I used to be in the survey instrument repair business. I have worked on instruments dating as old as 1873. I am not familiar with the instrument shown and would suggest taking it to a instrument shop in your area before attacking the brass with any polishing compound. If the instrument has any value, alteration could destroy some value.
The straight knurled knobs and rather straight angular features may suggest it is a more modern day copy, not an orginal of any particular maker.
I have an old instrument someone held up to a buffing wheel and seemingly removed a green deposit. The excess black buffing compound was left in recesses and odd shaped areas. The instrument as manufactured had a green finish applied over the brass, it was not discolored brass. The result was an instrument that was intact in every other aspect, including the spider web crossgair, but now the finish was destroyed.