclesiastical and civil, down to our own day.
The pontifical years of the popes are historically
important (see chronological list in article POPE). Care must be taken, of
course, in the case of such dates, to observe from what point of time each
reign is reckoned. In an elective monarchy like the papacy there is
necessarily an interval between successive reigns, which is occasionally
considerable. Moreover, the reckoning is sometimes from the election of a
pontiff, sometimes from his coronation.
In determining dates by the regnal years of other
sovereigns there are of course various points to which attention must be
paid. Confining ourselves to English history, the earlier kings after the
Norman Conquest dated their reigns only from their coronation, or some other
public exhibition of sovereignty, so that there was sometimes an interval of
days or even weeks between the close of one reign and the commencement of
the next. Only from the accession of Richard II (22 June, 1377) was the
reign of a monarch held to begin with the death or deposition of his
predecessor. Even subsequently to this it was reckoned sometimes from the
day itself upon which the preceding monarch ceased to reign, sometimes from
the day following. Not till the first year of Queen Elizabeth was it enacted
that the former should be the rule. In certain particular instances the
matter was still further complicated. King John dated his reign from his
coronation, 27 May, 1199, but this being the Feast of the Ascension, his
years were counted from one occurrence of this festival to the next, and
were accordingly of varying length. Edward I dated from noon, 20 November,
1272, and in consequence this day in each year of his reign was partly in
one regnal year and partly in another. In the civil wars of York and
Lancaster, Henry VI and Edward IV equally ignored the period during which
his rival assumed or recovered power, and counted their years continuously
onwards from the time when they mounted the throne. Charles II, though he
began to reign de facto only at the Restoration (29 May, 1660),
reckoned his years, de jure, from his father's execution, 30 January,
1648-9, ignoring the Commonwealth and Protectorate. Queen Mary Tudor
reckoned her reign from the death of Edward VI, 6 July, 1553, but the
interval until 19 July of the same year being occupied by the abortive reign
of Lady Jane Grey, public documents in her name commence only with the
latter date. William III and Mary II began to reign 13 Feb., 1688-9, as
"William and Mary". Mary died 28 December, 1694, when the style was altered
to "William" alone; but no change was made in the computation of regnal
years. Within the year, it was long usual to specify dates by reference to
some well-known feast in the ecclesiastical calendar, as, for instance, "the
Friday before Pentecost" or "the day of St. John the Baptist".
In papal and other documents, another epoch is often
added, namely, the Indiction. This had originally been a period of
fifteen years, at the close of which the financial accounts of the Roman
Empire were balanced; but for purposes of chronology the indictions are
conventional periods of fifteen years, the first of which began in the reign
of Constantine the Great. Unlike the Olympiads, the indictions themselves
were not numbered, but only the place of a year in the indiction in which it
fell. Thus indictione quartâ; signifies not "in the fourth indiction",
but "in the fourth year of its indiction", whatever this was. It was obvious
that such an element of computation could serve only to verify more
precisely the date of a year already approximately known. Moreover, the
indictions were calculated on different systems, which have to be understood
The Greek, Constantinian, or Constantinopolitan
Indictions were reckoned from 1 September, 312. These were chiefly used in
The Imperial, Cæsarean, or Western Indictions commenced
with 24 September, 312. These were usually adopted in Western Christendom.
They appear to have been of Anglo-Saxon origin, and to have owed their
popularity to the authority of the Venerable Bede. The day he chose for
the starting point was due to an erroneous astronomical calculation which
made the autumnal equinox fall on 24 September. Further confusion was
caused by the mistake of some chroniclers who wrongly began the
indictional cycle a year late--24 September, 313.
The Roman, Papal, or Pontifical Indictions, introduced
in the ninth century, made the series start from the first day of the
civil year, which was in some cases 25 December, in others 1 January. This
system was also common in Western Christendom, but in spite of its
appellation it was by no means exclusively used in papal documents.
