Snapshots on the works and life ofGiovanni Dondi

Distinguished Italian Clockmaker

Prof. Ettore PennestrìUniversità di Roma Tor Vergata

December 2008Seminar for the visiting

Students of the Board of European Students of Technology

Outline

• Jacopo Dondi – Clock at Palazzo dei Carraresi• The Ptolemaic model• Giovanni Dondi• The Tractatus Astrarii• Work on virtual clock reconstruction

The place and the historical period

• The Dondi family is original from the city of Chioggia and lived in Padova and Pavia at the end of XIVth century

Chioggia, Padova, Venezia

Short biography of Jacopo Dondi (1298-1355)

• Born in Chioggia on from Isacco Dondi• Practiced medicine first in Chioggia and then

in Padova where he was professor of mathematics, logic and astronomy at University of Padova

• In 1344 he designed an astronomical clock installed in Piazza dei Signori in Padova

Jacopo Dondi’s astronomical clock

The astronomical clock ofPalazzo dei Carraresi in Padova

• It’s one of the first astronomical european clocks• It was installed in Palazzo dei Carraresi in 1334• In 1399 the clock was destroyed during the siege of

Venetians• Was rebuilt by 1424 by Novello Dondi, son of

Giovanni Dondi • From this clock one can read time (hours), the moon

phases and the position of the sun within the zodiac.

Something unusual…• There are 11 symbols of the

zodiac.• The place of the sign Libra is

almost taken by the sign of Cancer (The Crab)

• It seems that this was a Jacopo Dondi’s protest for a town without justice due to the hard ruling of the Carraresi family.

Why was Jacopo Dondi’s work so important?

• In the Middle Age astronomy was one of the most important sciences.

• Astronomy and astrology could not be separated in the Middle Ages as they are today.

• For the educated medieval man or woman both the movement of the heavenly bodies and their effect on man were entirely natural and subject to scientific study and prediction.

Why was Dondi’s work important?

• Jacopo and Giovanni Dondi were among the first Europeans to design and build astronomical clocks (astrari).

• Through an astrarium one could follow at a glance the motion of planets and thus make predictions on future.

Astronomy

• The interest in this science increases with the translation by the monk Gerardo of Cremona (1114-1187) of the Almagest, the astronomical treatise originally written by the Greek astronomer Ptolemy of Alexandria (II a.C.)

Few words about Ptolemaic astronomy

• The ancient philosophers imagined the universe consist of concentric crystalline spheres, nested inside one another, which carried the sun, moon, and planets in their motions.

• Astronomers tried to obtain geometrical schemes that would allow them to make accurate predictions of the motions and future positions of celestial bodies.

A fundamental text in astronomy: Almagest

• Ptolemy devised a geometrical scheme in an effort to explain the variations in the apparent speeds of the planets.

• Some say that he knew that his model was only system with many parameters to descri-be astronomic phenomena: Mathematical Sintaxis or Almagest.

The Ptolemaic model

The Ptolemaic cosmological model

How Giovanni Dondi mechanically reproduced this motion in his Astrarium?

Biography of Giovanni Dondi• Giovanni Dondi was born in Chioggia about 1330;• In 1343 moved with his father to Padova; • In 1355 was member of Collegio Dei Dottori nelle Arti e nella

Medicina • In 1359 received the title of Doctor in Phylosophy and

Astrology .• About 1368 he had a teaching position at University of

Bologna.• Because of arguments with Francesco da Carrara, lord of

Padova, in 1379 moved to Pavia where Galeazzo II assigned him a teaching position at the university.

• Died in Pavia on October 1388

It is not clear if the right to modify the name in Dondi dell’Orologio (de Dondis ab Horologio) was given to the father Jacopo or to the son Giovanni.

Adsit Initio Deus Medium ComiteturEt Opus Propositum Ducat in Finem

Tractatus Astrarii Johannis De Dondis Paduani Civis

Cui Tres Sunt Partes

• The Tractatus Astrarii describes in detail the design and the building phases of the Astrarium.

• The actual building of the Astrarium required about 16 years (1365-1381).

Astrarium

• The astrarium stood about 1 m high

• Consisted of a seven-sided brass or iron framework resting on 7 decorative paw-shaped feet.

Clock description

• Dondi constructed the clock with its 107 gear wheels and pinions entirely made by hand. • No screws were used, and every part was held together by over 300 tapering pins and wedges, with some parts being soldered. • Most of the wheels have triangular shaped teeth, although some are blunt-nosed.

The calendar wheel• A simple wheel train turned a dial marked on the margin with a scale of 24 equal hours and 10 minute intervals. • The dial rotated ccw against a fixed pointer.• On each side of the clock dial was a fixed plate or 'tabula orientii', graduated with months and days of the Julian calendar • The astrarium gives the times of the rising and setting of the mean sun for the latitude of Padua.

The seven dials

The verge escapement mechanism

Dondi’s astrarium was one of the first mechanical clocks to use the verge escapement. This was a striking advance in clock construction.

The verge escapement

An escapement is a mechanism which allows the teeth of gears to “escape” one at a time, providing periodic energy impulses to the balance. French and English clockmakers from the late 1300s onwards used Dondi’s methods to construct this device.

The foliot verge escapement

Directly above the 24 hour dial is the dial of the

Primum Mobile reproduced the diurnal motion of the stars and the annual motion of the sun in the zodiac.

