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LI II. A New Mode of making Magic Mirrors. 

 By J. W. Keabton*. 



THE first explanation that occurred to me on seeing the 

 Japanese mirror about fourteen months ago was that the 

 face might bear directly invisible differences in polish, which 

 a powerful beam of light would probably convert into visible 

 ones by reflexion on to the screen. To produce such minute 

 differences, it was my intention to take pairs of different 

 metals closely agreeing in colour and reflective power, as 

 silver and platinum, and to deposit electrically in the form of 

 some easily recognizable figure a thin coating of the one 

 metal on a groundwork of the other. Yery faint mercuric 

 staining of bright metallic surfaces was also contemplated. 

 These ideas, however, resolved themselves into a test much 

 simpler, yet involving the same principle. A piece of metal 

 was so polished that in subdued daylight a cross, more finely 

 burnished than the general surface of the plate, could just be 

 distinguished. Reflected on to the screen, the figure came 

 out exceedingly faint ; and this fact, apart from the con- 

 sideration that figures so produced could have only a pre- 

 carious existence, was sufficient to condemn the hypothesis 

 in question. 



This result has a bearing upon another hypothesis — one 

 worthy of prompt burial with the quiddities and essences of 

 the purely deductive method, viz., that the magic-mirror 

 phenomena are due to local molecular rearrangements in the 

 reflecting surface, brought about by unequal cooling of the 

 mass of the mirror. Now, since it is held that the regu- 

 larity or convexity of the surface is not thereby affected, this 

 molecular rearrangement can put itself in evidence optically 

 only by reflecting more or less light than the parts of the 

 surface unaffected by irregular cooling. But it has been 

 shown that with figures so pronounced as to be directly 

 visible, the electric beam is powerless to produce results com- 

 parable in intensity with those given by the Japanese mirror ; 

 much less will directly invisible figures of the type under 

 reference come up to the required standard. 



The plate used in the foregoing experiment, whilst fur- 

 nishing no clue in virtue of its polished figure, yet presented 

 evidence that pointed clearly in the direction where a solution 

 of the problem was to be found. Strikingly well-defined 

 lines and dapplings of light an ere thrown on the screen by 



* Communicated by the Physical Society : read January 26, 1894. 



