Zenith Telescope

Description:

The "Wanschaff Berlin" inscription on this zenith telescope is that of Julius Wanschaff (1844-1903), a precision instrument maker who established a shop in Berlin in the 1870s. The firm was inherited by Hermann Wanschaff in 1903, and absorbed into Askania AG in 1922.

This instrument was made for the international project to observe the wobble of the earth on its axis. The notion of a polar motion originated with Leonard Euler's 1765 memoir on "The Theory of the Motion of Solid and Rigid Bodies." The first observational evidence of polar motion came from two astronomers, Seth Chandler in the United States (1887) and Friedrich Küstner in Berlin (1888). The International Geodetic Association (now the International Association of Geodesy) organized a coordinated observing program in 1889, with four observing stations in Europe (Potsdam, Berlin, Prague, and Strasbourg) and two in the United States (Rockville, Md., and San Francisco, Calif.).

The polar motion program was formalized in 1899, when the International Geodetic Association organized an International Latitude Service, with a Central Bureau located in Potsdam, and six observing stations, each situated near latitude 39° 08' north. Four of these stations--Mizusawa in Japan; Carloforte in Italy, and Gaithersburg, Md. and Ukiah, Calif. in the United States--had large Wanschaff instruments (108 mm aperture and 130 cm focus). The stations at Tschardjui, Russia, and at Cincinnati, Ohio, had slightly smaller ones (68 mm aperture and 87cm focus). Although the Central Bureau has moved, and various observing stations have come and gone, the project continues to this day.

Ref: Theodor Albrecht, Anleitung zum Gebrauch des Zenitteleskops auf den Internationalen Breitenstationen (Berlin: Centralbureau der Internationalen Erdmessung, 1899 and 1902).

Hermann Wanschaff, Preis-Vernzeichnis über Wissenschaftliche Instrumente (Berlin, 1904/1905).

Encyclopaedia Britannica, 11th edition (Cambridge, 1910), vol. 11, art. "Geodesy," p. 611.