METAL INDUSTRY. 447 



representing mythological persons, birds, flowers, weapons and 

 pithy expressions. This is done after the front of the casting has 

 been pohshed off till from 0*5 to 2-5 millimeters thick, and finally 

 coated with an amalgam which is composed of from one to two 

 parts tin, and one part of quicksilver. These metal mirrors are 

 generally circular in form with a diameter of 15-5 to 16 centimeters. 

 There is at one side a staff-shaped handle, with which they are 

 held. 



It was known to the Chinese many centuries ago, that some of 

 these mirrors when they reflected the sunlight on the wall, mirrored 

 at the same time the raised figures on their backs, more or less 

 distinctly. 



These mirrors are found also in Japan. The property mentioned 

 was long ago discovered accidentally by Japanese ladies, as 

 Muraoka ^ has pointed out. Atkinson,^ however, was the first to 

 call general attention to this phenomenon, while Brewster ^ pub- 

 lished a work on the magic mirrors of China in 1883. In modern 

 times these mirrors have been investigated by several physicists. 

 We are indebted especially to the larger works of Ayrton and 

 Perry ,'^ Govi,^ and Bertin,'^ all of whom agree in the explanation of 

 the phenomena. 



It was thought formerly that the pictures and decorations at the 

 back of the mirror plate were inlaid with some other metal, or that 

 by beating the mirror with a hammer at these figured places a 

 greater density was produced, or the pecuHar property was at- 

 tributed to the composition of the alloy itself All these explana- 

 tions have proved false on closer investigation. The analyses show 

 that the mirror bronzes have often a very different composition, as 

 is seen in table C. 



The Italian Govi has pointed out convincingly that the peculiar 

 property of the magic mirror proceeds from the polishing, and is 

 accidental, but can be easily produced. It is due to the uneven- 

 ness in the convex arching which the reflecting surface receives in 

 polishing, in consequence of the uneven pressure from the back, 

 and is entirely independent of the chemical composition. Later 

 on Muraoka and others proved experimentally that mirrors can 

 be made not only of bronze and brass, but also of simple metals 

 which will exhibit these magic properties in like manner. They 

 are shown even more beautifully than in the sunlight, when a 



^ " Erklarung der magischen Eigenschaften des japanischen Bronzespiegels 

 und seiner Herstellung." " Mittheil. der deutsch. Gesellsch. Ostasiens," Heft 

 31, 1884. 



2 Nature, vol. xvi. 1877, p. 62. 



3 Philosophical Magazine, vol. 1. 



■* " On the Magic Mirrors of Japan." " Proc. Roy. Soc." xxviii. pp. 127-142. 



^ " Les Miroirs magiques des Chinois." "Ann. de Chim. et de Phys." 5 Serie. 

 T. XX. 1880, pp. 99-110. 



^ " Etude sur les Miroirs magiques." " Ann. de Chim. et de Phys." 5 Se'rie. 

 T. xxii. 1881, pp. 472-513. 



