Premier Zhou and the Transmitter of Western Han Dynasty
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Premier Zhou and the Translucent Mirror of the Western Han Dynasty There is a very special cultural relic in the bronze exhibition hall of the Shanghai Museum, the Mirror of Light Seeing the Sun in the Western Han Dynasty. The bronze mirror is 7.4 cm in diameter and weighs about 50 grams. The magic of this bronze mirror is that when a strong light or focus light shines on the mirror, it can reflect the pattern on the back of the mirror through the mirror and projected onto the wall. On the projection, the pattern on the back of the mirror, the hole on the base and even the inscription are clearly visible. On the back of it is the inscription of eight characters: the light of the sun, the world is bright, so this mirror is also called "the light of the sun" transparent mirror.
Many ancient books have recorded this kind of "translucent mirror". In the Book of Ancient Mirrors of the Tang Dynasty, it was said: "Cheng Rizhao recites his paintings and goes into the shadows without losing anything." The saying of "translucent light" was also spread from the Tang Dynasty. The ancients always regarded the bronze mirrors as "gods". But strangely, by the Song Dynasty, people had no idea of the principle of making the mirrors, and the method of making them was lost. Wuqiuyan in Yuan Dynasty, He Mengchun in Ming Dynasty and Zheng Fuguang in Qing Dynasty all described and explored the transparent mirror, but the specific principle of making it is still unclear.
One afternoon in the summer of 1969, a special guest, Premier Zhou Enlai, was welcomed to the old museum of Shanghai Museum (now Zhonghui Building). Mr. Ma Chengyuan, the former curator of the Shanghai Museum, recalled that we had brought out the most wonderful cultural relics for the Prime Minister to enjoy, including transparent mirrors. When introducing the transmitter to the Prime Minister, the Prime Minister felt that this phenomenon was very strange. He personally took the transmitter to the window and observed it repeatedly with sunlight. The Prime Minister also made various speculations about the principle of the transmitter. Finally, he said that you should do a good job in the future and make this clear.
So the research on the transmitter was officially launched. After several years of hard work, a group of scholars from Shanghai Museum and Shanghai Jiaotong University finally understood the principle of transparent mirror: the edge of the transparent mirror is wide and thick, the back of the mirror has protruding decorations and inscriptions, while the mirror body is very thin, about 1 mm, and the mirror surface is slightly upward protruding. In the casting process, the uneven thickness causes casting stress of the bronze mirror, and when grinding the mirror. Elastic deformation occurs, so the curvature of the thick part is small, and the curvature of the thin part is large. Because the difference is very small, only a few microns, the naked eye has no way to detect. The difference of curvature corresponds to decoration. When light illuminates the mirror, the reflected light scatters in the place with larger curvature, and the projection is darker. Where the curvature is smaller, the reflected light is concentrated and the projection is brighter. Therefore, we can see bright handwriting patterns in the reflection image. These are the images on the back of the mirror, and from the surface, it seems that the bronze mirror can really "translucent".