the spreading the plates over with quicksilver, after they have been polished, in order to reflect the image. The mode in which it is performed may be shortly described. A thin blotting paper is spread on the table, and sprinkled with fine chalk, and a fine lamina or leaf of tin, called foil, is laid over it; upon this is poured mercury, which is to be distributed equally over the leaf; a clean paper is then laid upon the mercury, and over that the glass plate, which is pressed down with the right hand, and the paper gently drawn out with the left. This being done, the plate is covered with a thicker paper, and loaded with a greater weight, that the superfluous mercury may be driven out, and the tin adhere more closely to the glass; and when it is dried, the weight is removed, and the looking-glass complete.