II. - Schloss Schwetzingen

II.
74
II. Schwetzingen – A Prince Elector’s Eighteenth-Century Summer Residence
although it was intersected by the railway in
later years.
Later writers have confi rmed Mayer’s precise
survey, more precise than that undertaken by
Cassini de Thury. 28 Mayer found the distance
to be 6.238,72 toises (toise du Perou), approximately
12,16km. On this baseline from Ketsch
to Rohrbach, Mayer aligned his triangular net.
The merits of triangulation were that only
one baseline had to be precisely measured;
the remaining sides of the triangle could be
determined mathematically. Mayer published
his fi ndings in 1763, in a tract printed at
Mannheim, Basis Palatina 1762, ad normam
academiae Regiae Parisinae scientaiarum
exactam bis dimensa, anno 1763, novis
mensuris aucta et confi rmata, recentissimisque
observationibus et calculis stabilata. Ten
years later he published his map of the region
surveyed between Heidelberg, Mannheim
and Schwetzingen, the small Charta Palatina
drawn to a scale of 1:75000. It covered an area
of 360 km 2 .
Geographical Position of the Schwetzingen
Observatory
Measurements taken during the lunar eclipse
of 17th March 1764, and the eclipses
28 Andreas Weiss, “Die Charta Palatina des Christian Mayer”
in: Mitteilungen des Historischen Vereins der Pfalz, vol.
26, Speyer 1903, pp. 1-40., Hans Schmidt, “Der Urmassstab
Christian Mayers” in: Mannheimer Hefte, No.1, 1976 pp.
14- 18, Heinrich Merkel, Die geodätischen Arbeiten Christian
Mayers in der Kurpfalz, Karlsruhe 1928, “Kartographie und
Vermessungswesen” in: Kistner, 1930, pp. 48-56.
of Jupiter’s moons in 1765 and 1766, allowed
Mayer to determine the exact longitude of the
Schwetzingen observatory (26° 18” 30’). To
determine its latitude, Mayer measured a total
of 76 meridian heights between 1765 and
1766, calculated the mean and gave the value
as 49° 23” 4,5’.
Finally, he determined the Schwetzingen
meridian that was needed for the aligning of
the planned survey. For this Mayer used the
azimuth method.
In 18th-century Germany only eight places
had been precisely located by astronomical
means, and Mayer’s work was widely applauded.
29 Experts noted with satisfaction
that Schwetzingen now had its place among
those select few, that the relevant fi ndings
would be included in the yearbooks of foreign
academies, that the scientist himself would
be honoured by the membership of those
academies. 30
Suddenly, Schwetzingen had a place in the
coordinate system of the Earth’s survey. To the
Elector it must have been a pleasant thought
that at least as far as astronomical positioning
was concerned, his summer residence had
now caught up with Paris and London.
(Kai Budde)
29 Kistner, 1930,pp. 53.
30 GLA 213/3540 Acta die neue Sternwarte zu Mannheim betreff.
Vol. I., Denkschrift Chr. Mayers vom 31. 12. 1771, p. 2.