Yerkes Observatory's 40-inch (102 cm) refracting telescope has a doublet lens produced by the optical firm Alvan Clark &amp; Sons and a mounting by the Warner &amp; Swasey Company. It was the largest refracting telescope used for astronomical research. In the years following its establishment, the bar was set and tried to be exceeded; an even larger demonstration refractor, the Great Paris Exhibition Telescope of 1900, was exhibited at the Paris Universal Exhibition of 1900.