 Complete the following phrase:  Yerkes Observatorys 40-inch 102 cm refracting telescope has a doublet lens produced by the optical firm Alvan Clark  Sons and a mounting by the Warner  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 