PROBLEMS IN ASTROMETRY: The catadioptric refractor

. For the most precise astrometric work it has proved necessary to use only the great refracting telescope, al- though such an instrument still falls short of perfection. The color curve is so severe that faint companions may become unobservable, or a dependence on spectral type may be introduced. Spectroscopic and spectrographic work are also affected. The author proposes here a revival of interest in the Schupmann medial telescope, redesigned for the requirements of modern researches, and discusses the pros and cons of such an instrument for astrometric applications.