Die weltweit erste Messung einer Lotabweichung in der L\"ange

TL;DR

In 1837, Christian Ludwig Gerling conducted the first global measurement of a vertical deflection in longitude by comparing astronomical and geodetic data, confirming modern vertical deflection values.

Contribution

This paper documents the pioneering 1837 measurement of vertical deflection in longitude, a significant historical achievement in geodesy and astronomy.

Findings

Results agree with modern vertical deflection data

First successful measurement of longitude deflection

Validated the consistency of astronomical and geodetic methods

Abstract

During the summer of 1837 Christian Ludwig Gerling, a former student of Carl Friedrich Gauss, organized the world wide first determination of a vertical deflection in longitude. From a mobile observatory at the Frauenberg close to Marburg (Hessen) he measured the astronomical longitude difference between the observatory of C.F. Gauss at G\"ottingen and the observatory of F.G.B. Nicolai at Mannheim. By comparing these astronomical results with the geodetic determined longitude differences, which he just had measured as a part of the triangulation of Kurhessen, he was able to extract a combined value of the vertical deflection of G\"ottingen and Mannheim. His results are in very good agreement with modern vertical deflection data.