1871). I on the Mirror of Japan and ils Magic Qualily. 20 



where tlicy arc niado no European lias np to the present time been 

 able to obtain, cither from the manufacturers or from men of letters, 

 the information, whicli is so full of interest to us, because the f(jrmcr 

 keep it a secret when by chance they possess it, and the latter gene- 

 rally ignore the subject altogether. I had found many times in 

 Cliiucse books details regarding this kind of mirrors, but it was not 

 of a nature to satisfy the very proper curiosity of philosophers, 

 because sometimes the author gave on his own responsibility an ex- 

 planation that he had guessed at, and sometimes he confessed in good 

 faith that this curious property is the result of an artifice in the 

 manufacture, the monopol}'- of which certain skilled workmen reserve 

 to themselves. One can easily understand this i^rudent reticence 

 when we remember that the rare mirrors which show this phenomenon 

 sell from ten to twenty times as dear as the rest." 



The prevalent idea has been that the phenomenon of the magic 

 mirror was caused by a diiference of density in various parts of the 

 surface, either produced intentionally or accidentally ; and this the 

 lecturer exj^lained arose from two causes, first from the common belief 

 that the patterns on Japanese and Chinese mirrors were, like those on 

 ordinary coins, produced by stamping, the other because the distin- 

 guished European philosophers who had examined into the question 

 had investigated with considerable success experimentally how such 

 mirrors might be made, but they had not, the lecturer thought, 

 directed their attention to the examination of the question — How was 

 the phenomenon in these rare Eastern mirrors actually produced? — 

 obviously a very diiferent question. 



Professor Ayrton mentioned that he and his colleague. Professor 

 Perry, were led to take up the investigation from a very remarkable 

 fact pointed out by Professor Atkinson of Japan, viz. that a scratch 

 made with a blunt iron nail on the back of one of these magic mirrors, 

 although it produced no mark on the face of the mirror which couhl 

 be seen by direct vision, nevertheless became visible as a bright lino 

 on the screen when a beam of sunlight was reflected from the polished 

 face of the mirror. The lecturer mentioned that after trying various 

 experiments with polarised light, &c.. Professor Perry and himself 

 availed themselves of a very simi^le method of investigation, but one 

 which had apparently not suggested itself to previous observers. On 

 one occasion, when some of their students were using lenses to 

 endeavour to make the exhibition of the phenomenon more striking, 

 it occurred to them that the employment of beams of light of different 

 degrees of convergence or divergence would furnish a test for deciding 

 the cause of the whole action. For while, if the phenomenon were 

 due to molecular differences in the surface — the commonly received 

 opinion — the effect would be practically independent of the amount of 

 convergence of the beam of light ; on the other hand, if it, by any 

 chance, were due to portions of the reflecting surface being less convex 

 than the remainder, a complete inversion of the phenomenon might be 

 expected to occur, if the experiments, instead of being tried in ordinary 



