Ye Magick Mirrour of Old Japan

by Silvanus P. Thompson

In repeating the experiments on heating, the author found a very singular effect to be produced by warming (with a flame) the back of a thin piece of mirror glass while it reflected from its face a grating of luminous lines thrown upon it by a lamp as described above. As the flame was passed rapidly across the back, the whole pattern appeared to heave, as though a wave had passed along it.

Plate VI.

He was able also to reproduce writing in luminous lines on a screen or wall by the following device. A piece of thin sheet lead (tea-chest lead) was laid on a bed of blotting-paper; and upon this was written with a common lead pencil any word desired, which therefore was slightly indented into the lead. The sheet was then pressed lightly against an ordinary piece of mirror glass and heated from behind by pressing against it a disk of hot metal. The written letters touching the back of the mirror warmed it, and made it curve at these parts. Hence, placed in an appropriate divergent beam of light, it threw the handwriting upon the wall.

Following the hint given by Bertin’s research upon the effect of bending mirrors by air-pressure at the back, the author finds that a similar effect is even more powerfully produced by simple mechanical pressure. He took a mirror which, though it had an excellent reflecting face and a well-raised pattern on the back, showed no magic properties, and having clamped it in a wooden frame, he applied screw pressure behind to force against the back a slightly convex piece of soft wood covered with a pad of cloth. On turning the screw the mirror at once became magic, and was found, even after the screw had been released, to retain some part of its magic property. It was again distorted by screw pressure, and while violently bent was heated to anneal it somewhat. On removing the pressure it was found to retain permanently all the qualities of a good magic mirror, though it is slightly more convex than mirrors ordinarily are. Since then it has been found that many mirrors which, when purchased, showed no magic properties, can be converted into magic mirrors, some by application of screw pressure, some by mere bending by hand over the knee, some by burnishing under pressure the pattern at the back.

Engineers are so familiar with the circumstance that when metal castings are rapidly cooled the internal parts are in a state of strain, that they are not astonished to find that after a casting has been surfaced accurately on one face the figure may alter slightly by the mere release of internal strains in the slow annealing of time. It is quite possible that this too occurs with Japanese mirrors, and that some of them may acquire with the mere lapse of time magic qualities that they do not show at first when newly polished.

There appears to be another species of magic mirror, of which few examples are known, having the property of showing in the face a pattern entirely different from that on the back. Three such are mentioned by Ayrton, though it does not seem that he himself had inspected any of them personally. One of these, which he states to exist at Kamakura, the old capital of the former Shoguns, is a religious mirror about four inches and one-fifth high, by three and a half wide, held in great reverence. In the polished surface, when looked at very obliquely, is seen the image of a Buddhist priest. The pattern on the back is a rosary in high relief with a branch of plum-blossom, and a crescent moon rising out of the sea as a background. It is said that this optical effect is produced by chemically etching the surface with an acid paste, and then repolishing. Professor Ayrton, who had two mirrors made thus by a Japanese mirror-maker, found that if the face of a mirror that had so been etched was repolished until every trace of the marks disappeared in direct or oblique vision, they then entirely disappeared also from the image cast by the mirror in reflecting a beam of light upon a screen. He greatly doubted whether chemical means could produce a mirror possessed of true magic properties. The cause of the phenomena of the Kamakura mirror and its congeners—should the facts be established as narrated—therefore remains still to be explained.

Though in the case of the ordinary Japanese mirrors science completely explains what would otherwise seem to be a most mysterious and unaccountable phenomenon, the explanation itself involves a very remarkable fact, namely, that there can exist such very delicate and minute differences of curvature in the polished face as to be practically invisible for ordinary purposes, and difficult even of scientific detection, and yet that those minute differences in curvature should be in such exact correspondence to the patterns on the back as to reproduce those patterns in the reflected beams of light. The facts seem so utterly unlikely à priori to be true, that one can only give full credence to them after the most searching scientific demonstration. But is not this, after all, only another example of the truism that when science explains away one mystery she does so by establishing some truth that is itself still more mysterious?

The Mirror of Kamakura.