i86 



NATURE 



[Dec. 26, 1878 



faces. — Prof. Holden describes certain cloud-shaped forms 

 (obscuring the smaller forms of Janssen) observed on the sun's 

 disc on September 16, and cites a like observation made by 

 Prof. Langley, in 1873, ^^° thinks the effect chiefly due to our 

 own atmosphere, while disposed to admit the possibility of some 

 obscuration in the sun itself. — A pseudomorph after anorthite, 

 from Franklin, New Jersey, is described by Prof. Roepper ; 

 and Prof. Verrill gives an account of recent additions to marine 

 fauna of the east coast of North America. — There is also a 

 notice of Edison's sonorous voltameter. — Prof. Marsh's import- 

 ant contribution on the principal characters of American Jurassic 

 dinosaurs has been previously referred to in these columns. 



Morpholo^isches Jahrbuch, vol. iv., Part 3. — Studies on the 

 innervation of the hair-bulbs of domestic animals, by R. Bormel, 

 70 pages, 3 plates. — On Gloidium quadrifidum, a new genus of 

 Protista, by N. Sorokin. — The development of the knee-joint 

 in man, with remarks on the joints in general, and the knee- 

 joints of vertebrates, by A. Bernays. — The skeleton of the 

 Alcyonaria, by G. von Koch, including a minute description of 

 the skeleton in each genus, a general account of it, and a new 

 systematic arrangement, 33 pages, with 2 plates. — C. Hasse con- 

 tinues his studies on fossil vertebrae ; this part is devoted to their 

 histology, and is illustrated by 4 plates. 



'" Zeitschrift fiir -^inssenschaftliche Zoologie, vol. xxxi. Part 2. — 

 Contribution on the Julidse, by E. Voges, dealing very consider- 

 ably with the tracheal system and its development. There are 

 descriptions of many new species of Julus, Spirostreptus, and 

 Spirobolus ; 68 pages, 3 plates. — On the development of the 

 blastoderm and the germinal layers in insects, by N. Bobretzky, 

 with figures chiefly of Porthesia chrysorrhaa . — On the genus 

 Brisinga, by H. Ludwig. — On Aspidura, a mesozoic genus of 

 ophiurid, by Hans Pohlig. — On the structure and development 

 of sponges, Part 5, by F. E. Schulze ; another most valuable 

 contribution, the author having now completely followed the 

 development of Sycandra raphanus, 34 pages, with 2 beautiful 

 plates. 



Parts 3 and 4 in one. — On the cerebral sulci in Ungulata, by 

 Julius Krueg ; the paper deals very largely with the foetal deve- 

 lopment of the convolutions, 50 pages, 4 plates. — Contributions 

 to the anatomy of Ophiurans, by Hubert Ludwig, treating espe- 

 cially on the skeleton of arm and mouth, and the sexual organs, 

 50 pages, 4 plates. — On the generative organs oiAsterina gibbosa, 

 by Hubert Ludwig, i plate, — An account of the anatomy of 

 Magelona, an interesting form, by Dr. W. C. Mcintosh, of St. 

 Andrews ; translated from English for the journal, 72 pages, 10 

 plates. — On some cases of parasitism among Infusoria, by J. 

 van Rees. — Brief notes on the development of Anodon, by C. 

 Schierholz. 



SOCIETIES AND ACADEMIES 

 London 



Royal Society, December 12. — "The Magic Mirror of 

 Japan," Part i, by Professors W. E. Ayrton and John Perry, 

 the Imperial College of Engineering, Japan. Communicated 

 by William Spottiswoode, M.A., Treas. R.S., &c. 



The President stated that Prof. Ayrton had agreed to give, 

 in the Friday evening discourse on January 24, at the Royal 

 Institution, a full account of Japanese mirrors, so that on the 

 present occasion he understood the authors of the paper merely 

 proposed to enter very shortly into the subject. 



Prof. Ayrton commenced by remarking that mirrors in Japan 

 held a very high position, and constituted the most prominent 

 feature in the Japanese temples, taking the place of the cross in 

 Roman Catholic countries, and that the principal mirror in the 

 Imperial Palace ranked higher than even the Emperor himself. 

 He referred to the important place the mirror held in the very 

 limited furniture of a Japanese household ; to the respect at- 

 tached to it by the women, and to the fact that while the sword 

 was considered as "the soul of the samurai" (or two-sworded 

 class) the mirror was looked on as "the soul of the woman." 

 He next showed experimentally the so-called magic property pos- 

 sessed by certain rare bronze mirrors, sold by the Chinese at about 

 twenty times the cost of the ordinary mirrors of that country, 

 and which consisted in these mirrors being able to reflect from 

 their smooth polished faces the raised patterns of birds, flowers, 

 dragons, or Chinese letters with which their backs were adorned. 

