The ancient Chinese got fire in several stages : preservation of natural fire , getting fire by friction , gathering fire by drilling wood , and getting fire by a solar flint . The stage of getting fire by a solar flint began in the Bronze Age . There were two methods : One method was to use a metal cup with a pointed bottom . Put some moxa velvet on the bottom of the cup . The sunlight focused on the bottom . After some time the moxa velvet would be ignited . The other method was getting fire by using a concave copper mirror . In the “Annotations to Ancient and Contemporary Classics .” Cui Bao stated : “The solar flint is a mirror made chiefly of copper . When it is faced to an object it reflects an inverted image . When it is faced to the sun , it generates fire lit by a moxa cone .”
It proves that the “solar flint” was an ancient Chinese invention . The invention utilized the sunlight focusing property of the concave copper mirror to get fire from the sun . It is based on the principle of transformation of light energy into heat energy , and involves a deep knowledge of the light focusing property and the ignition points of the materials . This invention implied that the Chinese reached a stage of getting and using fire very freely .
Furthermore , the book “Polytechnic of Huainan” written in the second century . B.C . recorded : “Cut ice into a round object and face it to the sun . Put moxa in its shadow . Fire is generated .” Here , the shadow is meant the focus . The ancient Chinese used two incompatible things to generate fire , displaying a high ingenuity .
