a name given by some authors to the metallic spheres used in optics. These, according to Cardan, are made of three parts of brass, one part of tin, and one of silver, with an eighteenth part of antimony; but most either totally leave out the silver, or add only a twenty-fourth part, to save the expense. There are many other methods, directed by several authors; but most use arsenic and tartar mixed with the metals. These are afterwards to be polished with emery, rotten-stone, putty, and the like.