Science: Big Burning Glass

In the ancient, half-ruined village of Mont Louis in the French Pyrenees, a great, flat mirror, nearly 40 ft. on a side, stares all day at the sun, turning automatically. Facing it is a parabolic mirror almost as big, into which the flat mirror throws reflected sunlight. The combination acts as a gigantic burning glass which can melt 130 Ibs. of iron in an hour. The fierce spot of concentrated sunlight can bore holes through aluminum oxide (the material used to line electric furnaces).

The big burning glass is not a new idea. The pioneer French chemist Lavoisier built one almost 200 years ago and succeeded in melting iron with the sun’s rays. The one at Mont Louis, by far the biggest ever built, has reached a temperature of 2,500° C. (4,500° F.). Electric furnaces can also reach high temperatures, but experiments conducted in them are complicated by carbon from the electrodes. The sun’s concentrated rays are pure heat; they can melt or vaporize a substance without contaminating it.

Designer Felix Trombe has a long list of experiments that he intends to perform with his pure heat. Most urgent: making hard-to-melt ceramics out of zirconium, thorium and aluminum oxides.