It was donated to the Institute of Science by the Palatine Elector Charles Theodore.
It is made up of a large magnetic needle for monitoring the variations in magnetic declination, observations that in the XVIIIth century were part of meteorology.
The design of the Mannheim prototype of this instrument can be found in the first volume of the Ephemerides Societatis Meteorologicae Palatinae. The marble base on which the declination compass lies bears the inscription Carolus Thedorus Elector Palatinus / Anno 1780.
In his 1843 inventory Gaetano Ceschi described it as: "A declination compass made in Augsburg by G.F. Brander, on a marble base that can be levelled by means of three screws, with a 60 degree arc, half to the east and half to the west. A metal alidade which revolves around the needle’s suspension point has a vernier at the end which can supply the three arcminutes of the graduation. A mirror tilted at 45 degrees serves to make clearer the coinciding of the Needle with the point zero line of the vernier. A glass-top case protects the needle from outside interferences. A second spare Needle."
The name of the craftsman is engraved on the instrument’s case: G.F. Brander fecit Aug. Vind.

E. Baiada (1986).
R.C. Brooks (1991), p. 146.
Ephemerides Societatis Meteorologicae Palatinae (1783).