But the most interesting thing about Japanese mirrors--the one thing that has made them famous and brought them to the notice of lovers of the curious and the occult--is their reputed _magical_ property. Oriental stories of magic mirrors have been current from the middle ages, most of them wholly childish and absurd. But along with these there have existed accounts, of a more reliable character, of mirrors which are capable of reflecting, in a beam of light that falls on their face, the pattern which they carry on their back. This singular property is no myth, though the true explanation of the phenomenon was long unknown. When first seen, the phenomenon is so startling that it seems almost incredible. You take the mirror into your hand and examine it. Its face is slightly convex, perfectly polished, unless scratched by use or tarnished; and on looking into it you see only your own image, or the objects about you--not a hint or trace of the raised pattern at the back. Now hold up the mirror in direct sunlight, or in the path of a powerful beam of light from some artificial source, such as an electric lamp. It will reflect back the beam, and cast an illuminated patch on the wall or floor, just as any other mirror will do. But on examining this luminous patch you will at once observe--if your mirror is a good one--that the salient features, and sometimes even the fine details, of the pattern on the back are reproduced in the light reflected from the front. Some dozens of Japanese mirrors, most of them quite modern, have passed through the hands of the author for optical examination. Some of these failed to show any magical properties whatever. Others showed the property very well. Others again, which showed nothing at first, were found capable of being converted into magic mirrors by a course of treatment subsequently discovered.
Down to about 1845 these mirrors were excessively rare in Europe, though it is quite possible that they may have occasionally formed part of the stock-in-trade of mediæval conjurors and magicians. Amidst the mass of occult rubbish one may here and there discern statements probably relating to the genuine phenomena exhibited by mirrors of the class in question, having little or nothing in common with the visions to be seen in crystal spheres, or beryls, or in pools of ink. Thus Gaspard Schott, both in his “Physica Curiosa” and in his book on Magic, refers to the Mirror of Pythagoras, in or on which he is said to have written in blood the things which he wished to signify, and which, when turned to the moon, displayed upon the disk of the moon, visibly to one standing behind, the things so inscribed. The “disk of the moon” here referred to may have been simply the luminous patch cast by the reflected moonbeam.