i'tO Sir D. Brewster's Account of a curious Chinese Mirror. 



in number, and a little confused in the centre opposite the 

 eye of the button. On the back of this button several words 

 were deeply stamped, but these words did not appear in the 

 reflected image. I have since examined several varieties of 

 such buttons, and I find that they almost all give either radia- 

 tions or great numbers of narrow concentric rings, (and some- 

 times both), whose centre is the centre of the button, and the 

 smallest one of which is always like a dimple in the centre. 



Upon examining the surface of these buttons in the sun's 

 light and at the edge of a shadow*, I have invariably been 

 able to see the same rings excavated in the polished face that 

 appeared in the luminous image, which it reflected. They 

 obviously arise from the button being finished in a turning 

 lathe, and the rings are produced by the action of the polish- 

 ing powder, or probably, in some cases, they may be the 

 grooves of the turning tool, which have not been obliterated 

 by the subsequent processesf . 



These facts will, I presume, furnish us with the secret of 

 the Chinese mirror. Like all other conjurors, the artist has 

 contrived to make the observer deceive himself. The stamped 

 figures on the back are used for this purpose. The spectrum 

 in the luminous area is not a7i image of thejigures on the back. 

 The figures are a copy of the picture which the artist has 

 drawn on the face of the mirror, and so concealed by polishing, 

 that it is invisible in ordinary lights, and can be brought out 

 only in the sun's rays. 



Let it be required, for example, to produce the dragon de- 

 scribed by Mr. Swinton, as exhibited by one of the Chinese 

 mirrors. When the surface of the mirror is ready for polish- 

 ing, the figure of the dragon may be delineated upon it in ex- 

 tremely shallow lines, or it may be eaten out by an acid much 

 diluted, so as to remove the smallest possible portion of the 

 metal. The surface must then be highly polished, not upon 

 pitch, like glass and specula, because this would polish awaj' 

 the figure, but upon cloth, in the way that lenses are some- 

 times polished. In this way the sunk part of the shallow lines 

 will be as highly polished as the rest, and the figure will only 

 be visible in very strong lights by reflecting the sun's rays from 

 the metallic surface. 



When the space occupied by the figure is covered by lines 

 or by etching, the figure will appear m shade on the wall, but 



• By this method the figure in the Chinese mirror could be rendered 

 visible beneath its polish. 



t In polished steel buttons the reflected light is crowded with lines run- 

 ning at right angles to each other, and clearly indicating the cross strokes 

 by which they have been ground and polished. 



