This is the original 31 inch plate glass mirror of the James Keeler Memorial Telescope. The optics were made by John A. Brashear. It is interesting to note that the wide use of natural gas in the glass industries of the late 1800's led to the production of very pure, tough and well annealed plate glass. In reducing tempeture of the annealing ovens the gas by its continous flow Brashear was able to complete a glass works for experiments in optical glass. Natural gas was used throught his oven and an automatic cut-off governed the annealing temperature.