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Astronomical clock, c. 1762–1769 David a. S. Cajetano (Rutschmann), Vienna
Case: wooden case with glazing on all four sides Height: 265 cm, width: 77 cm, depth: 49 cm Dial and indicators: silvered brass dials with engraving and cast decorations, steel and gilt-brass hands, signed and dated on the front dial: “Fr. David a. S. Cajetano – Augustini Discalc Invenit et Fecit, Viennae”, “1769”. Auxiliary dials on the main front face, starting with the bottom dial and proceeding clockwise: (1) time of day with hour and minute hands; (2) sidereal position of the planet Mercury (period of rotation: 87 days, 23 hours, 14 minutes and 4 seconds); (3) day of the week; (4) sidereal motion of the moon with indication of days it takes the moon to reach a lunar node; (5) sidereal position of Jupiter (period of rotation: 11 years, 314 days, 22 hours); (6) epacts, indiction and golden number; (7) sidereal position of Saturn (period of rotation: 29 years, 167 days and 22 hours); additionally, a double-ended hand indicates the precession of the equinoxes, i.e. the variation in the position of the earth’s rotational axis that causes the shift of the equinoctial points; duration of a full revolution of this hand: 20,904 years; (8) dominical letter and solar cycle; (9) sidereal position of Mars (period of rotation: 1 year, 321 days, 23 hours, 31 minutes and 56 seconds); (10) synodic period of the moon, i.e. age of the moon (29 days, 12 hours, 44 minutes); (11) moon 44
anomaly, i.e. angular distance of the moon from its apogee; period of rotation: 27 days, 13 hours, 16 minutes and 35 seconds; (12) sidereal position of Venus (period of rotation: 224 days, 16 hours, 48 minutes). Upper front dials: “Bohemian” or “Italian hours”; the dragon hand, sun hand and moon discs indicate the times of solar and lunar eclipses. Two round apertures on the sides, one showing the size of a lunar eclipse and the other a blue and golden sphere that indicates the lunar phase. Main dial ring: days, months, signs of the zodiac, lunar nodes, full moon and new moon; a doubleended hand with the inscribed letters “A” and “P” indicates the apogee and perigee of the moon, and a combination of central and peripheral numerals permits readings of the accurate time in 83 different places, according to their respective geographical longitude. Four small circular apertures show the current year, up to 9999. Rear face: perpetual calendar, hour, minute and, indicated by a gilded minute hand, the true solar time for Vienna. Movement: brass and steel going train, weight-driven movement with a 26 kg lead weight, Graham escapement, seconds pendulum, duration approx. 32 days. Inv. no. U 435 Purchased from Zwettl Abbey, 1928
The whole universe, enclosed in a clock. And indeed, the seemingly innumerable wheels which interconnect in the gear trains of the “Cajetano clock” – some 150 in all, says one who has held each of them in his hands – reflect our concept of the cosmos: an intricate clockwork that keeps turning and moving, following an inexplicable momentum. From the very first beginnings of clockmaking, astronomy affected the development of the clockmakers’ profession. And vice versa, it was the mechanics of clocks which soon came to determine our ideas about the heavens and what is going on there. The makers of astronomical instruments were among the earliest members of the new craft in the 14th century, and not a few of them pursued their research in monasteries. One of those whom a religious order gave an opportunity for higher learning was David Rutschmann (1726–1796), the son of a carpenter from the Black Forest. A joiner by profession, Rutschmann entered the Order of the Discalced Augustinians in 1754 and henceforth called himself Frater David a Sancto Cajetano. He proceeded to study mathematics, mechanics and astronomy in Vienna and applied his insights to the work on his astronomical clock, which was destined for his monastery in Vienna. On March 21, 1769 he handed over his amazing creation to his abbot. Cajetano had succeeded in building an incomparably complex and precious machine, and he left posterity to marvel at how he translated brilliant astronomical understanding at the highest level of his time into an amazing work of outstanding craftsmanship.