Hours and Hours

I found myself wondering how time during the day was broken up into hours.  Noting the cycle of light and dark during days is pretty simple: every culture and every language as far back as I’ve been able to find has had the concept of daylight time and darkness time.  But how did the current scheme of 24 hours in a day, each hour with 60 minutes and each minute with 60 seconds, develop?  A second question that follows from this is, were other schemes considered, if so what were they, and why were they discarded?

Herodotus (c.490 BC to c 425-20 BC), in The Histories, Book 2, 109, adds an aside in his discussion of how Egypt developed geometry:

I think this was the way in which geometry was invented, and passed afterwards into Greece – for knowledge of the sundial and the gnomon and the twelve divisions of the day came into Greece from Babylon.1

Earlier in The Histories, Herodotus credits the Egyptians with the year (as quoted in the earlier post, Marking Time (or at least calibrating it)):

As to human matters, they all agreed in saying that the Egyptians by their study of astronomy discovered the year and were the first to divide it into twelve parts…the Egyptians make the year consist of twelve months of thirty days each and every year intercalate five additional days, and so complete the regular circle of the seasons.2

Egyptians and Babylonians, two of the earliest city civilizations, then, are responsible for some of the earliest time measurements, at least according to Herodotus.  They may be responsible for the earliest standardized time measurement, but I suspect that others before the formation of city civilizations could have started the process, and my guess is that the process had progressed sufficiently that some of the standardized concepts were not original with the Babylonians and Egyptians.

Pliny the Elder (23 AD to August 25, 79 AD3), in Natural History, has a slightly different take. In Book 2, Chapter 78, he states that the first sundial was made by Anaximenes the Milesian and was exhibited for the first time in Lacedaemon.  However, it is not clear in this first mention whether Anaximenes’s sundial was set up to measure hours, but later in Natural History, in Book VII, Chapter 60, Pliny states:


…[I] have already stated, in the Second Book, when and by whom this art was first invented in Greece; the same was also introduced at Rome, but at a later period. In the Twelve Tables [the foundation of Ancient Roman law], the rising and setting of the sun are the only things that are mentioned relative to time. Some years afterwards, the hour of midday was added, the summoner of the consuls proclaiming it aloud, as soon as, from the senate-house, he caught sight of the sun between the Rostra and the Græcostasis; he also proclaimed the last hour, when the sun had gone down from the Mænian column to the prison. This, however, could only be done in clear weather, but it was continued until the first Punic war. The first sun-dial is said to have been erected among the Romans twelve years before the war with Pyrrhus, by L. Papirius Cursor, at the temple of Quirinus,…

M. Varro says that the first sun-dial, erected for the use of the public, was fixed upon a column near the Rostra, in the time of the first Punic war, by the consul M. Valerius Messala, and that it was brought from the capture of Catina, in Sicily: this being thirty years after the date assigned to the dial of Papirius, and the year of Rome 491. The lines in this dial did not exactly agree with the hours; it served, however, as the regulator of the Roman time ninety-nine years, until Q. Marcius Philippus, who was censor with L. Paulus, placed one near it, which was more carefully arranged: an act which was most gratefully acknowledged, as one of the very best of his censorship. The hours, however, still remained a matter of uncertainty, whenever the weather happened to be cloudy, until the ensuing lustrum; at which time Scipio Nasica, the colleague of Lænas, by means of a clepsydra, was the first to divide the hours of the day and the night into equal parts: and this time-piece he placed under cover and dedicated, in the year of Rome 595; for so long a period had the Romans remained without any exact division of the day.4

It appears, then, from Pliny, that the concept of “hour” was part of the Roman way of thinking.  There is a clepsydra mentioned for measuring the hours of the day and  night into equal parts.  “Clepsydra” is the name given to “water clocks”, which are usually bowls or basins with drains that are periodically filled or re-filled with water, and that drain at a predetermined rate.  The amount of water remaining was representative of the time.  But it looks as if, from Pliny’s article, that the hours of the day were divided into equal parts, and those of the night as well, but relying on the length of the day light by the season.

