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Profs. W. E. Ayrton and John Perry. [Dec. 12, 



created more interest in Europe than it has in Japan) possessed by 

 certain Japanese and Chinese mirrors of apparently reflecting from 

 their polished faces the raised characters on their backs. 



It was for this third reason, the interest that such mirrors have long 

 possessed for the student of science, that our attention was drawn to 

 the subject, and it has been in this direction that our inquiry has been 

 chiefly directed. The results of our investigation we propose giving 

 in the present paper, reserving for a subsequent occasion* some remarks 

 on the Japanese mirror as an object of worship, and the position it 

 holds on the toilet table of a Japanese lady. 



The mirror of the Far East is too well known to need an elaborate 

 description ; suffice it for the present to observe that it is generally 

 more or less convex on the reflecting side, usually made of bronze, 

 polished with a mercury amalgam, and having at its back a gracefully 

 executed raised design, representing birds, flowers, dragons, a geo- 

 metrical pattern, or some scene in Japanese mythical history. Occa- 

 sionally there are in addition one or more Chinese characters (signi- 

 fying long-life, happiness, or some similar idea) of polished metal, 

 in bold relief. To the method of manufacture we shall refer further 

 on, and especially to the mode in which the convexity of the surface 

 is produced; which portion of the manufacture, while playing, as it 

 does, an important part in the magical behaviour of the mirror, is, as 

 far as we are aware, not to be found described in any of the Eastern 

 or Western writings on the subject. 



Just before leaving England, in 1873, the attention of one of the 

 authors was directed to the so-called magic property of certain Eastern 

 mirrors by the late Sir Charles Wheatstone, who explained to him 

 that the Japanese had a clever trick of scratching a pattern on the 

 surface of a bronze mirror which, after being polished, showed no 

 traces of the scratches when looked at directly, but which, when used 

 to reflect the sunlight on to a screen, revealed the pattern as a bright 

 image. This opinion appears to have been shared by Sir David 

 Brewster, since he says, in the "Philosophical Magazine" for 

 December, 1832 :— 



"Like all other conjurors, the artist has contrived to make the 

 observer deceive himself. The stamped figures on the back (of the 

 mirror) are used for this purpose. The spectrum in the luminous area 

 is not an image of the figures on the back. The figures are a copy of the 

 picture which the artist has drawn on the face of the mirror, and so con- 

 cealed by polishing that it is invisible in ordinary lights, and can be 

 brought out only in the sun's rays." 



As the explanation, therefore, appeared to this one of the authors to 

 be so simple, and at the same time so complete, he practically dis- 

 missed the subject from his mind. 



* A lecture at the Royal Institution. 