BEGINNING OF THE YEAR
The date at which the year commenced varied at different
periods and in different countries. When Julius Caesar reformed the calendar
(45 B.C.) he fixed 1 January as New Year's Day, a character which it seems
never quite to have lost, even among those who for civil and legal purposes
chose another starting point. The most common of such starting points were
25 March (Feast of the Annunciation, "Style of the Incarnation") and 25
December (Christmas Day, "Style of the Nativity"). In England before the
Norman Conquest (1066) the year began either on 25 March or 25 December;
from 1087 to 1155 on 1 January; and from 1155 till the reform of the
calendar in 1752 on 25 March, so that 24 March was the last day of one year,
and 25 March the first day of the next. But though the legal year was thus
reckoned, it is clear that 1 January was commonly spoken of as New Year's
Day. In Scotland, from 1 January, 1600, the beginning of the year was
reckoned from that day. In France the year was variously reckoned: from
Christmas Day, from Easter eve, or from 25 March. Of all starting points a
movable feast like Easter is obviously the worst. From 1564 the year was
reckoned in France from 1 January to 31 December. In Germany the reckoning
was anciently from Christmas, but in 1544 and onwards, from 1 January to 31
December. In Rome and a great part of Italy, it was from 25 December, until
Pope Gregory XIII reformed the calendar (1582) and fixed 1 January as the
first day of the year. The years, however, according to which papal Bulls
are dated still commence with Christmas Day. Spain, with Portugal and
Southern France, observed an era of its own long after the rest of
Christendom had adopted that of Dionysius. This era of Spain or of the
Cæsars, commenced with 1 January, 38 B.C., and remained in force in the
Kingdom of Castile and Leon till A.D. 1383, when a royal edict commanded the
substitution of the Christian Era. In Portugal the change was not made till
1422. No satisfactory explanation has been found of the date from which this
THE GREGORIAN REFORM
The introduction of the Gregorian Calendar entailed
various discrepancies between the dates which different people assigned to
the same events. The Julian system of time-measurements, introduced by Cæsar,
was not sufficiently accurate, as it made the year slightly too long, with
the result that by the sixteenth century it had fallen ten days in arrear,
so that, for instance, the day of the vernal equinox, which should have been
called 21 March, was called 11 March. To remedy this, besides substituting
an improved system which should prevent the error from operating in future,
it was necessary to omit ten full days in order to bring things back to the
proper point. Pope Gregory XIII, who introduced the reformed system, or "New
Style", ordained that ten days in October, 1582, should not be counted, the
fourth of that month being immediately followed by the fifteenth. He
moreover determined that the year should begin with 1 January, and in order
to prevent the Julian error from causing retardation in the future as in the
past, he ruled that three leap years should be omitted in every four
centuries, viz. those of the centennial years the first two figures of which
are not exact multiples of four, as 1700, 1800, 1900, 2100, etc. The New
Style (N.S.) was speedily adopted by Catholic States, but for a long time
the Protestant States retained the Old (O.S.), from which there followed
important differences in marking dates according as one or other style was
followed. In the first place there was the original difference of ten days
between them, increased to eleven by the O.S. 29 February in A.D. 1700, to
twelve days in 1800, and to thirteen in 1900. Moreover, the period from 1
January to 24 March inclusive, which was the commencement of the year
according to N.S., according to O.S. was the conclusion of the year
previous. From want of attention to this, important events have sometimes
been misquoted by a year. In illustration may be considered the death of
Queen Elizabeth. This occurred in what was then styled in England 24 March
1602, being the last day of that year. In France and wherever the N.S.
