Giovanni Dondi dell'Orologio

Giovanni Dondi dell'Orologio
Born	Giovanni de' Dondi 1330 Chioggia
Died	19 October 1388 Abbiategrasso
Occupation	doctor, clock-maker
Known for	The Astrarium

Giovanni Dondi dell'Orologio (1330–1388), also known as Giovanni de' Dondi, was a doctor and clock-maker in Padua, Italy. He is remembered today as a pioneer in the art of clock design and construction. The Astrarium, which he designed and built over a period of 16 years, was a highly complex astronomical clock and planetarium, constructed only 60 or so years after the very first mechanical clocks had been built in Europe, and demonstrated an ambitious attempt to describe and model the solar system with mathematical precision and technological sophistication.

Giovanni de' Dondi's Astrarium. Tracing of an illustration originally from his 1364 clock treatise, Il Tractatus Astarii. It doesn't show the complex upper section with its many wheels, but just the weights, escapement, and main gear train.

Life

Giovanni was the second son of Jacopo Dondi dell'Orologio and Zaccarota Centrago or Centraco of Chioggia. His father was a doctor and astronomer, and builder of a large astronomical in the tower of the Palazzo Capetanato of Padua in 1344.

Giovanni lived with his father from 1348 to 1359, and shared his father's interest in astronomy and clockmaking. In 1348 he began working on what he called his astrarium or planetarium. He described in detail the design and construction of this project, which was to occupy him until 1364. His manuscripts provided enough material for modern clockmakers to build reconstructions. In 1371 he served as ambassador to Venice, but after the conflict between Padua and Venice in 1372, joined the University of Pavia, and served as diplomat and scholar until his death in Abbiategrasso on 19 October 1388. He is buried at Sant'Eustorgio in Milan.

Giovanni Dondi and the Padovana chicken

It is frequently reported, in sources from the 19th and early 20th centuries to the present, that the "Marquis Giovanni Dondi dell'Orologio" was responsible for introducing the Padovana chicken, which closely resembles the Polish breed, from Poland to Italy. However the Dondi who was ennobled was the soldier Francesco Dondi, created Marquis by King John III Sobieski in 1676; no journey to or contact with Poland by Giovanni Dondi in the 14th century is documented.

Written works

Dondi wrote on a wide range of subjects. His most celebrated work is the Tractatus astrarii or Planetarium, which describes the Astrarium. It is the earliest surviving description of its kind; the Albion of Richard of Wallingford predates it, but is lost. In the introduction, Dondi writes that his machine was built in accordance with the 13th-century Theorica planetarum of Campano di Novara, and to demonstrate the validity of the descriptions of the motion of heavenly bodies of Aristotle and Avicenna. The Tractatus survives in twelve manuscript sources. The autograph in the Biblioteca Capitolare of Padua (MS. D39) and a copy of it, also in Padua, are certainly the work of Dondi. The other sources are rewritten versions of the autograph, to which Dondi's contribution is as yet unclear. The autograph manuscript was published in 1987 in a critical edition with colour facsimile and French translation by Poulle as the first volume of the Opera omnia of Jacopo and Giovanni Dondi.

Of the twenty-nine lectures on medical topics, the Sermones and Colationes, delivered between 1356 and 1388, only the titles survive, with the exception of one, the Sermo in conventu magistri Iohannis ab Aquila in medicina 1367 (Bibliothèque Nationale, Paris, Lat. 9637), and some passages from that in Bologna in the same year cited by Francesco Scipione Dondi dall'Orologio.

The twenty-four Quaestiones super libris Tegni, dating from about 1356, are preserved in a manuscript begun in 1370 by Tommaso da Crema and now in the Biblioteca Palatina of Parma (Parmense 1065); Tegne was the mediaeval name for the summary by Galenus of the works of Hippocrates. The Quaestiones are to date unpublished, as are Dondi's Experimenta or medical prescriptions, conserved in a manuscript of Iohannes de Livonia dated 1453 and now in the Biblioteca Civica of Padua (C.M. 172).

