Snapshots on the works and life of Giovanni Dondi Distinguished Italian Clockmaker

1. Snapshots on the works and life ofGiovanni Dondi Distinguished Italian Clockmaker Prof. Ettore Pennestrì Università di Roma Tor Vergata December 2008 Seminar for the visiting Students of the Board of European Students of Technology

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

3. 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

4. Chioggia, Padova, Venezia

5. 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

6. Jacopo Dondi’s astronomical clock

7. 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.

8. 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.

9. 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.

10. 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.

11. 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.)

12. 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.

13. 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.

14. The Ptolemaic model

15. The Ptolemaic cosmological model

16. How Giovanni Dondi mechanically reproduced this motion in his Astrarium?

17. 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

18. 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.

19. Adsit Initio Deus Medium Comitetur Et Opus Propositum Ducat in Finem Tractatus Astrarii Johannis De Dondis Paduani Civis Cui Tres Sunt Partes

20. 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).

23. Astrarium • The astrarium stood about 1 m high • Consisted of a seven-sided brass or iron framework resting on 7 decorative paw-shaped feet.

24. 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.

25. 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.

26. The seven dials

27. 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.

29. 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.

30. The foliot verge escapement

31. 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.

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

34. Primummobile

36. 24 h = 86400 s

37. 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. .

38. Jupiter

39. Mars

40. Moon

41. Mercury

42. Saturn

43. Venus

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

47. 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.

48. 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.

49. 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.

50. 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.