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Research Coins: Feature Auction

Sale: CNG 61, Lot: 2747. Estimate $1500. 
Closing Date: Wednesday, 25 September 2002. 
Sold For $1200. This amount does not include the buyer’s fee.

ROMAN. 2nd-3rd century AD. Bronze circular portable sundial (horologium, solarium). Æ 93 gm. 55 mm. Voided semicircular arc attached to protractor-shaped dial with twelve hour segments divided by shallow lead inlaid grooves radiating from central hub, within which are the remains of gnomon base. For a portable sundial in Oxford Museum of History and Science, see O. Dilke, Mathematics and Measure, Reading the Past, British Museum Publications, 1993, fig. 41. For general reading and a comprehensive catalogue of sundials, see S. Gibbs, Greek and Roman Sundials, Yale University Press, 1975, especially figs. 58-59. Well preserved with green patina. ($1500)

Sundials or shadow clocks in one form or another have been used by different societies for more than 5000 years. Herodotus (2. 109.3) in the 5th century BC stated that ‘knowledge of the polos (sundial) and the gnomon (shadow stick) and the twelve divisions of the day came into Greece from Babylonia’. The first device for indicating time, dating from about 3500 BC, was probably a simple gnomon, a vertical shadow-stick or pillar, the length of which cast a shadow indicating the time of day. The Chaldaeans and Sumerians also seem to have been the first to have divided the week into seven days, the year into twelve months and the sky into the twelve signs of the zodiac. Sometime between 1800-1200 BC the Egyptians had developed an astronomical calculating system called the decans which also provided the basis for the division of the day in 24 hours. By the 8th century BC more precise devices were in use; the earliest known sundial still preserved is an Egyptian shadow-clock of green basalt from this period. [new paragraph] In the 4th century AD the Greek author, Diogenes of Laerte, quoting the philosopher Favorinus (2nd century AD), credits Anaximander of Miletos with inventing the gnomon and setting it up at Sparta in about 580 BC. In about 340 BC Berosus, a Chaldaean astronomer-priest living in Egypt, developed the hemisphericum in which the gnomon was placed in a hollowed out hemisphere. From this Apollonius of Perge in about 250 BC, developed the hemycyclium. In the first century BC the celebrated Tower of the Winds was erected in Athens, primarily to house a klepsydra (‘waterclock’), and is known to have had a large sundial carved into each of its octagonal walls. [new paragraph] By the Roman period there was a great variety of sundial types in use. The first clock known to have been set up in Rome was the sundial captured by the consul Valerius Messalla at Catania during the First Punic War in 264/3 BC, but it was not until 99 years later, in 164 BC, that it was correctly set. The architect and engineer Marcus Vitruvius Pollio in book 9 of De architectura, written in AD 27 and only rediscovered in 1486, gives the most complete description on dials in an ancient source. Vitruvius lists 13 kinds of sundials, including portable ones used in surveying, for calculating due south by the position of the sun at midday. Vitruvius also describes the celebrated sundial built by Augustus in 10/9 BC which covered a vast area in the campus Martius near the Ara Pacis and had a 7th century BC Egyptian obelisk of Psamtik II from Heliopolis, now in piazza Montecitorio, as its vertical gnomon. Besides being emperor, Augustus in his capacity as Pontifex Maximus also had responsibility for keeping the civil calendar in step with the seasons, which at this date meant fine-tuning Caesar’s system. This monumental sundial combined time-keeping, religious, political and ideological functions. The ideological function was not lost on Cicero when Caesar first introduced his calendar: ‘the heavens have to obey the dictator’, Plutarch Caesar 59. [new paragraph] Vitruvius clearly specified in chapter 7.7 the kind of time a dial would show the viewer: ‘In all figures and diagrams the effect will be the same, that is to say, the equinoctial as well as the solstitial days, will always be divided into twelve equal parts’. Each arc was divided in into twelve equal divisions, and each ray, reckoned from sunrise to sunset, had, therefore, 12 equal intervals or hours. Because the length of the day varied according to the season, these hours likewise varied and were consequently known as temporary hours, which were widely used throughout the civilized world until the advent of the mechanical clock in the 14th century. [new paragraph] In AD 150 Ptolemy of Alexandria summed up the astronomical knowledge of the age in Mathematike syntaxis, including how to draw the hour lines of a sundial and setting forward his famous theory that the earth was at the centre of the universe in sharp contradiction to Aristarchus of Samos, who had hypothesed in the 4th century BC that the earth revolves around the sun and that it rotates on its own axis. This work was fortunate to survive the tragic burning of the great library of Alexanderia in the 7th century, translated in the 9th century into Arabic and became know as Almagest, a compound of the Arabic article and the Greek adjective megiste, ‘the Greatest’. Ptolemy’s theories, as transmitted by the Arabs, were accepted by the scientific world until the time of Copernicus and Kepler in the sixteenth century