Complete text (abstract only):
Zach and the Prussian officer Friedrich Carl Ferdinand von Müffling (1775-1851) started a survey in 1803. The first campaign had the target to obtain a net of exactly known geographical places. The latitudes of these places were fixed with solar observations and by the registration of upper and lower culminations of stars. The differences in longitudes between these places and the Seeberg observatory (as exactly known reference point of the survey) were determined with a »transport« of local time by powder lightnings. These signals were sent from the mountains Inselsberg, Schneekopf, Hörselberg and Brocken (Harz) especially.
We have checked the longitudes measured with the help of powder lightnings. For that purpose we took only such geographical places (in the System 40, Bessel Ellipsoid) into account that agree with Zach's descriptions. The mountain tops in Thuringia are relatively flat. Already for that reason errors of the order of some arcseconds could appear in the comparison between Zach's values and its coordinates in the System 40 (at 51 latitude 1" 20 m).
The differences between Zach's and the modern longitudes are given in Table 1. The longitude of the Geba mountain is rather inexact. The other values have errors of the order of 2 seconds of time for the more distant stations (Dietrichsberg, Wartburg, Ettersberg,) and of the order of 1 second of time for stations near the observatory at Seeberg. Zach himself supposed the error of time to be of the order of one second.
References
Zach, F. X. von: Nachrichten von der Aufnahme von Thüringen und dem Eichsfelde, Gotha 1806
Tab. 1 Deviation of the longitudes of Zach's campaign from System 40
| Place | Deviation in arcsec (east/west) |
| Dietrichsberg | 36.38 e |
| Gebaberg | 104.68 e |
| Wartburg | 31.36 e |
| Inselsberg | 23.77 e |
| castle Friedenstein, eastern tower | 11.64 w |
| Schneekopf | 8.62 w |
| Ettersberg | 33.01 w |
Bibliographical details:
Oliver Schwarz, Wolfgang Conrad: Differential longitudes in Thuringia. In: Peter Brosche, Wolfgang R. Dick, Oliver Schwarz, Roland Wielen (Eds.): The Message of the Angles - Astrometry from 1798 to 1998. Proceedings of the International Spring Meeting of the Astronomische Gesellschaft, Gotha, May 11-15, 1998. (Acta Historica Astronomiae ; 3). Thun ; Frankfurt am Main : Deutsch, 1998, p. 92-93.
Html-Version: Wolfgang R. Dick. Created: 21 Jan 1999