Another lost work, a tractatulum Galieni occultam seriem explicantem in distinctione dispositionum corporum humanorum, quorum in libro Microtegni sub brevitate restrinxit reales differentias inter illas, preterquani in paucis assignatum, was probably written at Pavia during the plague of 1383, and may have discussed the De complexionibus of Galenus.

The short practical treatise on the avoidance of plague, De modo vivendi tempore pestilentiali, was written shortly afterwards; it was published, in Italian, by Zambrini in 1866,and by Sudhoff in 1911.

In natural science, Dondi wrote De fontibus calidis agri Patavini, dedicated to his friend Iacopino da Angarano, and preserved in autograph manuscript in the Biblioteca del Seminario of Padua (ms. 358) and in a copy in the Biblioteca Ambrosiana in Milan (H 107 sup.). Together with the Tractatus de causa salsedinis aquarum et modo conficiendi sal artificiale ex aquis Thermalibus Euganeis by his father Jacopo, it was published by Tommaso Giunti in De balneis omnia quae extant apud Graecos, Latinos et Arabas in 1553.

A manuscript in the Biblioteca Nazionale Marciana (Ms. lat. XIV 223 (4340)), though not in Dondi's hand, contains both his own literary work and selections copied from that of others. It contains his Iter Romanum, which describes the Roman monuments of Rimini and Rome in a scientific manner, with measurements and transcriptions of inscriptions, and was published by Rossi in 1888; his Epistolario of twenty-eight letters, of which the two to Petrarch have attracted particular attention; and his Rime, consisting of forty-two sonnets, five madrigals and three ballate, published by Medin in 1895 and Daniele in 1990.

Dondi's quaedani apostillae or notes on a letter of Seneca, mentioned in a manuscript of Gasparino Barzizza from 1411, have not been traced.

The Astrarium

The astrarium was considered to be a marvel of its day. Giovanni Manzini of Pavia writes (in 1388) that it is a work "full of artifice, worked on and perfected by your hands and carved with a skill never attained by the expert hand of any craftsman. I conclude that there was never invented an artifice so excellent and marvelous and of such genius".

de' Dondi writes that he obtained the idea of an astrarium from the Theorica Planetarum of Giovanni Campano da Novara, who describes the construction of the equatorium.

The astrarium was primarily a clockwork equatorium with astrolabe and calendar dials, and indicators for the sun, moon, and planets. It provided a continuous display of the major elements of the solar system and of the legal, religious, and civil calendars of the day. de' Dondi's intention was that it would help people's understanding of astronomical and astrological concepts. (Astrology was then considered a subject worthy of study by the intellectual elite and was taken reasonably seriously.)

Description

The astrarium stood about 1 metre high, and consisted of a seven-sided brass or iron framework resting on 7 decorative paw-shaped feet. The lower section provided a 24 hour dial and a large calendar drum, showing the fixed feasts of the church, the movable feasts, and the position in the zodiac of the moon's ascending node. The upper section contained 7 dials, each about 30 cm in diameter, showing the positional data for the Primum Mobile, Venus, Mercury, the moon, Saturn, Jupiter, and Mars.

de' Dondi constructed the clock, with its 107 gear wheels and pinions, entirely 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. In some cases, de' Dondi used near-elliptical wheels, in order to more accurately model the irregular motions of the planets (using the Ptolemaic epicycles rather than the ellipses as later worked out by Johannes Kepler). On some of these wheels, the teeth varied in size and spacing along the wheel's periphery. To indicate dimensions in his descriptions, de' Dondi used units such as the width of a goose quill, the thickness of a blade of a knife, or the breadth of a man's thumb.

For data on the motion of the planets, he consulted the Alfonsine tables, compiled in about 1272.