prevailed, this day was described as 3 April, 1603. To avoid all possible
ambiguity such dates are frequently expressed in fractional form as 24
March/3 April, 1602/3. In our modern histories years are always given
according to N.S., but dates are otherwise left as they were originally
recorded. Thus Queen Elizabeth is said to have died 24 March, 1603. Not till
1700 was the Gregorian reform accepted by the Protestant States of Germany
and the Low Countries, and not till 1752 by Great Britain, there being by
that time a difference of eleven days between O.S. and N.S. Sweden, after
some strange vacillation, followed suit in 1753. O.S. was still followed by
Russia and other Eastern Orthodox countries well into the twentieth century,
and their dates consequently were thirteen days behind those of the rest of
The Christian Era has this disadvantage for chronological
purposes, that dates have to be reckoned backwards or forwards according as
they are B.C. or A.D., whereas in an ideally perfect system all events would
be reckoned in one sequence. The difficulty was to find a starting point
whence to reckon, for the beginnings of history in which this should
naturally be placed are those of which chronologically we know least. At one
period it was attempted to date from the Creation (A.M. or Anno Mundi),
that event being placed by Christian chronologists, such as Archbishop
Usher, in 4004 B.C., and by the Jews in 3761 B.C. But any attempt thus to
determine the age of the world has been long since abandoned. In the year
1583, however--that following the Gregorian reform--Joseph Justus Scaliger
introduced a basis of calculation which to a large extent served the purpose
required, and, according to Sir John Herschel, first introduced light and
order into chronology. This was the Julian Period--one of 7980 Julian years,
i.e. years of which every fourth one contains 366 days. The same number of
Gregorian years would contain 60 days less. For historians these commence
with the midnight preceding 1 January, 4713 B.C., for astronomers with the
following noon. The period 7980 was obtained by multiplying together 28, 19,
and 15, being respectively the number of years in the Solar Cycles the Lunar
Cycle, and the Roman Indiction, and the year 4713 B.C. was that for which
the number of each of these subordinate cycles equals 1. The astronomical
day is reckoned from noon to noon instead of from midnight to midnight.
Scaliger calculated his period for the meridian of Alexandria to which
Ptolemy had referred his calculation.
Various eras employed by historians and chroniclers may
be briefly mentioned, with the dates from which they were computed.
The Chinese Era dates probably from 2700 B.C., and time
is computed by cycles of sixty lunar years, each shorter by eleven days
than ordinary solar years.
Era of Abraham, from 1 October, 2016 B.C.
Era of the Olympiads, 13 July, 776 B.C., and continued
to A.D. 396 (Olympiad 293).
Era of the Foundation of Rome, 21 April, 753 B.C.
Era of Nabonassar, 26 February, 747, the basis of all
calculations of Ptolemy.
Era of Alexander, 12 November, 324 B.C.
Greek Era of Seleucus, 1 September, 312 B.C.
Era of Tyre, 19 October, 125 B.C.
Cæsarian Era of Antioch, 9 August, 48 B.C., instituted
to commemorate the battle of Pharsalia.
Julian Era, 1 January, 45 B. C., instituted on the
Julian reformation of the calendar.
Era of Spain or of the Cæsars, 1 January, 38 B.C.
Era of Augustus, 2 September, 31 B.C., instituted to
commemorate the Battle of Actium.
Egyptian Year, 29 August, 26 B.C., instituted on the
reformation of the Egyptian calendar by Augustus.
Era of Martyrs or of Diocletian, 29 August, A.D. 284,
employed by Eusebius and early ecclesiastical writers.
Era of the Armenians, 9 July A.D. 552, commemorates the
consummation of the Armenian schism by their condemnation of the Council
Era of the Hegira, 16 July, A.D. 622, dates from the
entrance of Mohammed into Medina after his flight from Mecca; its years
are lunar, of 354 days each, except in intercalary years, of which there
are eleven in each cycle of thirty. In these there are 355 days.
Persian Era of Yezdegird III, 16 June, A.D. 632.
At the French Revolution it was determined to introduce
an entirely new system of chronology, dating from that event and having no
affinity with any previously adopted. In the first form this was the Era
of Liberty, commencing 1 January, 1789. This was soon replaced by the
Republican Era, at first appointed to commence 1 January, 1792, and
afterwards 22 September, 1792. This was the date of the proclamation of the
Republic, which coincided with the autumnal equinox, calculated on the
meridian of Paris. The year was divided into twelve months of thirty days
each, and the days into decades, weeks being abolished. The months had names
given to them according to their seasonal character.
