1878.] 



The Magic Mirror of Japan. 



147 



and to cause the face to present a smooth surface for the subsequent 

 polishing. 



In the case of thick mirrors the convexity is first made by cutting- 

 with a knife, and the "distorting rod" applied afterwards. But in 

 connection with this cutting process of thick mirrors there is one 

 verv interesting point. If the maker finds on applying from time to 

 time the face of the mirror to a hard clay concave pattern, and turn- 

 ing it round under a little pressure, that a portion of the surface has 

 not been in contact with the pattern, in other words, that he has cut 

 away this portion too much, then he rubs this spot round and round 

 with the megebo until he has restored the required degree of convexity. 

 Here again then scratching on the surface produces convexity. 



Now, why does the scraping of the " distorting rod " across the face 

 of the mirror leave it convex ? During the operation it is visibly 

 concave. The metal must receive then a kind of "'buckle," and spring 

 back again so as to become convex when the pressure of the rod is 

 removed. It might in such a case reasonably be expected that the 

 thicker parts of the mirror would yield less to the pressure of the rod 

 than the thinner, and so would be made less convex, or even they might 

 not spring back, on the withdrawal of the rod, and so remain actually 

 concave. Again, since we find that scraping the face of a mirror is 

 the way in which it is made convex, and the back therefore concave, 

 we might conclude that a deep scratch on the back would make the 

 back convex and the face slightly concave. Such a concavity, as we 

 have proved, would explain the phenomenon of the bright line appear- 

 ing in the reflection of sunlight on the screen which was observed by 

 Professor Atkinson to correspond with the scratch on the back. 



It appears then that the magic of the Eastern mirror results from 

 no subtle trick on the part of the maker, from no inlaying of other 

 metals, or hardening of portions by stamping, but merely arises from 

 the natural property possessed by thin bronze of buckling under a 

 bending stress, so as to remain strained in the opposite direction 

 after the stress is removed. And this stress is applied partly by the 

 " distorting rod," and partly by the subsequent polishing, which, in an. 

 exactly similar way, tends to make the thinner parts more convex than 

 the thicker. 



Polishing. — After the scratches produced by the megebo are removed 

 the mirror is first polished with a whetstone called either iyodo, 

 " whetstone from the province of Iyo," or shiroto, "white whetstone." 

 Afterwards a whetstone called tensMmado, "whetstone from the pro- 

 vince Tsushima," or the powder to-no-ko, previously described, is used. 

 Thirdly, a piece of charcoal, prepared from the ho tree (Magnolia 

 hypoleuca) is rubbed over the surface. The face now becomes fairly 

 smooth, but it still generally contains some few cavities ; these the 

 maker fills up from a stock of copper balls of various sizes which he 



