III. Burning Glasses and Moon Mirrors.

We read in the Chou-li that the officials in charge of light received the brilliant light ### from the sun with the Fu-sui, and the clear water from the moon with a mirror. ¹ (Le Tscheou-li par E. Biot Vol. II p. 381.) The commentators say that Fu-sui ### is equivalent to Yang-sui ### or ### a burning glass or a burning mirror.

Wang Ch`ung speaks of burning glasses in Vol. I, p. 378 and Vol. II, p. 351 where he informs us that they were made by liquefying five stones on the ping-wu day of the 5th moon. If this be true, the material must have been a sort of glass, for otherwise it could not possess the qualities of a burning glass. Just flint glass of which optical instruments are now made consists of five stony and earthy substances:---silica, lead oxide, potash, lime, and clay. The Taoists in their alchemistical researches may have discovered such a mixture.

Other authors maintain that the Yang-sui as well as the Fang-chu were both metal mirrors. The Pên-tsao-kang-mu describes the Yang-sui as follows: "It is a fire mirror made of cast copper. Its face is concave. Rubbing it warm and holding it towards the sun, one obtains fire by bringing some artemisia near it. This is what the Chou-li says about the comptroller of light receiving the brilliant light from the sun by his fire speculum." ²

According to the same authority the K`ao-kung-chi states that both mirrors are made of an alloy of copper and tin. Other writers describe this alloy as ### "gold and tin" or "bronze and tin." The fire mirror must be cast in the 5th month on a ping-wu day at noon, the moon mirror in the eleventh month on a jên-tse day at midnight.³ These times, the middle of summer and of winter are in harmony with the theory of the Five Elements.

The secondary names of the two mirrors show that they are looked upon as correlates and opposites, one connected with the Yang fluid or fire, the other with the Yin fluid or water. The Yang-sui ### is also called ###, and the Yin-sui (moon-mirror) ###.

It is possible that the ancient Chinese also knew burning glasses to to which Wang Ch`ung refers, as well as burning mirrors. Huai Nan Tse III, 2 r. mentions both burning glasses (mirrors) and moon mirrors. "When the burning glass sees the sun, it burns, and there is fire; and when the Fang-chu sees the moon, there is moisture and water." ⁴

We learn from the Liki (Legge, Sacred Books Vol. XXVII, p. 449) that in the Chou period the use of the fire mirror was quite common among the people, for among other articles a son serving his parents should hang on the left side of his girdle was the metal speculum for drawing fire from the sun, and on the right, the borer for obtaining fire from wood. ⁵ The commentator remarks that the son used his metal speculum to obtain fire when there was sunshine, and his borer when the sky was covered.

The Fang-chu ### attracting water from the moon is differently described by various authors quoted by the Pên-tsao-kang-mu under the head ###. One writer holds that it is a big oyster ### which, when rubbed and held up towards the moon, draws some drops of water from it, resembling dew in the morning. Another regards it as a stone, others as a mixture of five stones. We find also the explanation that ### means a stone ###, and ### a pearl ###. The Pên-tsao-kang-mu rejects all these explanations contending that the Fang-chu was a mirror like the burning speculum, and similarly manufactured. This view is supported by the above quoted passage of the Chou-li, which expressly speaks of a mirror employed to obtain water from the moon. This very pure water was perhaps used at sacrifices.

According to the Chinese theory the moon is water, consequently water can be drawn from it. As a matter of fact this is an illusion, and, if the Chinese have discovered some drops upon their moon-mirrors, they were probably dew drops.

Burning reflectors were known to the Greeks. Euclid about 300 B.C. mentions them in his works, and Archimedes is believed to have burned the Roman fleet at Syracuse in 214 B.C. with these reflectors, probably a myth. Plutarchus in his life of Numa relates that the Vestals used to light the sacred fire with a burning speculum. As the Chou-li dates from the 11th century B.C. it is not unlikely that the Chinese invented the burning reflector independently and knew it long before the Greeks.