The autumnal months (22 Sept. onwards) were Vendémiaire
(Vintage), Brumaire (Foggy), Frimaire (Sleety).
Winter Months: Nivose (Snowy), Pluviose (Rainy),
Spring Months: Germinal (Budding), Floréal (Flowery),
Summer Months: Messidor (Harvesting), Thermidor
(Torrid), Fructidor (Fruitful).
As these months contained only 360 days, five jours
complémentaires were added at the end of Fructidor, officially called
Primidi, Duodi, Tridi, Quartidi, Quintidi, but commonly known as Sans-culottides.
Olympic or leap years occurred every fourth year of the Republic, and had a
sixth intermediary day called Sextidi. The period thus terminated was called
Franciade. This calendar was enforced in France till 1 January, 1806,
when it was abolished by Napoleon, and the use of the Gregorian calendar
DAYS OF THE MONTH AND WEEK
Various methods have been devised for ascertaining upon
what day of the week any given date falls. The best known is that of
Dominical Letters, which has this disadvantage, that a table is usually
required to find out what is the Dominical Letter for the year in question.
Complication is likewise caused by the necessity of passing from one letter
to another in leap years, on reaching the intercalary day in February. The
following method is free from these inconveniences, and can be worked
without any reference to tables:
The days of the week are numbered according to their
natural order, viz. Sunday=1, Monday=2, Tuesday=3, Wednesday=4, Thursday=5,
Friday=6, Saturday=7. (At the time from which the Christian Era starts there
were of course no weeks, such a measure of time not being known among the
Greeks and Romans. Counting backwards, however, according to our present
system, we can divide all time into weeks, and it is to be noted that in the
Christian period the order of days of the week has never been interrupted.
Thus, when Gregory XIII reformed the Calendar, in 1582, Thursday, 4 October,
was followed by Friday, 15 October. So in England, in 1752, Wednesday, 2
September, was followed by Thursday, 14 September. What we style 14 August,
1907, the Russians style 1 August, but both call it Wednesday.) For our
present purpose the year commences with March; January and February being
reckoned as the 11th and 12th months of the preceding year; thus 29
February, when it occurs, is the last day of the year and causes no further
As a matter of fact, it is found by computation that 1
March of the year known as A.D. 1 was a Tuesday. Assigning to this year the
figure 1 as its year number, to March the figure 1 as its month number, and
adding these to 1, the day number of 1 March, we get 3, indicating Tuesday
the third day of the weeks. From this first datum all the rest follows. The
succeeding days of March increase their figures each by 1, on account of the
increased day number. When 7 is passed it is only the figures which remain,
after division by that number, which are to be considered; thus 11 may be
treated as 4 (7+4) and 30 as 2 (28+2). In general, any exact multiple of 7
(14, 21, 28) may be added or subtracted when convenient without affecting
the result. Instead of adding any number (e.g. 1 or 4) we may subtract its
difference from 7 or a multiple of 7 (e.g. 6 or 3). The remainder 0 in a
division is equivalent to 7, and thus in calculating for the day of the week
it signifies Saturday.
As the days of the leading month, so those of the months
preceding it follow naturally. As March contains 31 days (i.e. 28+3), April
necessarily begins with a day 3 places later in the weekly sequence, and its
month number instead of 1 is 4. So of other months, according to the number
of days in that which preceded. The following are the month numbers
throughout the year which never change:--March 1; April 4; May 6; June 2;
July 4; August 0; September 3; October 5; November 1; December 3; January 6;
February 2. A.D. 1, being a common year of 365 days (or 52 weeks+1 day),
ends with the same day of the week--Tuesday--with which it commenced.