 He stated that he had found this property to be possessed by a 

 very small percentage of the Japanese mirrors which he had 



experimented on, but that its existence was quite unknown to 

 the people of that country. The phenomenon had been known 

 in China for centuries, and that, therefore, while he showed it 

 experimentally to the Fellows, he did so in case there might be 

 some there who had never seen it, in consequence of these magic 

 mirrors being rare ; but he desired it to be remembered that it 

 was not the phenomenon itself but the explanation of it which, 

 he had the honour of bringing before them as new. 



After citing all the possible ways in which this curious reflect- 

 ing power could be accounted for, and referring to a number of 

 printed notices that had at various times appeared of the magic i- 

 mirror, the majority of which were accompanied with a theoreti- || 

 cal explanation, he remarked that as the authors had apparently m 

 not made direct experiments with the mirror itself to elucidate 

 the cause of the phenomenon, but rather to have satisfied them- 

 selves with endeavouring to find out how it could be reproduced 

 in Europe, it was not to be wondered at that many of the sug- 

 gested possible explanations were very far from the truth. Up 

 to the present time, he believed, the idea of inequality of density 

 of the surface of the metal mirror produced naturally in cooling, 

 or in the supposed process of stamping, seemed to have found 

 most favour in the West, while the belief that this variation in 

 density arose from trickery on the part of the maker was the 

 view entertained in China. Sir David Brewster and Sir Charles 

 WTieatstone, on the ether hand, who also thought that trickery 

 was the explanation, believed the artifice to consist in the maker 

 skilfully scratching on the face of the mirror, before polishing, ^ 

 lines exactly corresponding with the pattern on the back. 9 



Prof. Ayrton next described what was the explanation of the ^ 

 phenomenon his experiments, made during the winter of 1877-78, 

 had led him to, viz., that there existed extremely slight irregu- 

 larities in the curvature of the polished surface (quite invisible to 

 direct vision), of such a nature that the thicker parts, corresponding, 

 of course, with the raised patterns en the back, were flatter than 

 the remaining convex surface, so that there was less dispersion 

 of light from the thick portion than from the thinner. He 

 then described one of a series of diagrams illustrating various 

 experimental arrangements of convergent and divergent beams 

 of light which the authors had availed themselves of, and the 

 use of which constituted, he said, the essence of the system of 

 investigation employed by Prof. Perry and himself, and he ex- 

 plained that if his theory of the phenomenon was correct, then 

 placing the screen, on which the reflection of the light from the 

 Japanese mirror was cast, in a certain position, the phenomenon 

 ought to disappear, and again putting the screen in another posi- 

 tion, the phenomenon ought to be inverted ; that is, instead of a 

 bright image on a dark ground, which hitherto had alone been 

 what has been observed by previous investigators, a dark image 

 of the pattern on a bright ground ought to appear. This disap- 

 pearance and absolute inversion of the phenomenon he said he 

 had found to actually take place, but that he was compelled from 

 want of time to leave the experimental exhibition of it for the 

 Royal Institution. Various other facts, such as the necessity of 

 holding the screen rather near, but not very near, the mirror 

 when ordinary sunlight without lenses was employed, was, like 

 the inversion phenomenon just referred to, shown to be explain- 

 able only on the inequality of curvatiure theory, and not on the 

 inequality of density theory. 



The next question that arose was how was this inequality of 

 curvature produced ? This was explained to be due to the method, 

 employed by the Japanese for making the face of the mirrors 

 convex, which method had hitherto been quite unknown to 

 foreigners, but which Prof. Ayrton had, after much trouble, 

 found to consist in scratching the face while cold with a viegebo, 

 or "distorting rod." During the operation the mirrors became 

 visibly concave, but, receiving a "buckle," sprung back again 

 so as to become convex when the pressure of the rod was re- 

 removed. The thicker parts of these magic mirrors yielded less 

 under the pressure, were made therefore less concave when 

 under the rod, and sprung back less, or became less convex, 

 when the pressure of the rod had been removed. He then 

 showed how this explained the fact discovered by Prof. Atkin- 

 son, of the Imperial University, Japan, in 1877, that a small 

 scratch made on the back of a mirror with a blunt nail, although 

 producing apparently no effect on the other side, became never- 

 theless visible as a bright line on the screen when a light was 

 reflected from the mirror. 



Prof. Ayrton concluded by remarking that while the Japanese 

 knew nothing of the so-called magic phenomenon that formed 

 the subject of the paper that evening, he had ascertained that 



