A leading nineteenth century instrument-maker in Norway and his astronomical and geodetic instruments

Abstract

Christian Holberg Gran Olsen introduced the European continental standards of scientific instrument making into Norway in 1861, following a four-year tenure with A &amp; G Repsold, Hamburg. This paper lists and discusses the major astronomical and geodetic instruments made by Olsen. The geodetic instruments are now in museums or in university storage. The first universal instrument was extensively used to carry out the Norwegian part of the European Geodetic Arc 1863-1878, both as a theodolite and as a transit instrument for astronomical observations at selected geodetic stations. Other instruments contributed to the mapping of Norway. Olsen's last model was used to determine the position of Fridtjof Nansen's polar ship <italic>Fram</italic> during its three-year expedition (1893-1896) in the Polar Sea. It was also used on other Norwegian polar expeditions during the next thirty years. A copy was made for the first winter expedition to Antarctica, with Belgica in 1897-1899. The first astronomical refractor by Olsen (with a 10.8-cm Steinheil objective lens) was made for Bergen Observatory in 1869. Its current whereabouts have been investigated, but the instrument has not been found. Two larger refractors have been successfully searched for. A 13.2-cm Merz refractor with mounting by Olsen, made for the University Observatory in Christiania (Oslo) in 1883, exists in refurbished condition. The largest refractor, with a 36.0-cm objective lens by Olsen (7 metres focal length), was the centrepiece in what appears to be the first astronomical observatory in Europe founded and operated exclusively for the public on a commercial basis. When erected in 1885, the refractor of the Peoples' Observatory in Oslo was unsurpassed in size in Scandinavia, even at professional observatories.