Let It Shine: Making Fire from the Sun

http://www.motherearthnews.com/renewable-energy/making-fire-from-the-sun-zbcz1401.aspx

The following post summarizes the author’s selection from his book Let It Shine: The 6,000-Year Story of Solar Energy.

Burning Mirror Solar Concave Mirror

Like an “Indiana Jones” adventure, Chinese archaeologists have recently found the oldest solar device – a bronze concave mirror – capable of almost instantaneously making fire from sunlight. The discoverer called the 3,000-year-old apparatus “a world-class marvel…one of the great inventions of ancient Chinese history.”

Confucius wrote that the eldest son started the noon-day cooking fire by focusing the sun’s rays with such a concave mirror onto kindling. Around the 3rd century BCE, the Greeks independently developed concave mirrors. Both the Chinese and Greeks called them burning mirrors because they concentrate enough solar energy onto a combustible object to burst the object into flames. The Europeans, like the Chinese, used them to kindle wood for cooking.

When natural scientists of the Renaissance learned of these inventions, many envisioned using them as the ultimate weapon: engulfing in solar flames whole armies and ships. Roger Bacon, a thirteenth-century English scholar, believed that with twelve powerfully focused mirrors, Christendom could retake the Holy Land without shedding any Christen blood. Although never used for warfare, they had practical uses.

Practical Uses of Burning Mirrors

Florentine workmen soldered with burning mirrors. Burning mirrors also distilled perfumes. The sketch books of Leonardo da Vinci show that the great Italian hoped to realize his solar ambitions by the use of burning mirrors. He planned to build one with a radius of ½ a mile to heat water for processing wool, Florence’s principal industry, and for heating water for swimming pools.

When early scientists sought fame and glory through spectacle, powerful burning mirrors outclassed just about any other device, thrilling the public from London to Paris, who watched in awe the concentrated rays of the sun melt metals and vitrify glass in seconds.