Ye Magick Mirrour of Old Japan

by Silvanus P. Thompson

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.

Again, it is stated that the Italian historian, Muratori, makes two references to magic mirrors, one in the possession of Bishop Bartolomeo of Verona, who was murdered by Mastino della Scala in 1338; the other found in the house of Cola di Rienzo (or Rienzi), which had upon its back the word “Fiorone.” Not having been able to verify the statement from literature available in the British Museum, I am in doubt about the last case. It is much more likely that the mirror bore on its back a large flower, than that it bore the word meaning a large flower.

Except for obscure references such as these, there is no record of real magic mirrors prior to 1832. Yet a few did undoubtedly exist. There were some in the collection of the royal family of Savoy at Turin, which were later examined by Professor Govi. There was one reputed to be magical in Berlin. The great Von Humboldt thought it worth his while, in 1830, to bring this mirror to Paris to show it to his confrères of the Académie des Sciences; but having brought it, found himself unable to show anything. In 1842 several mirrors were brought from Nankin by Admiral Mouchez (commander of “La Favorite”), M. Arosa, and M. Piou. One was in the possession of the Marquis La Grange in 1847.

With the opening of Japan to the commercial world, in 1867, came the export of mirrors amongst other articles of metal-work; amongst them some that were of magic quality. One was displayed in 1876 in the Loan Collection of Scientific Apparatus in the western galleries of the South Kensington Museum. The official Catalogue (p. 927) thus describes it: “983 c. Magic Mirror. [Exhibited by] Robert von Tarnow. This mirror is a curiosity, and consists of a brass concave disc with finely polished surface. At the reverse rough side there are several Arabic (sic) characters in relief. By exposing the polished surface to the rays of the sun in such a way that they reflect them on the wall, the Arabic figures of the reverse side of the disc become plainly visible in the reflected light on the wall.” It was this mirror which, in the following year, the present writer had in mind when, writing in “Nature,” he proposed that an investigation should be made into the strange optical property so exhibited. Happily at that time his friend Professor W. E. Ayrton was resident in Japan as Professor in the Imperial College of Engineering at Tokio, and he and his colleague, Professor Perry, at once engaged in an exhaustive research on the subject, in the course of which they not only examined some hundreds of mirrors, but also acquainted themselves on the actual spot with the methods of manufacture, which until then were entirely unknown, or misunderstood. A year or two later, after the publication of the researches of Ayrton and Perry, other researches of an entirely confirmatory character were published in France by M. Bertin. In fact, the scientific investigations may be sharply divided into four periods.

(i.) 1832. Elementary guesses by Brewster and Prinsep, the former of whom ascribed the phenomenon to some supposed molecular changes in the metal at the surface, due to a pattern having been stamped on the front to imitate that on the back, and then ground off. The latter ascribed it more correctly to differences of curvature of surface, but also fell into the error of supposing the ornament to have been stamped.

(ii.) 1844-1853. French investigations by Arago, Julien, Person, and Maillard. Of these investigators Person gave the suggestion of the true cause, namely, minute differences of curvature in the polished surface, a circumstance which he proved by covering the mirror with a piece of paper having a circular hole, about one centimetre in diameter, and which, when moved about over the mirror (in sunlight), caused as a reflected image a spot of light, the size of which varied from point to point of the mirror. He also soldered a narrow slip of sheet metal behind a polished daguerreotype plate, and found that when the latter was slightly bent the image from the front showed a luminous line at the corresponding place. Maillard later adopted Person’s theory, and confirmed it by employing an optician to burnish on the lathe a piece of metal which had raised markings on its back. He also noted that a scratch on the mirror back gives a bright line in the image.

(iii.) 1864-66. Investigations of Govi, in Italy, and his controversy with Brewster thereon. Govi frankly adopted the views of Person, and confirmed them by an experiment based on the mode adopted by the constructors of reflecting telescopes for testing the accuracy of the figure given by the grinding machinery to specula. He caused a magic mirror to reflect upon a screen the image of a fine grating of lines, ruled upon glass with a diamond, and placed close to a brilliant point of light. By the distortions which the mirror produced in these lines he found the whole reflecting surface to be minutely undulated over with slight variations of curvature in complete correspondence with the raised arabesques on the back. These undulations, he observed, escape notice when one is looking into the face of the mirror because they are so gentle, and are such that, to perceive them, we require organs that are more delicate than our own. On the publication of this account, and of a translation of it in the “Scientific Review” for 1865, Sir David Brewster wrote to say how, in 1832, he had explained the phenomenon as being due to differences of density or other quality of molecular structure, or to fine scratches produced by trickery, and doubting Govi’s explanation. He declared that similar phenomena had been produced by stamping patterns into the face of brass and grinding them down to be invisible on inspection. He considered the only way in which they could be proved to be due to delicate differences of curvature was either to show that they disappeared on re-surfacing the mirror with a soft speculum-tool, or by taking an exact cast from the mirror, and seeing whether this also had magic properties. Govi thus challenged, at once disproved Brewster’s position, and established his own by showing that the character of the image, white lines on dull ground, is changed to that of dull lines on a brighter ground, by simply interposing in front of the mirror a convex lens. This effect can only be produced by difference of curvature of surface. Further, Govi performed the following striking experiment. Taking a Japanese mirror which ordinarily showed no magic effects, he heated it behind with a spirit lamp, when at once it acquired magic properties. He further improvised with a piece of daguerreotype plate, and a metal ring which he soldered to the back at as low a temperature as possible, a mirror which showed the same effects when, by heating, there arose an unequal expansion between the thin and the thick parts.

Plate III.

(iv.) 1878-80. Researches of Ayrton and Perry, and those of Bertin, of Laurent, and of Muraoka. First, Ayrton and Perry set about procuring mirrors from the shops in Japan, and found that the vendors were in many cases wholly ignorant of the existence of the magic property. Further, the mirror makers could not say how the mirrors became magic, nor which of their mirrors were such; or they gave explanations subsequently found false, declaring the effect to be produced by application of an acid paste to etch the face prior to polishing. The investigators then, having procured some good mirrors, proceeded to test the various possible suggestions as to the origin, such as the supposed difference of density, or of molecular constitution, or the supposed inlaying of the face with inferior metal, or to supposed concealed scratches on the surface, or, finally, to differences of curvature. By simple experiments in which bright light was caused successively to fall upon the mirror in diverging, parallel, or converging beams, it was demonstrated beyond question that the last-named cause was the true one. The whole phenomenon is explained if once it could be established that the surface over the thick parts is flatter (less convex, or even actually slightly concave) than the surface over the thin parts. Using a large convex lens to converge sunlight that had been reflected from a mirror, they showed that by merely altering the distance of the screen on which the image was received they could make the image either positive or negative at will; a result impossible on any other hypothesis than that of differences of curvature of surface. This being established, they then investigated the process of mirror manufacture, to ascertain how these delicate inequalities of surface arise; and they found it to be due to an accident, or incident, of manufacture. All the finished Japanese mirrors may be observed to be slightly convex in the face. They are cast in moulds, the surface of each half of which is quite flat save for the ornament incised on the mould for the back. The following is Ayrton and Perry’s description of the process of casting.