Farnesian clock

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The Farnesian clock is an astronomical automaton with clock drive (astronomical clock ), which, according to inscriptions, was commissioned by Duchess Dorothea Sophia Farnese of Parma-Piacenza (1670–1748), built by Bernardo Facini from Venice and completed in 1725. Bernardo Facini (1665–1731) was an astronomer, mathematician and instrument maker in Venice and taught in Piacenza.

The Farnesian clock at a glance.

The astronomical apparatus is now in the Vatican Library (Biblioteca Apostolica Vaticana) after Pope Leo XIII in 1903 . was given for the 25th anniversary of the pontificate.

Total height of the clock: 63.8 cm Octagonal case box: Outside diameter across the corner: 42 cm; across the outside: 38.9 cm

The watch is famous for several reasons:

  • It is an outstanding testimony to the planning and execution of an astronomical clock in the early 18th century, because it was the first attempt to solve the problems of time measurement that were then pending in a single work.
  • It stands for a completely new way of the art of watchmaking ( watchmaker ), in which complex speed ratios are transferred to the displays on the dial. Ludwig Oechslin's scientific documentation provides detailed information on the technical details of the display and drive mechanism .
  • Although the work and its individual parts were described and recorded in drawings by Nicolo Anito in 1796, these are not sufficient to understand how the machine works. With archaeological care and methodology, Ludwig Oechslin disassembled the defective watch into its 462 individual parts and repaired it. He described the mechanical work in a unique scientific opus, which is divided into three volumes:
  1. A technical description, an interpretation and historical classification as well as a documentation of the work of Nicilo Anito are given in a text section.
  2. A catalog contains the rotating parts, the auxiliary parts and a bibliography and name register.
  3. In the third volume there is an illustration: drawings by Nicolo Anito, photos of all individual parts of the watch as well as numerous additional drawings for the text, catalog and description.

With this work, Ludwig Oechslin gives anyone interested the opportunity to study every detail of the complicated mechanism for themselves, which is therefore not described in detail here.

The problems of time measurement in the early 18th century were a) mathematical and astronomical as well as b) mechanical and manual nature. They concerned in detail

  1. The search for how the stars of the universe ( planets , stars and constellations ) explored at that time can be represented analogously to their movement in a display limited by mechanical conditions.
  2. The representation of the stars in relation to the civil / civil time display ( clock ).
  3. Maximizing the precision of such astronomical and civil time displays.
  4. The manufacture of ever more accurate timepieces ( timing ) to solve the length problem.
  5. The guarantee of functionality even when the watch is moved.
  6. To make clocks run as noiseless as possible.
  7. Ensuring that the time is displayed even in the dark.

With the Farnesian clock, Bernardo Facini made an important contribution to solving these problems.

The displays of the Farnesian clock

In the present clock , the earth was chosen as the imaginary center point ( geocentric view of the world ). The largely correct reproduction of the movement of the sun and moon has been bought at the price of renouncing the planetary movements. The illustration of the sun and the moon (apparently) revolving around the earth as well as the restriction to these three celestial bodies allows a representation of their mutual movements that does not contradict the findings of Nicolaus Copernicus .

The displays of the clock can be divided into civil displays and astronomical and astrological displays.

1. Civil ads

2. Astronomical and astrological displays

The aforementioned displays are made possible by a combination of six, partly movable, different display zones, by three further circular displays with pointers, by the clock hands, the movable sun hand, movable display arms and by windows.

The six display zones and the pointing instruments

The dial of the watch is divided into six display areas.

From the outside in, these are:

1. Zone: A golden number ring to indicate the astronomical time (immobile): Division into three zones:

  • The outermost zone is divided into 4 × 90 ° = 360 ° units. Starting point at the VI. Hour of the middle zone, so that the 90s meet at the zenith (lat. Meridies, noon) and nadir (lat. Media nox, midnight).
  • The middle zone is divided into 2 × 12 = 24 hours with Roman numerals. The beginning is clockwise at the zenith and at the nadir.
  • The innermost zone divides the second zone into halves, quarters and eighths.

