The best mode of mixing the component metals of t!,is alloy appear* to be tt meiteach separately, and then to add the tin to the copper at the lowest stiniiu; 'ettipeiature. To complete the combination, the alloy" is again melted very gradually by glueing the metal in tiie crucible almost as soon as lh- iir? is lighted. The hardness of this allov. compared with toe extreme softness oi' the metals, ya'es us an example of the chemical changes effected by their combination. Thus, the I speculum metal, as used by Lord Rosse, is to- i tally devoid ot malleability, and from its hardness cannot be acted on by the file. His speculum consisted of lour atoms of chemical combining proportions of copper to one of tin; or, by weight, 126 4 copper to S8'9 tin. This alloy, which is a true chemical compound, is oi a brilliant white bistre, its specific gravity i-rSli, nearly as hard as steel, and almost,as j brittfeas 6eii!in*-wax. The: speculum is 6j feet in diameter 5 inches thick.. It was east open, grouti'l with, emery, placed on a table in a cistern filled with water at a temperature of 55 Fah., polished with red oxide of iron, procured by precipitation from green vitriol, or sulphate of iron, by water of ammonia.