Ear sundial by Philipp Matthäus Hahn
The Öhrsonnenuhr of Philip Matthew Hahn is a sundial with the sighting device , which is to be rotated by the user so against the sun, that the (one of a pinhole eye as grain or as nodus light spot) generated on a marker (the rear sight , or the single line on the dial). The rotation of the visor (around the polar axis ) is transferred to an hour and a minute hand with cogwheels, which indicate the time of day on a round 12-hour / 60-minute dial . Hahn used this sundial without a magnetic needle to align the clocks that he also built .
history
Hahn built the first eye sundial in 1763. After that, a large number of this type of sundial came into being, many of which come from his sons and his employees whom he employed in his workshops. Eye sundials were included for testing his grandfather and pocket wheel watches.
In general, the portable “Augsburg Equatorial Sundial” (mostly made in Augsburg between 1700 and 1800 ) can be used as a model. In particular, it is the minute sundials . These are specimens with toothed wheels with which the setting movement is transferred to a minute hand.
The minute sundials were only used to determine the true local time and were equipped with a polos ( pole rod ) as a shadow thrower. Hahn designed his sundial to display the mean local time , for which a nodus is necessary. A perforated screen ( eye ) offered itself as such . The light spot created in this way can be read more precisely than the shadow point of a small disk or sphere. The prerequisite is that the aperture is always positioned towards the sun, which happens anyway when you aim for the sun before reading. The name of the eye sundial chosen later helps to distinguish the Hahn watch type from its close predecessors.
function
The Hahn'sche Öhrsonnenuhr and the adjustable “Augsburg Equatorial Sundial” are special forms of a sundial. Their specialty is that the user has to make a setting and only then can read off the time of day: passive sundials .
With Hahn's eye sundial , a four-sided frame that can be rotated around the polar axis (parallel to the earth's axis ) is set when aiming. The side with the pinhole and the opposite side with the marking are parallel to the polar axis. The lower part of the frame is parallel to the equator and carries the dial with hour and minute scale. The frame is turned towards the sun. Like the sun, it rotates linearly around the polar axis (15 ° per hour). The translation with the gear train - especially on the minute hand - acts as a "mechanical magnifying glass" and increases the display accuracy.
The sundials usually had an analemma loop scaled with calendar data as a marker for reading the mean local time . The aperture often had a second hole and the image area had an additional straight mark so that the true local time could also be determined. Both holes were offset laterally from the center, which made a continuous axis possible.
The Hahn'sche Öhrsonnenuhr is a portable sundial. The latitude at the place of use must be known in order to adjust the inclination of the polar axis appropriately. The clock must be set up so that the polar axis is in the meridian plane . Hahn did without the usual addition of a compass to his watch. The notes on usage ... enclosed with each copy show that the installation was carried out with the aid of the advertisement itself. That took at least a whole day, because the proof of the correct arrangement has only been provided ... if the sun points stay all day ... on the present day of the month and do not move higher and lower .
This procedure was repeated with each new installation. Only the inclination of the polar axis was retained because the meridian ring carrying it was suspended from a bracket. Versions on a levelable base plate were rarer.
literature
- Max Engelmann: Life and work of the Württemberg pastor and precision engineer Philipp Matthäus Hahn , Richard Carl Schmidt & Co., Berlin 1923
- Ernst Zinner: German and Dutch Astronomical Instruments from the 11th to 18th Centuries , Becks'che Verlagsbuchhandlung, 1956
- Philipp Matthäus Hahn 1739–1790, exhibitions of the Württembergisches Landesmuseum Stuttgart and the cities of Ostfildern, Albstadt, Kornwestheim, Leinfelden-Echterdingen , Stuttgart 1989, 2 volumes
Individual evidence
- ^ A b Max Engelmann: Life and work of the Württemberg pastor and precision engineer Philipp Matthäus Hahn , Richard Carl Schmidt & Co., Berlin 1923, p. 128
- ↑ Ernst Zinner: German and Dutch astronomical instruments from the 11th to 18th centuries , Becks'che Verlagsbuchhandlung, 1956, p. 91
- ↑ Wolfgang Eckhardt: Claude Dunod, Michael Bergauer and Johann Willebrand - on the history of the minute sundial , clocks - old and modern time measurement, October 1987, pp. 30–48, illustrations of 7 minute sundials
- ^ Arnold Zenkert: Faszination Sonnenuhr , Verlag Harry Deutsch, 2005, images of two minute sundials on p. 22 and 31
- ↑ Wolfgang Eckhardt: Claude Dunod, Michael Bergauer and Johann Willebrand - on the history of the minute sundial , clocks - old and modern time measurement, October / 1987, p. 31
- ^ For example by Max Engelmann: Life and work of the Württemberg pastor and precision engineer Philipp Matthäus Hahn , Richard Carl Schmidt & Co., Berlin 1923, p. 130
- ^ Max Engelmann: Life and work of the Württemberg pastor and precision engineer Philipp Matthäus Hahn , Richard Carl Schmidt & Co., Berlin 1923, pp. 213–215 (appendix)
- ↑ Max Engelmann: Life and work of the Württemberg pastor and precision engineer Philipp Matthäus Hahn , Richard Carl Schmidt & Co., Berlin 1923, p. 214 (appendix)
- ^ Philipp Matthäus Hahn 1739–1790, exhibitions of the Württembergisches Landesmuseum Stuttgart and the cities of Ostfildern, Albstadt, Kornwestheim, Leinfelden-Echterdingen , Stuttgart 1989, Part 1: Catalog, 8 copies on pp. 368–373
- ^ Philipp Matthäus Hahn 1739–1790, exhibitions of the Württembergisches Landesmuseum Stuttgart and the cities of Ostfildern, Albstadt, Kornwestheim, Leinfelden-Echterdingen , Stuttgart 1989, part 1: Catalog, 1 copy on p. 370