From Theodolite to Spectral Apparatus: Joseph von Fraunhofer and the Invention of a German Optical Research-Technology

Abstract

One of Joseph von Fraunhofer’s (1787–1826) greatest contributions to technical optics had its roots in ordnance surveying. Fraunhofer, the German territories’ leading optician and optical-glass manufacturer of the period, needed an apparatus that could measure angles very precisely, as he wished to determine the refractive and dispersive indices of optical glass specimens as accurately as possible. Theodolites were the answer, as Georg von Reichenbach, co-owner of the Optical Institute and co-founder of the Mathematico-Mathematical Institute of Munich, was the builder of Europe’s leading theodolites for the joint Bavarian and French Bureau of Topography and the Bavarian Bureau of Land Registry. Reichenbach had devised a new method for the dividing machine (Teilmaschine) that successfully divided a circle into equal parts with an unprecedented precision (Engelsberger 1969; Reichenbach 1821). Once the amazingly precise dividing machine had been constructed, Reichenbach turned to his main goal: the construction of precision theodolites for the ordnance surveying projects (and later Land Registry projects) undertaken in Bavaria during the first decade of the nineteenth century (Reichenbach 1804). These theodolites, as mentioned above, were used by ordnance surveyors in their triangulation projects. A base line was established (usually several miles in length), and by measuring angles subtended by the two ends of the base line and a tall object (a pole on a nearby hill top, for example) with a theodolite, distances could be calculated by using simple geometry. The maps were required for Napoleon’s occupational forces as well as for King Maximilian I’s new property tax program.