The great nineteenth century refractors

Abstract

The first modern refractor was built in 1824 by Fraunhofer; its diameter was 23 cm. The sizes of the largest refractors grew linearly with time, culminating in the 102-cm Yerkes telescope (1897) and the 125-cm horizontal refractor with siderostat for the 1900 Universal Exhibition in Paris. This was the end of the giants; however long-focus photographic or visual refractors with diameters 60-70 cm were still being constructed until 1972. In parallel, many short-focus, wide field astrographs were built after 1893. We recall the scientific uses of the large refractors, and discuss why these cumbersome and expensive instruments were not dethroned by the silvered-glass reflecting telescopes until late, in spite of the advantages of the latter.