Would you like to have as a friend a person who, having inherited from his father a considerable love of studies, becomes one of the greatest experts in astronomy, philosophy and medicine? Who is highly esteemed by the most talented scholars in Italy, Germany and Hungary?
Who is appointed personal physician to Charles IV of Bohemia, who teaches medicine and astronomy in Padua, medicine in Florence and then again in Padua and who, despite these commitments, is also a great traveller, mainly to teach but also to treat powerful people and to be a negotiator on behalf of the municipality of Padua?
A scholar, an erudite man who carried out important studies on the plague, like his father before him on thermal waters (he was the first to have one of the first ‘establishments’ built in Abano) and, finally, he carried out studies on Roman obelisks.
If I could have, I would have loved to have known him and had him as a friend, if that term could have been used in the mid-1300s. To know and esteem him just as Francesco Petrarch did, who held him in such high esteem and great friendship that he dedicated a few verses to him and bequeathed him 50 gold ducats, despite the fact that the great poet hated doctors.
Giovanni Dondi was born in Chioggia in 1318, the son of Jacopo, a doctor, philosopher and astronomer. His father was a man of many interests and with a marked practical sense. He was one of the first builders of an astronomical clock that was placed on the tower of the Palazzo dei Signori in Padua. This achievement made such an impression on his contemporaries that he was able to add “dell’orologio” to his surname and that of his descendants.
John was born in this context, but his work cannot be understood without placing him correctly in his family, but above all in his time. At that time, the stars were consulted for all important decisions, for waging war or postponing it. Doctors thought that they had an influence on the “humours” and on almost the whole life of individuals. The exact knowledge of the position and virtues of the celestial bodies allowed a correct diagnosis and an “appropriate” treatment. One did not become a doctor without being a good astrologer.
That is why first Jacopo and then Giovanni had to study astrology, astronomy, arithmetic, geometry and music at university. Today this seems very strange to us, but at the time this was the way.
This also explains how a scholar with a great passion for technology and a great practical sense could build a clock, or rather a complex astronomical instrument.
The clock of celestial movements, the planetarium built by Dondi is better known as the Astrarium, a very complicated machine, then as now, that encompassed all the astronomical knowledge of the time. It took about sixteen years of study, design, work, mistakes and remakes.
To make it (no doubt helped by his father and a certain Antonio who had already worked with him), he had to face and solve many mechanical obstacles, for example to compensate for the elliptical orbits of the Moon and Mercury he had to build elliptical gears. He had to study and remedy the irregular orbit of Venus.
Giovanni Dondi’s astrarium, reconstructed by Guido Dresti di Craveggia, can be seen in the Time Room of the Poldi Pezzoli Museum in Milan, Via Alessandro Manzoni 12.
First documented example of wheels with teeth on the inside and wheels with helical teeth. Documented because our Giovanni left us the description and drawings of every part of his Astrarium, how to assemble them and how to correct any errors. What he left us is also one of the earliest known treatises. A text that has allowed the reconstruction of this wonderful instrument today because the original has been lost.
It is a single instrument but divided into two parts. The upper, larger part consists of seven quadrants showing the trajectories and positions of the Sun and Moon, the orbits and positions of Venus, Mars, Jupiter, Saturn and Mercury according to Aristotelian/Tolemaic theory.
The lower part housed the movement and showed the mean hours and minutes from ten to ten, the first known example in which they appear. On a large disc are engraved the days of the year, divided by months and for each day the corresponding saint and the religious holidays, fixed and mobile. Sunrise and sunset referred to Padua, sidereal time.
The whole thing is driven by a single weight and a verge escapement with a ring balance and not by a simple folliot. A very complex machine with around two thousand components. In the accurate but essential reconstructions that can be seen today, the decorations that must have been there and the protection of the lower part that served to hide and protect the movement do not appear.
Some sources give Giovanni Dondi as dead in Genoa in 1389, but more recent information says that he died in Abbiategrasso and that he was briefly buried in San Eustorgio and only later transported to Padua.
Yes, I would have loved to have been friends with Giovanni Dondi dell’Orologio.