2. Zone: A movable silver number ring for the indication of the Italian time. Division into three zones:

  • The outermost zone divides the middle zone into half, quarter and eighth.
  • The middle zone is divided into 2 × 12 hours with Roman numerals. Indication of halves by ornament.
  • The innermost zone contains Latin text information: at VI. Hour at the zenith arcus diurnus (day arc) and at the nadir arcus nocturnus (night arc). Additional inscription: The Italian time in its true indications ( horae italicae in veris motibus )

3rd zone: rotating astronomical display zone with starry sky, ecliptic , equator and days of the year.

  • Outer ring with 360 ° graduation for the equator
  • Star zone with display of the fixed stars , 89 individual stars , names of the 29 constellations shown ; Indication of the zodiac only in symbols; List of constellations and stars according to their passage at the sun in the course of a year in a counterclockwise direction; Table for alphabetical listing of the constellations with information on the star names, information on the number of stars in a constellation, information on the position in the constellation, planet names and expansion in degrees on the display.
  • Circlet with Latin texts and signs for spring equinox , autumn equinox ( equinox ), summer solstice , winter solstice
  • Date-ready ( Julian year ) divided into four zones: ad) 12 × 30 ° = 360 ° of the ecliptic , bd) Latin lettering for the zone ad, cd) Reproduction of the date according to days of the month with indication of 365.25 days in the year, dd) Labeling for the zone cd, the tens and the last of the month indicated. At the beginning of the month the name of the month is engraved in Latin.

4. Zone: A rotating red circlet with the knot signs for the ascending and descending nodes of the moon. The point at which the moon's orbit crosses the ecliptic from north to south is called the descending knot. The point at which the moon's orbit crosses the ecliptic from south to north is called the ascending node. The position of the ascending node in relation to the vernal equinox is one of the six orbital elements that are necessary for a complete description of a Keplerian planetary orbit . This hoop rotates once every 18.61 years in relation to the astronomical display zone and thus corresponds to today's observation data.

5th zone: The rotating moon display zone is the widest zone and is divided clockwise into 59 half and thus into 29 ½ whole units (number of days of the synodic month ( synodic period ), time span between two identical moon phases) around the stand of the moon. Starting from 29 ½, a square, an equilateral hexagon and an equilateral triangle are drawn in, the corner points of which indicate the angle at which the sun is to the moon (aspect). This shows: conjunction 0 ° (new moon), opposition 180 ° (full moon), square 90 ° or 270 ° (1st and last quarter moon), trine 120 ° or 240 ° (1st and last third), sextile 60 ° or 300 ° (1st and last sixth). On the moon display zone there is a number ring at 29 ½, which is divided into 4 × 90 = 360 °. It has a round opening towards the outer edge, in which a two-colored moon ball visibly shows the phases of the moon. A little to the right of it is another dial engraved on which the respective day of the synodic month is displayed again.

6. Zone: In the center of the clock is the immovable dial for Spanish time. This zone contains the information necessary in daily life for hours (12 hour display with Roman numerals) and minutes of the day , days of the week (Sol, Luna, Mars, Merc., Jupit., Venus, Satur.) ( Weekday ) in a lower one Window, month and year . In addition to a Latin inscription, the dial contains another window for the date display along the minute display (date). The current month name (month) appears in the window. The name of the month (in abbreviated form and associated zodiac sign) and the date (in an extension of the window) are engraved on a bracelet. Reproduction of the Julian year. The division is made in 365.25 days, recorded in a spiral, four turns from the outside to the inside. The outermost turn is divided into 366 days, the three others into 365 days. With the last day, the outermost turn reaches ¾ units beyond the beginning of the spiral, the divisions on the following spirals remain behind the day with the same date on the preceding spiral by ¼ units, so that after the inner three turns the beginning and end of the spiral coincide at the same level. Days with the same date are connected by dashes. Because of their quarter-shift from turn to turn, these are at an angle to the diameter of the hoop. Buckling of these lines from the second to the outermost turn from January 1st to February 29th due to insertion of the switching day and thus ¾ units of excess length of the outermost turn. The spiral does not tapers continuously, but is circular. However, it moves to the next level from December 25th to January 5th. The whole thing represents a successful solution to the leap year , which is read as the extreme on the last spiral. The 10th, 20th and the last day of the month are marked with numbers within the last spiral date. The clock cannot be understood without the hands and indicator arms, which are explained below.

