A universal instrument functions as altitude and azimuth instrument. Here,
however, the telescope is "broken"—that is, the eyepiece is located
at one end of the horizontal axis. The form originated in the Mathematical–Mechanical
Workshop established in Munich in 1804. It was probably designed by Traugott
Leberect Ertel (1778–1858), who joined the firm around 1812, and who became it’s
sole proprietor around 1820. The earliest evidence of the universal instrument
comes from the noted astronomer and geodesist, F. G. W. Struve, who ordered an
instrument of this sort in 1821, used it to survey the Russian province of
Livonia (present day Lithuania), and described it in print. Ertel began
advertising universal instruments in 1824 (at which time it cost 1600 fl.), and
the firm was still offering them at the end of the century.
Ref:
F. G. W. Struve, "Ueber das Universalinstrument von Reichenbach und
Ertel als Horizontalwinkelmesser," Astronomische Nachrichten 2
(1824): 431–440, 451–454, 457–464.
F. G. W. Struve, "Vereiningung der Beiden, in den Ostseeprovinzen und in
Litthauen Bearbeiten Bogen der Russischen Breitengradmessung," Recueil
des Actes de l’Academie imperiale des Sciences de St. Petersbourg 2
(1833): 401–425.
"Verzeichniss derjenigen Instrumente, welche in dem mathematisch–mechanischen
Institute (von Reichenbach und Ertel in München) um, nachstende Preise
verfertigt werden," Astronomische Nachrichten #68 (1824–25): 374–375.
