This appears to be some sort of cosine function optical probe using a small opal hemisphere attached to a fiber optic probe. The distal end of the fiber optic terminates in a housing with a flat slit output, presumably to illuminate the entrance slit of a monochromator or spectrometer.
The slit housing is 1.314 inches in diameter and keyed for proper slit orientation. The dimensions of the slit output are 0.025 inches by 0.385 inches. Overall length including both housings is 36 inches. Condition is excellent.
Location MB 141
Photo set 991