Astrarium of Giovanni Dondi dell'Orologio

The Astrarium of Giovanni Dondi dall'Orologio was a complex astronomical clock built between 1348 and 1364 in Padua, the capital of an independent Signoria, by the doctor and clock-maker Giovanni Dondi dall'Orologio. The Astrarium had seven faces and 107 moving parts; it showed the positions of the Sun, the Moon and the five planets then known, as well as religious feast days. It was one of the first mechanical clocks to be built in Europe.

Dondi documented the Astrarium in detail in the Tractatus astrarii, which is the earliest complete surviving description of its kind; the St Albans abbey clock designed by Richard of Wallingford predates it, but survives only as fragments (reconstructed by John North). 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.

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". 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. 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.) The astrarium stood about 1 metre high, and consisted of a seven-sided brass or iron framework resting on seven 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 seven dials, each about 30 cm in diameter, showing the positional data for the Primum Mobile, Venus, Mercury, the Moon, Saturn, Jupiter, and Mars. 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, 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, 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 ta

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