For this purpose, a wooden three-sided box must be prepared, and through the open part may slide the various drawings to be used, as B. Connected with this, there must be a pillar, C, and a horizontal bar holding a tube, D, having in it a glass placed exactly over the centre. The change is partly dependent on the glass, the sides of which are flat and diverge from its hexagonal base upwards, to a point in the axis of the glass, like a pyramid, E, forming an isosceles triangle. All that is now necessary to the completion of the change, is in the border of the drawing, in which the various parts required for the new figure are cleverly introduced; so that when the distance of the glass from the eye is rightly adjusted, each angular side will take up its portion from the border, and present to the eye the various parts in an entire figure. The shape of the glass prevents the appearance of any particular figure in the centre, as the eagle, for instance; while the lion, arranged in portions and drawn on the circle of refraction at six different parts of the border, yet artfully disguised by blending with it, the transformation will be completely produced. A paper has lately been read to the Academy of Sciences at Paris, by M. Stanislaus Julien, on the metallic mirrors made in China, and to which the name of “magic mirrors” has been given. Hitherto all attempts by Europeans to obtain information as to the process, in the localities where they are manufactured, have proved failures, some of the persons applied to being unwilling to reveal the secret, and others being ignorant of the process. These mirrors are called magical, because, if they receive the rays of the sun on their polished surface, the characters, or flowers _in relief_, which exist on the other side, are faithfully reproduced. The following information has been obtained by M. Julien, from the writings of an author named Ou-tseu-hing, who lived between 1260 and 1341:--“The cause of this phenomenon is the distinct use of fine copper and rough copper. If, on the under side, there be produced, by casting in a mould, the figure of a dragon in a circle, there is then engraved deeply on the disc a dragon exactly similar. Then, the parts which have been cut are filled with rather rough copper; and this is, by the action of fire, incorporated with the other metal, which is of a finer nature. The face of the mirror is next prepared, and a slight coating of tin is spread over it. If the polished disc of a mirror so prepared be turned towards the sun, and the image be reflected on a wall, it presents distinctly the clear portion and the dark portion, the one of the fine, and the other of the rough copper.” Ou-tseu-hing states, that he had ascertained this by a careful inspection of the fragments of a broken mirror.