Ann. Geophys., 39, 439–454, 2021 https://doi.org/10.5194/angeo-39-439-2021 © Author(s) 2021. This work is distributed under the Creative Commons Attribution 4.0 License. The geomagnetic data of the Clementinum observatory in Prague since 1839 Pavel Hejda1, Fridrich Valach2, and Miloš Revallo3 1Institute of Geophysics, Academy of Sciences of the Czech Republic, Bocníˇ II/1401, 141 00 Prague, Czech Republic 2Geomagnetic Observatory, Earth Science Institute, Slovak Academy of Sciences, Komárnanskᡠ108, 947 01 Hurbanovo, Slovakia 3Geophysical Division, Earth Science Institute, Slovak Academy of Sciences, Dúbravská cesta 9, 840 05 Bratislava, Slovakia Correspondence: Pavel Hejda (
[email protected]) Received: 29 January 2021 – Discussion started: 19 February 2021 Revised: 8 April 2021 – Accepted: 9 April 2021 – Published: 17 May 2021 Abstract. The historical magnetic observatory Clementinum 1 Introduction operated in Prague from 1839 to 1926. The data from the yearbooks that recorded the observations at Clementinum have recently been digitized and were subsequently con- Reliable long time series of geomagnetic records are needed verted, in this work, into the physical units of the Interna- for studying the long-term behaviour of the Earth’s mag- tional System of Units (SI). Introducing a database of ge- netic field, for instance its secular variation (Cafarella et omagnetic data from this historical source is a part of our al., 1992). At present, high-resolution direct geomagnetic paper. Some controversial data are also analysed here. In the measurements provide extremely useful information about original historical sources, we identified an error in using the changes in the geomagnetic field. Magnetic and auroral physical units.