This is a simple three-armed brass spectroscope with one glass prism, with a black iron tri-leg base, and a black iron tube to provide gas a flame. The “P. Desaga / Heidelberg / No. 661” inscription on the eye tube refers to Peter Desaga, the University of Heidelberg instrument maker who, in the late 1850s, made the instrument that Robert Bunsen and Gustav Kirchhoff used for their pioneering work in spectroscopy.
This example resembles the instrument depicted in Henry Draper, “The Spectroscope and its Revelations,” The Galaxy (June 15, 1866): 303-319; reprinted in Scientific American (July 7, 1866): 17-18.