The clock movement

The clock movement had a balance wheel regulated to beat at the rate of 2 seconds. Its simple wheel train turned a dial marked on the margin with a scale of 24 equal hours and 10 minute intervals. The dial rotated anticlockwise against a fixed pointer, showing mean time, and could be adjusted if necessary by intervals of 10 minutes of time by sliding out a pinion of 12 teeth that meshed with the 144 teeth of the main dial. On each side of the clock dial was a fixed plate or 'tabula orientii', graduated with months and days of the Julian calendar for the purpose of determining the times of the rising and setting of the mean sun for the latitude of Padua (about 45°deg N). At the time the clock was made, the dates of the solstices were 13 June and 13 December (Old style or Julian Calendar).

The calendar wheel

The annual calendar wheel or drum in the lower section was about 40 cm across. This drove the calendar of movable feasts, and the dials above. Around the outside of the wheel was a broad band divided into 365 strips, each containing numbers that indicated the length of daylight, the dominical letter, the name of the saint for that day, and the day of the month. Alternate months were gilded and silvered, and the engraved letters filled alternately with red and blue enamel. de' Dondi didn't introduce any indications or allowances for leap year - he recommended stopping the clock for the entire day.

The Primum Mobile dial

Directly above the 24 hour dial is the dial of the Primum Mobile, so called because it reproduces the diurnal motion of the stars and the annual motion of the sun against the background of stars. It is basically an astrolabe drawn using a south polar projection, with a fixed tablet and a rete of special design that rotated once in a sidereal day. The rete was provided with 365 teeth, but was driven by a wheel with 61 teeth which made 6 turns in 24 hours. Thus the rete rotated once in 365/366 of a mean solar day, which equated 366 successive meridian transits of the vernal equinox with 365 similar transits of the sun. de' Dondi realised that his approximations didn't correspond with the exact length of the solar year, and recommended stopping the clock occasionally so that it could be adjusted.

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. For example, de' Dondi's dial for Mercury uses a number of intermediate wheels, including: a wheel with 146 teeth, two oval wheels with 24 irregularly shaped teeth that meshed together, a wheel with 63 internal (facing inwards) teeth that meshed with a 20 tooth pinion. The 63-tooth wheel made one rotation a year, non-uniformly because of the oval driving wheels, and made the main indicator wheel rotate through 63/20 × 12 signs of the zodiac each year. This is equivalent to 37 signs and 24°, a good approximation to the value of 37 signs and 24° 43' 23" required by theory.

What happened to the clock?

In 1381 de' Dondi presented his clock to the Duke Gian Galeazzo Visconti, who installed it in the library of his castle in Pavia. It remained there until at least 1485. It may have been seen and drawn by Leonardo da Vinci. The clock's final fate is unknown.

Modern reconstructions

Because de' Dondi described most of the more complex components of his clock in his manuscripts in considerable detail, it has been possible for modern clockmakers to build convincing - if sometimes speculative - reconstructions. Seven of such reconstructions were built by Peter Haward of Thwaites and Reed, London; examples of these can be found in the Smithsonian Institution and The Time Museum Illinois. There is also a reconstruction unit in the Musee International d'Horologerie in La Chaux-de-Fonds, Switzerland, with Luigi Pippa signature on frame.

Further reading

• Bedini and Madison, 1966 "Mechanical Universe : the Astrarium of Giovanni de' Dondi" (Transactions of American Philosophical Society)
• King, Henry "Geared to the Stars: the evolution of planetariums, orreries, and astronomical clocks", University of Toronto Press, 1978
• Baillie G. H., Lloyd H. A. and Ward F. A. B., "The Planetarium of Giovanni de Dondi citizen of Padua", 1974 London
• Catherine Cardinal, Jean-Michel Piguet, 2002, "Catalogue of Selected Pieces", ISBN 2-940088-10-1

External links

• a replica built by Italian clockmaker Carlo G Groce [1]