Consequently the next year, A.D. 2, commences a day later, with Wednesday
for 1 March, and as its year number is increased to 2, we get 2+1+1=4. So in
A.D. 3, the year number becomes 3, and 1 March is Thursday. But on account
of 29 February preceding 1 March, A.D. 4, this day falls 366 days (or 52
weeks+2 days) after 1 March, A.D. 3, or on Saturday, and its year number
must be increased to 5; 5+1+1=7. Thus, to find the number belonging to any
year within its own century, we must find how many days beyond an exact
number of weeks there have been since that century commenced. As every
common year contains one day more than fifty-two weeks, and every leap year
two days more, by adding at any period the number of leap years which there
have been in the century to the total number of years in the same, we obtain
the number of days required. To obtain the number of leap years, we divide
the last two figures of the date (i.e. those in the tens and units place) by
four. The quotient (neglecting any remainder) shows the number of leap
years; which, added to the same two figures, gives the number of days over
and above the sets of fifty-two weeks which the years contain. Thus, for
example, the year '39 of any century (939, 1539, 1839, 1939) will have 6 for
its year number; for in such year 48 extra days will have accumulated since
the corresponding day of the centurial year (00), viz. 1 day for each of the
30 common years, and 18 days for the 9 leap years.
One more element of calculation remains to be considered
-- the Century. We begin with the Julian system, or Old Style (O.S.)--according
to which all centuries contain 75 common years of 365 days, and 25 leap
years of 366, and accordingly 125 days in all, over and above 5200 weeks.
But 125 days=17 weeks+6 days. Therefore a Julian century ends with the day
of the week two days previous to that with which if began, and the
succeeding century will begin with the day of the week, one day earlier than
its predecessor. Thus, A.D. 1 March, 1300, being Tuesday, in 1400 it would
be Monday, in 1500 Sunday, in 1600 Saturday. Having obtained the centurial
number for any century, we add to it the year numbers of the years which
follow to the close of that century. Centurial numbers O.S. are obtained by
subtracting the centurial figure or figures (viz. those preceding 00) from
the multiple of 7 next above, the remainder being the number required. Thus
for A.D. 1100 the centurial number is 3 (14-11), for 1500, 6 (21-15), for
1900, 2 (21-19).
Under the N.S. three centuries in every four contain 76
common years and 24 leap years, and thus have only 124 days over 5200 weeks,
or 17 weeks and 5 days, and end with the day of the week three
earlier than they began. The following century, beginning two days earlier
than that which it follows, has its centurial number less by 2. Thus 1
March, A.D. 1700, was Monday, and the centurial number 0 (or 7). 1 March,
1800, was Saturday, and the centurial number 5. Every fourth centurial year
N.S., being a leap year (1600, 2000, 2400, etc.), has 366 days; and the
century to which it belongs, like those of the O.S., diminishes its
centurial number only by 1 from the preceding. N.S. having been introduced
in the sixteenth century, it is only for dates 15-- and upwards that N.S.
centurial numbers are required. They are as follows: for 1500=3; 1600=2;
1700=7; 1800=5; 1900=3; 2000=2. It will be seen that the same figures
constantly recur. Leap year centuries (with the first two figures exactly
divisible by 4) having the centurial number 2, and the three centuries
following having 7 (or 0), 5, and 3 respectively, after which 2 comes round
again. The centurial number N.S. can be obtained from that of O.S. if the
difference of days between O.S. and N.S. be allowed for. This is done by
subtracting the said difference from the O.S. centurial number, increased by
as many times 7 as the subtraction requires. As we have seen, for the
sixteenth and seventeenth centuries, the difference was 10 days; for the
eighteenth, 11; for the nineteenth, 12; for the twentieth and twenty-first,
A.D. 1500 etc.
C. N. (O.S.) = 6
(N.S.) = 3
do. = 5
do. = 2
do. = 4
do. = 0
do. = 3
do. = 5
do. = 2
do. = 3
do. = 1
do. = 2
Rule to find day of week for any date: Take the
sum of the centurial number+year number+month number+day number; divide this
by 7; the remainder gives day of week, O.S. or N.S., according to century
The Astrological Foundation Of
The Christ Myth,
The Astrological Foundation Of
The Christ Myth,
The Astrological Foundation Of
The Christ Myth, Book Two
Astrological Foundation Of The Christ Myth
The Biggest Lie
Biggest Lie Ever Told