In the center of the clock, as with every clock, we find the large and small hands for the hours and minutes of Spanish time.

To the right and left of the dial of zone 6 there is a main indicator arm

  • for length of day, sunrise
  • for length of day, sunset

each with a secondary display arm, which is at an angle of 30 ° to the center of the display. In other words: there is a 1 hour difference from main arm to side arm on the dials for Italian and astronomical time. The inscription "Twilight" ( crepusculum ) is on the branch of the ascent (ortus ); on the branch of the setting ( occa.us ) the inscription “end of twilight” ( finis crepusculi ). The two main arms reach over the outer 5 zones and mark the horizon of the observer in connection with the movement of the stars, so that either rising or setting of the same can be observed on them. The arms for sunrise and sunset adapt to the annual cycle of day and night lengths by increasing or decreasing the day or night arc of the sun. The dial for the Italian period is connected to this arm and follows its movement. Since the lengths of day and night and their differences vary over the course of a year with the geographical latitude on which the watch and the observer are located, Facini had to ensure that the latitude on which the watch is located could be set is. Indeed, a setting can be made for latitudes between 31 ° and 52 °.

The sun pointer is located above zone 2-4 of the dial, a structure with two points on the outside and one on the inside. Text to the middle pointer outwards: True movement ( motus verus ); Text to the shifted pointer far left: Bourgeois time ( cives horae ). You can also see a round glass stone set as a symbol of the sun. Above it is a scale from 43 to 60 and from 0 to 15, for a total of 32 units. These are minutes to indicate the deviations of the true from the mean solar time, which can range from −14 min 24 s to +16 min 21 s based on the equation of time "true time minus mean time". The Latin text on the left and right of the scale explains the meaning of the scale: compensation of natural days ( aequatio dierum naturalium ), i.e. H. the deviation of the true solar time from the mean. The middle outer hand shows the true movement of the sun, i.e. the astronomical time, while the second outer arm, which is offset counterclockwise, is intended for reading the Italian time. For the Italian time there is another equation of time , which is: True solar time + horizon time shift compared to mean time = Italian time equation.

Between zone 6 and zone 5 there is a minute number ring for the astronomical time.

The minutes of Italian time are indicated on a further number ring on the right, which sits on the main display arm for day length, which extends over the five outer zones.

Appreciation of the watch

The endeavor to bring the above-mentioned pending problems of time measurement closer to a solution in a single work in the early 18th century is the characteristic and unique feature of the Farnesian clock. Since manual problems of watchmaking and astronomical and mathematical problems come together here, their solution is complex. What is striking is the careful and thorough planning of the astronomical part, where meticulously and mathematically a rendition and abstraction of celestial phenomena was found, which the layperson was bound to be amazed at. In contrast, the art of watchmaking in the present watch falls off a bit, which requires a lot of practical, kinematic and physical experience. Nevertheless, the Farnesian clock surpasses the previous one in the complexity of the arrangement and the refinement of the displays and gears. Complex speed ratios are transferred to the display of the dial in a completely new way. The independently rotating maturity, such as B. Sun pointer, astronomical display or moon display zone get their movement eccentrically on the outskirts via gear rings attached to them with large numbers of teeth. The gain in accuracy is considerable. The overall view of the presented time events is unique at this time.

Ludwig Oechslin appreciates the watch as follows: "The performance of the Farnesian watch is therefore the precision and synthesis of the most varied of information that cannot otherwise be found on the same dial." (Volume 300, p. 120)


  • Ludwig Oechslin : The Farnesian clock: the astronomical automaton by Bernardo Facini and the drawings by Nicola Anitos in the Vatican Library, Città del Vaticano: Biblioteca Apostolica Vaticana , 1982; 3 vols .: Ill. Series Studi e Testi Volume 300; Volume 301.1; Volume 301.2; Volume 302, ISBN 88-210-0524-0