This 18th century theodolite is part of the Observatory Collection. It was created by Rudolf Wolf (1816-1893). He was a professor of astronomy, head of the Semper Observatory, director of the library of the Polytechnic (present-day ETH) and collector of astronomical instruments. He created an inventory for his collection in 1873. Unfortunately, the manner in which the digitalised theodolite was incorporated into the collection is not stated here. Rudolf Wolf received many of his instruments as gifts or bought them from another collector.

The Observatory Collection includes around 250 astronomical instruments. The collection was initially transferred to the ETH library when the observatory was closed in the 1980s, then incorporated into the collection of scientific instruments and teaching aids when it was established in 2019.

G.F. Brander, manufacturer

The digitalised theodolite was manufactured by Georg Friedrich Brander (1713-1783). Brander was an important manufacturer of scientific instruments. His workshop was located in Augsburg, which, alongside Paris, London and Leipzig, was considered a centre of instrument making in the 18th century. Even then, Brander’s instruments were considered equivalent to those from England and France.¹

Brander built instruments for various disciplines, such as geodesy, astronomy and physics. This was not unusual for the time: Until the early 19th century, instrument makers did not specialise in one discipline or type of instrument.

Germany’s first reflecting telescope was built by Brander as early as 1737. This was a great achievement for Brander, who, at age 24, was still very young at the time. His working method consisted mainly of improving existing objects. His instruments were often even better than the originals. From 1761 onwards, he delivered his instruments to Munich, and Berlin as well as to Switzerland, e.g. to the physics societies in Vaud and Zurich. The workshop’s delivery catalogues suggest that Brander must have had several employees, as he was able to produce a great deal. Unfortunately, very little is known about this.²

One of Brander’s daughters married Christoph Caspar Höschel in 1774. The latter then became his business partner and the objects were signed “Brander & Höschel” from 1775 onwards. After Brander’s death in 1783, Höschel continued to run the workshop alone. However, he was unable to match his father-in-law’s success. No evidence of the successor company exists after 1850, but Brander’s tradition was continued in Munich by the workshops of Reichenbach and Fraunhofer.³

The theodolite

The digitalised theodolite is dated to around 1752, based on similar objects. Brander exerted a significant influence on the development of theodolites for over 30 years. Theodolites were used not just for land surveying, but also for astronomical measurements. Horizontal and vertical angles could be determined using this theodolite. It is equipped with a double-lens Kepler telescope, but has an additional empty holder (annotation 4 in the 3D model). A second telescope could be attached there for backward sightings. The Kepler telescope combines two converging lenses of different focal lengths and was used for both astronomical and geodetic surveys.⁴ A level as well as the foot screws are also missing from this theodolite.⁵