Joseph von Fraunhofer was certainly the most talented lenscrafter of his time. Though he received very little in the way of formal schooling, he dedicatedhis life to creating optical instruments of unsurpassed quality. Through hisefforts, telescopes and prisms of amazing clarity were created; in addition,he invented the device known as the spectroscope for observing the dark lines found in the visible spectrum, effectively founding the science of spectroscopy.
Fraunhofer was born in Bavaria in 1787. His father was a poor glass maker whocould not afford to send his youngest to more than a few years of school, and so at the age of 10 Joseph began working in the family workshop. Upon his father's death in 1789 Fraunhofer became an apprentice to a Munich lensmaker.Although young Fraunhofer showed much promise, the master lensmaker used himprimarily as slave labor, driving the boy to near-starvation and exhaustion.
Strangely, the luckiest day of Fraunhofer's life may have been July 21, 1801,when the run-down building in which he slept collapsed. Though unhurt, Fraunhofer was trapped beneath the wreckage, prompting a large community rescue operation; in fact, the Elector of Bavaria himself was drawn to the scene. Whenextricated, Fraunhofer was given a monetary award from the Elector--enough money to buy out the remainder of his miserable apprenticeship and to begin his own business.
Although he squandered much of his award on an unproductive get-rich-quick scheme, Fraunhofer retained enough money to remain in Munich, and in 1806 he was employed by the famous Munich Philosophical Instrument Company, one of themost prominent suppliers of scientific optical equipment in the world. Therehe was able to exercise his glassworking abilities, producing lenses and prisms of unprecedented clarity. He rapidly gained a reputation for constructinglens systems free of color flaws (such lenses were vitally important to astronomical observing). He also constructed, in 1817, a 9.5 inch lens for the Russian Dorpat Observatory; using this lens, Russian astronomers were able to discern over 2000 new double stars.
It was while he was perfecting his lenses that Fraunhofer made what was to behis most important discovery. In order to calibrate his instruments he wouldfocus them upon a bright candle. One day, however, he chose to use the lightfrom the sun. He was quite surprised to find a number of dark lines crossingthe sun's rainbow spectrum--lines that were not present in the spectra of candlelight. Although a few dark lines had been identified years earlier by William Hyde Wollaston (1766-1828), Fraunhofer's precise equipment enabled him to discern 574 individual lines in the spectrum of the sun.
Fraunhofer began to examine the spectra of many light sources using an invention called a spectroscope. He found that different elements, when heated to incandescence, would produce lines at different positions in the spectrum. Healso discovered that the light from the moon and the planets displayed the same line pattern as the sun, while other bright stars possessed individual spectral "signatures" (this is actually a logical conclusion, since the light from these bodies is simply reflected sunlight, but other stars generate theirown light). Working tirelessly, Fraunhofer succeeded in mapping the more thanfive hundred lines in the solar spectrum and calculating the approximate wavelengths at which they occurred.
These dark lines--now known as Fraunhofer lines--were actually areas of the spectrum where light is absorbed. When the light from a star encountersthe elements at the outside of its atmosphere, the elements will absorb certain frequencies. By observing any star's Fraunhofer lines, an astronomer canidentify the elements in that star's atmosphere. All of this was unknown to Fraunhofer himself, and was left for Gustav Kirchhoff (1824-1887) to explain in 1859.
While conducting his research on spectral lines, Fraunhofer had been using prisms to separate light into its component colors. However, it was also commonpractice to obtain a spectrum by passing the light through a very thin slit.It occurred to Fraunhofer that a wire mesh could be assembled wherein the holes would act as hundreds of extremely thin slits, effectively splitting andre-splitting the passing light. Thus in 1821 he constructed a diffraction grating comprised of 260 wires, producing a widely dispersed spectrum. He laterfound that an even wider (and more easily examined) dispersion could be obtained if the wires were set closer together.
Fraunhofer considered his methods trade secrets and never published them; therefore, much of his work was a mystery to his peers. Also, though he was a highly skilled craftsman, he was viewed by the scientific community as nothingmore than a technician. He was never truly accepted by the intelligentsia, and while he could attend scientific meetings he was never allowed to address them. He died of tuberculosis a few months before his 40th birthday.
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