Buying the Dark Lines of the Solar Spectrum: Joseph Von Fraunhofer’s Standard for the Manufacture of Optical Glass

Abstract

Fraunhofer's work on spectral lines was an outgrowth of manufacturing needs, not of theoretical investigations, as is commonly assumed. He was not trying to prove anything, but rather to find means of calibrating his lenses. That's why the British could not replicate his work based on theoretical knowledge alone. The spectral lines divided up the spectrum into standard regions and allowed F. to measure refractive indexes of his glass using monochromatic light.F. had to be clever and reveal enough of his secrets to convince people that he had the best techniques and lenses, but not enough to allow others to replicate his work. The idea of using the dark lines to test lenses spread rapidly throughout Europe, but the artisanal skills did not.