Bausch and Lomb antique brass 1.9 mm , 97X,  oil immersion microscope objective. It has an  n.a. of 1.25! It has been visually checked and no signs of oil incursion into interior elements can be seen and it is free from dust, fungus, scratches and element separations. This is one of the nicer old brass objectives I've seen and I don't think it has had the brass cleaned, original patina!  Thank You for Looking!