There is mention of a sundial in the Bible, in II Kings, Ch. 20, verses 9 – 11.  Isaiah refers to it to prove that the Lord is as good as his word to Hezekiah, by having the Lord make the shadow thrown by the gnomon move backwards by 10 degrees.  Hezekiah then believes.  I do not know the dates or chronology of the prophets or of the writing of the Bible well enough to say whether this occurred before Anaximenes or later, or if this is an artifact of translation: I have a King James version, which was translated in the early 1600’s.

In a very thorough book, History of the Hour, by Professor Gerhard Dohrn-van Rossum, the hour is described as basically having two separate conceptions from fairly early on.  He states that by the time of Christ’s birth, there was a division of the 24 hours into equal hours, but it was largely used by astrologers for horoscopes.  Otherwise, the Babylonians had divided the day into hours which varied: day time and night time were divided into 12 hours each, which meant that during the summer in Babylon and further north on the globe, the daylight hours were longer and in the winter, they were shorter.  The inverse happened to the night time hours: when daylight hours were longer in the summer, the hours of nighttime darkness were shorter and during winter nights, the hours were longer:

These hours were called temporal hours, “horae inequales.”  Expressed in minutes – which were unknown at the time – the ratio of the longest to the shortest daylight hour in Upper Egypt was 67:53, in Athens 73:47, in Rome 76:44, in southern Germany 80:40, in northern England 90:30.5

To work with these ratios, which represent the ratio of minutes of daylight at the summer solstice to the minutes of daylight at the winter solstice, by multiplying and finding map locations we get the following table.  At the times of the equinoxes, when the daylight time and nighttime darkness hours are equal, there are 720 minutes of daylight and 720 of darkness:

City approx. Latitude Summer Daylight Winter Daylight
Alexandria 30o 804 minutes 636 minutes
Athens 38o 876 minutes 564 minutes
Rome 42o 912 minutes 528 minutes
Munich 47o 960 minutes 480 minutes
Newcastle 55o 1080 minutes 360 minutes

So, the further north one goes, the longer the daylight hours in summer and the shorter in winter, until one reaches the Arctic Circle, which is the line above which there are days in the summer when the sun does not set at all, and there is a time in the winter when the sun never rises above the horizon: darkness for several months.

In Newcastle in winter, one would have 6 of the equal hours to accomplish a day’s worth of tasks, essentially 12 segments 30 minutes long in the terms of the temporal hours.

There was a third division of the time during the middle ages for Christians, which is discussed in a number of places, including the book by Professor Dohrn-van Rossum.  These were defined times at which to perform the daily round of devotional prayers.  These were the hours that were used by monasteries for determining when the monks were to gather to pray.  At some point, the procedure changed from having one of the monks being designated the timekeeper, whose job it was to awaken the monks in the night and to call the monks during the day, to giving the job over to bells that were rung.  In the 13th century, the earliest attempts were made to have a mechanical device ring the hours.  Professor Dohrn-van Rossum states “…that the combination of bell striking mechanisms with large water clocks is known around 1250…”6

By 1250, Chinese astronomers had created water-driven globes and armillary spheres.  These used water to power the mechanics rather that operating like the clepsydra.   The earliest mechanical clock, according to Joseph Needham, was completed in 725 AD, and was an astronomical instrument powered by water which also served as a clock.  The purpose of the astronomical instrument/clock was to time accurately the hours of conceptions of the Emperor’s children, that is, sons, so that the court astrologers could determine which of the sons had the most auspicious horoscope and should become the next emperor.

A successor instrument was built by Chang Ssu-Hsun in 976 AD, using mercury instead of water to power it, because mercury would not freeze in the middle of a cold night.  The most notable astronomical instrument/clock was built in 1092 by Su Sung.  It is notable in that it did use water again for power, and although it was destroyed by a following dynasty, because of extensive plans and drawings that have survived, a replica has been built which resides at the Science Museum in London.  It is possible that the rumors of these mechanical clocks with a form of escapement reached Europe, but the links are not certain and are tenuous at best.7

However, the work on establishing hours continued in Europe: King Alfonse X of Spain commissioned the Alfonsine Tables, based on a translation of Ptolemy’s tables, which then were used from the time they were completed during his reign from 1252 to 1284 AD.  Copies were made and circulated among the intelligentsia, and the Tables were first printed in 1483.  They were the standard tables for astronomers until the Rudolphine tables, based on the work of Tycho Brahe and finished by Johannes Kepler, were published in 1627.  In the Alfonsine tables,

