A Burning Lens older than Archimedes and newer than Solar Furnaces: Febo
"Have you ever seen this stone in the chemist's shops, the beautiful and transparent one, from which they kindle fire?"
"Do you mean the burning-glass?"
"I do. Come what would you say, pray, if I were to take this, when the clerk was entering the suit, and were to stand at a distance, in the direction of the sun, thus, and melt out the letters of my suit?"
"Cleverly done, by the Graces!"
Aristophanes - The Clouds - dialogue between Socrates and Strepsiades about burning glass.
Lenses have been used since the dawn of time to burn things and lit fires. Probably, in ancient times, we used vases filled with water as rays of sunlight catalyst, directing them to wood or straw. This was the beginning of a millenary history, when we controlled sun light in order to burn or... carve!
The first lens that we know of is the Assyrian Nimrud Lens, a round piece of glass from the eighth century BC found in Iraq. We can’t be sure that they used it as a burning glass, but there are some ancient Egyptian hieroglyphs depicting meniscus lenses. Since this first evidences, we started founding more mirrors or glasses used for different applications!
The dialogue above is an excerpt of Aristophanes' The Clouds, the first written evidence of burning lenses. It’s a comedy written in 423 BC in Athens, Greece, for the City Dionysia, a sort of ancient festival in honour of the god Dionysus.
Another Greek who probably used burning lenses is Archimedes. We know him for his mathematical and engineering discoveries and inventions and there's a myth about him using burning lenses to incinerate Roman boats during the siege of Syracuse, in 212 BC. Anyway, even if Archimedes probably didn't use them, he protected the walls with different amazing inventions you can find here. Unfortunately, Greeks are known for their love for wine and the Roman army entered the city while the guards were celebrating the goddess Artemis!
There are other famous evidences of lenses used to burn in ancient times, one of these is the treatise written around the sixth century by Anthemius of Tralles, the geometer and architect who designed Hagia Sophia, the world biggest church (then mosque) of the Middle Ages! Still in the sixth century, Proclus Oneirocrites studied the lenses after being impressed by the tales of Archimedes and purportedly helped to destroy the fleet of Vitalian during the 515 AC assault of Constantinople. As a matter of fact, it seems that the real treat Vitalian army had to face was a sulphur-based chemical close to Greek fire, and not the lens proposed by Anthemius, but the research upon lenses continued to improve...
Progress was on its way and burning lenses were not used for (supposed) military purposes after these two episodes! Science took advantage of the lenses’ capacity to concentrate heat in a single point and great scientists of the past made researches to improve the lens burning skills. Experiments started in 1774 by French scientist Antoine Laurent Lavoisier with burning lenses which brought to the discovery of oxygen, putting an end to the millenary beliefs of the 5 elements that compose the world: air, fire, water, earth, and ether. It was the beginning of modern chemistry, and all thanks to burning lenses!
The last kind of burning lenses of the past of which I would like to talk to you are still used today: the solar furnace. A solar furnace is a structure that concentrates solar energy, usually with directional mirrors, in a single place in order to reach high temperatures. These structures are based in sunny places around the world, such as the southern mountains of France, and sooner we'll probably see one in Uzbekistan, and they are mostly used for industrial purposes.
The energy of the sun is concentrated in a small area - usually smaller than a hob - and it can reach temperatures from 1.000 degrees Celsius (1.830 degrees Fahrenheit) up to 3.500 degrees Celsius (6.330 degrees Fahrenheit)! The biggest one is the Odeillo solar furnace, located at Font-Romeu-Odeillo-Via in the Pyrénées-Orientales and it was built during the 60’s. This solar furnace uses 9.600 mirrors reflecting the sunlight into a 40cm target, in the centre of the main tower. The heat reached is the equivalent of 10.000 suns and is used in aerospace and nuclear safety research! Another good purpose of this buildings is that they don’t pollute and don’t produce waste! Certainly a better use of these lenses than the bellicose ideas of ancient scientists!
Fifty years passed since the Odeillo solar furnace has been built and more than two millennia from Archimede’s burning mirrors, but what is the new frontier of burning glasses? We stopped using mirrors to burn people - and this is already good news - and we invented a way to use sun to create art!
Febo is the first solar pyrography tool capable to convey the sun energy to draw on supports such as wood, felt, and leather. It produces no waste and has a simple ambidextrous Italian design, with a protection while at rest, so you can’t burn your house unintentionally!
This little tool is the first pyrograph that does not need electricity or an already lit fire to work. Actually, it’s the first pyrograph that can light a fire when needed, using only a glass and the sunlight! At the very end of this long story of burning lenses we can finally create instead of destroy, with the use of this little, but powerful, tool!