In medieval and Renaissance astronomy, the Primum Mobile, or "first moved," is the outermost moving sphere in the geocentric model of the universe.

Primum

mobile

24 h = 86400 s

The planetary dials

Each of the planetary dials used complex clockwork to produce reasonably accurate models of the planets' motion. These agreed reasonably well both with Ptolemaic theory and with observations..

Jupiter

Mars

Moon

Mercury

Saturn

Venus

Dondi used noncircular gear wheels, in order to more accurately model the irregular motions of the planets

What is so extraordinary in Giovanni Dondi’s work?

• From the engineering point of view the design and construction of such mechanical complex devices appears an extraordinary achievement even for today standards.

• The construction of an astrarium requires a deep knowledge of astronomy and outstanding mathematical and mechanical skills.

• It is a great example of the (almost forgotten at the time) Hellenistic scientific methodology of studying the nature through mathematical and/or mechanical models.

• Through manuscripts Giovanni Dondi fully documented the design and building of his astrarium.

Where was the Astrarium installed?• The Visconti family, who were patrons of

Giovanni Dondi, acquired his astrarium and installed it in a library at the Castello Visconteo of Pavia.

Galeazzo II Visconti

• (1320-1378)• He considered the

astrarium as a strategic weapon. He was totally confident on the capability of the Astrarium to foresee the future.

What happened to the Astrarium?

• The Astrarium remained in Pavia until 1440 .• That year the Astrarium needed a repair, but nobody was able to do the work.• A Dutch clockmaker Zelandenus repaired it.

Charles V • In 1529 the emperor Charles V

saw the Astrarium abandoned in a room of the castle of Rosate.

• He commissioned a working replica of the Astrarium to the Italian clockmaker Gianello Torriano. The working replica was transported in Madrid were was destroyed by fire.

The astrarium was prized as one of the most remarkable and beautiful artifacts of its time and was said to have been studied by Leonardo da Vinci, Regiomontanus, and Petrarca.

Was Dondi’s work inspired by others?

Richard of Wallingford (1292-1336) Abbot of St.Albans (England) designed and documented in a manuscript the construction of an astrarium.

Was Giovanni Dondi aware of this work?

Chioggia, 30 Novembre 2005

• In the book "English church clocks: 1280-1850" authored by C.F.C. Beeson, at pag. 20 one reads:

• "Three Lombards the clockmakers who made the clock, arrived Windsor with their tools on the 8 April 1352 and stayed for 6 1/2 weeks boarding at the table of Stephen Chesebury. By Whitsun the clock seems to have been finished in working order and the Lombards left on 24 May and presumably returned to Italy. The king did not instal another clock until 1366."

Open questions• Who are these lombards that in 6 weeks install a clock that works in a satisfactory manner for many years ?• Why there is the doubt that they came back to Italy ?• Why are they called lombards?• Two of them could be Jacopo and Giovanni Dondi ?• The visit of the lombards is 1352 and in 1356 the Astrarium in St. Albans is finally completed. • The Dondi family were builders of mills and the abbey of St. Albans was the most advanced English center in this field. • Jacopo Dondi wrote a book on tides. In St. Albans there was a tidal clock. Was Jacopo Dondi motivated by the view of the strong tides in England?• Richard de Bury (friend of Richard of Wallingford) Petrarca (friend of Dondi), Marin Faliero (friend of Dondi) knew each other very well while in Avignon (France). Did they spoke each other of their outstanding friends clockmakers?

Builders of Astrarium replicas

• Alan Lloyd – England (1960)• Luigi Pippa – Italy (1978)• Emmanuel Poulle – France (1989)• Donald Unwin - England• Carlo Croce - Italy • Aldo Bullo – Italy (2003)

Did any work ofde Dondi’s family survived?

• In 2003 Mr. Aldo Bullo discovered in the Tower of S. Andrea in Chioggia a medieval clock.

• Documents in the Chioggia Archives certify that the clock existed at least since February 26th 1386.

• Was this clock from Dondi’s workshop?

Papers published• Addomine, M., Bullo, A., Pennestrì, E.,

La scoperta a Chioggia di un orologio da torre del 1386, La Voce di Hora, n.21, Dicembre 2006 pp. 5 – 19

• Pennestrì, E., Pezzuti, E., Valentini, P.P., Vita, L., Computer-aided reconstruction of Italian ancient clocks , Computer Animation and Virtual Worlds, Wiley Interscience, vol.17, 2006, pp.565-572.

Virtual reconstruction ofclockwork at

University of Rome Tor Vergata

• At University of Tor Vergata one line of research is the kinematic structure analysis of ancient clockwork.

• Many students with their theses contributed to the virtual reconstruction of ancient clocks

The waterclock of al Jazari

The astrarium of Richard of Wallingford

The Fanzago’s clock (Clusone)

The Fanzago’s clock (Clusone)

The Fanzago’s clock (Clusone)

Piazza della Loggia Clock (Brescia)

Piazza della Loggia Clock (Brescia)

Piazza S. Marco (Venezia)

Piazza S. Marco (Venezia)

Clock of Michele Canonico

Clock of Michelangelo Canonico

Clock of Michele Canonico

Conclusions

• It has been presented an overview of the life and works of the Jacopo and Giovanni Dondi.

• Mechanical engineers should be involved in History of Science and, more particularly, in ancient clock analysis.