…hours were divided into minutes, seconds and “terciae”, …[d]espite the ambiguous terminology, the rapid and broad diffusion of the tables must have promoted knowledge of the hour-minutes and hour-seconds in learned circles8

There is a passage in the Roman de la Rose, composed between 1275 and 1280, which alludes to something resembling mechanical clocks, but does not appear to be as clear as one might wish.  However by 1315 to 1320, there are two references to “clocks” in Dante’s Divine Comedy that could only be written if the author knew a little bit about clocks.

Then as a clock tower calls us from above
when the Bride of God rises to sing her matins
to the Sweet Spouse, that she may earn his love,

with one part pulling and another thrusting,
tin-tin, so glad a chime the faithful soul
swells with the joy of love almost to bursting-

just so, I saw the wheel of glories start
and chime from voice to voice in harmonies
so sweetly joined…

Paradiso, Canto X, ll. 138-147

So spoke Beatrice, and those blissful souls,
flaming as bright as comets, formed themselves
into a sphere revolving on fixed poles.

As the wheels within a clockwork synchronize
so that the innermost, when looked at closely
seems to be standing, while the outermost flies;

just so those rings of dancers whirled to show
and let me understand their state of bliss,
all joining in the round, some fast, some slow.

Paradiso, Canto XXV, ll 10-18 9

I have included a list of the third division of time, the devotional hours, which comes from the commentary included in a facsimile edition of The Hours of Jeanne D’Evereux, Queen of France, published by The Metropolitan Museum of Art, in New York.  The commentary was done by James J. Rorimer, Director of the museum, though the date of his notes is not given.  The facsimile was published originally in 1957, reprinted several times, with the last date given as 1973.

Hour name Occurs
Matins Midnight
Lauds Sunrise
Prime 6:00 a.m.
Terce 9:00 a.m.
Sext Noon
None 3:00 p.m.
Vespers Sunset
Compline 9:00 p.m.

In the commentary, Rorimer dates the creation of the book to no earlier than 1325, when Jeanne and King Charles IV of France were married, and no later than 1328, when King Charles died, since the book was a gift from him to her.  If the commentary is correct, the devotional hours were measured by clock hours, by equal hours, in the early 14th century.  There appears, from the Dohrn-van Rossum book, to be some question about when the actual adoption of equal clock hours occurred, but was no earlier than the late 13th century, when the first mechanical “clocks” were set up built, originally to ring bells.

Clocks did not get faces until later in the 14th century.  I am including pictures of the clock at Salisbury Cathedral, originally installed in 1386.

The clock with its descriptive sign first appeared in the post, A Slight Digression.

Outside of Salisbury Cathedral is another form of clock: a sundial, evidently set up in about 1749.  The sundial does indicate the hours: the picture was taken on a sunny day at about 5:00 in the afternoon.  The gnomon is not solid: it has one end of the pointer at the apex of the hour lines, and a support that is curved sitting just above half-way near the noon line.  The shadow of the indicator is just about at five (V).

The sign accompanying the sundial discusses another of the peculiar ways that time was measured: the Julian Calendar had shifted the seasons far enough out of synch that a major correction had to be made, which was done in England in 1752, and at other times in other parts of Europe.10

During the 14th century, one of the questions was when to start the day.  We are familiar with the start of the day at midnight – 12:00 AM, 0:00 (zero o’clock on a 24 hour clock, or 24:00).  But some started the day at sunrise, and others started at sundown.  Some used a 24 hour clock, and some divided the day into 2 – 12 hour segments.  Among the Jewish and the Islamic religions, sundown is the start of various holidays.  Those that started at sundown designated any events that happened at night as happening during the succeeding day, while those which started at sunrise included the night’s events of the night following the day.  Until the “standard” was accepted to start the day at midnight, only Roman jurists, and those using the devotional scheme with the start of the day at Matins, used midnight at the dateline.   I have not found an exact date or event, but this became customary during the later 14th century.

