Paris telescope. Newtonian reflecting telescope installed at the Paris Observatory, France, during the 1860s. It had a 1.2 meter (48 inch) diameter mirror. This was the first large telescope mirror to be made of glass coated with silver deposited chemically in a method devised by the German chemist Justus von Liebig. The mirror was much better than those made of polished copper alloy, but the telescope's poor mounting made it nearly useless.