The 1873 inventory contains the following description: "A repeating circle by Reichenbach and Utzschneider with silver limb one foot in diameter, divided 4" by 4" by means of 4 verniers. The two telescopes have object lenses of 18 line aperture and 16 inch focal length. The instrument is fitted with wooden legs [Inv. MdS-157] and a carrying case [not found]." On the limb is the signature Reichenbach, Utzschneider und Liebherr in Münich.
The repeating (or universal) circle - so called because it can measure angles in any plane - consists of two graduated circles, one inside the other. On the inner circle is fitted a telescope for sighting point zero while another telescope rotates on the outer circle for measuring the angle under examination. Once the two points have been centered, the outer circle can be locked in the desired position with a stop that can be moved like a micrometer. The angle is then read off on the graduated circle.
The instruments of Reichenbach and co-workers were accurate to almost one arcsecond.
The circles can be turned over for use as an altazimuth instrument. A tripod supports the apparatus and a bubble level [Inv. MdS-89] is used for setting it up. Two counterweights are attached to help balance the instrument.
The ease and accuracy in computing right ascensions and declinations with the repeating circle led to its being used in practically all astronomical observatories in the first half of the XIXth century for both celestial coordinate and topographical measurements.
The mechanical workshops of the Astronomical Observatory in Rome reconstructed the eyepiece attachments of the two telescopes in 1993. The walnut tripod support was restored in the same year by S. Salemme (Imola).
J.A. Bennett (1987), pp. 159-160.
M. Calisi (1991), p. 38.
M. Daumas (1953).
E. Miotto, G. Tagliaferri, P. Tucci (1989), p.53.
J.A. Repsold (1908 and 1914).
G.L’E. Turner (1991), p. 224.