Along with when to start the day was the question of how to design the faces of the clocks.  Some went with a 24 hour face, most with a 12 hour face.  St. Mark’s Cathedral in Venice chose to use a 24 hour face, but put I and XXIIII in the place where we are accustomed to seeing 3:00.

The first clock housed in the tower was built and installed by Gian Paulo and Gian Carlo Rainieri, father and son, between 1496 and 1499, and was one of a number of large public astronomical clocks erected throughout Europe during the 14th and 15th centuries. The clock has had an eventful horological history, and been the subject of many restorations, some controversial.

After restorations in 1551 by Giuseppe Mazzoleni, and in 1615, by Giovanni Battista Santi, the clock mechanism was almost completely replaced in the 1750s, by Bartolomeo Ferracina. In 1858 the clock was restored by Luigi De Lucia. In 1996, a major restoration, undertaken by Giuseppe Brusa and Alberto Gorla, was the subject of controversy, amid claims of unsympathetic restoration and poor workmanship.11

In the earlier post, Surveying and Mapping, I mentioned a timekeeping scheme developed during the French Revolution, with 10 hours per day, 100 minutes per hour and 100 seconds per minute: it never gained many adherents and was dropped when Napoleon reached his accord with the Church.

With the advent of the mechanical clock and the ability to measure hours equally rather than using the temporal hours based on sunrise and sunset, the pace of mechanical invention quickened as the regulating by the clock of work, tasks, and daily events proliferated and permeated all of Europe and ultimately the rest of the world.  The mechanical clocks led to the prevalence of the clockwork universe model.  Hours were divided into minutes and seconds, and the tools to measure those further divisions were developed.  The tools are now so sophisticated that the term “nanosecond”, one billionth of a second, is a commonplace term.  I still have trouble, though, imagining the experience of a tenth of a second.

1 Herodotus, The Histories, Penguin Books, London, England.  Translated by Aubrey de Selincourt, 1954. Revised edition, 1972.  Revised edition with new introductory matter and notes by John Marincola 1996, further revision 2003. P. 136.  I had found so many “measurement” references to Herodotus that I bought a copy and am reading it.  Since Herodotus died around 425 and 420 BC, the book is surprisingly lively for 2400 years old.

2 Herodotus, The Histories, Penguin Books, London, England.  Translated by Aubrey de Selincourt, 1954. Revised edition, 1972.  Revised edition with new introductory matter and notes by John Marincola 1996, further revision 2003. P. 96.

3 The date of Pliny the Elder’s death is quite precise: he was killed trying to rescue a friend and his family during the eruption of Vesuvius.

4 Pliny the Elder, Natural History, Book VII, Chapter 60, Second English translation by John Bostock and H.T.Riley, 1855; complete, including index, found at:


5 Dohrn-van Rossum, Gerhard, History of the Hour, Clocks and Modern Temporal Orders, translated by Thomas Dunlap, University of Chicago Press, Chicago, Ill, 1996. P.19.

6 Dohrn-van Rossum, Gerhard, History of the Hour, Clocks and Modern Temporal Orders, translated by Thomas Dunlap, University of Chicago Press, Chicago, Ill, 1996. P. 71.

7 Information about the Chinese astronomical instruments comes from Temple, Robert, The Genius of China, 3,000 Years of Science, Discovery & Invention, Inner Traditions, Rochester, VT., 1986,1998,2007.  The introduction was written by Dr. Joseph Needham, and the material was drawn from Needham’s epic multi-volume work, Science and Civilization in China.

8 Dohrn-van Rossum, Gerhard, History of the Hour, Clocks and Modern Temporal Orders, translated by Thomas Dunlap, University of Chicago Press, Chicago, Ill, 1996. P. 81

9 Dante Alighieri, The Divine Comedy, Rendered into English Verse by John Ciardi, W.W.Norton & Company New York, N.Y 191, 1965, 1967, 1970, 1977.

10 Big thanks for the Salisbury clock and sundial photos to my daughter, Branwyn Darlington.

11 http://en.wikipedia.org/wiki/St_Mark%27s_Clock

Both the picture and the quote are from the Wikipedia entry for St. Mark’s Clock.

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