Joseph von Fraunhofer

“Fraunhofer discovered that the apparent continuity of a rainbow is an illusion. There are tiny gaps, dim or black arcs of missing colors, too narrow for us to see in the glare of natural rainbows. To say it another way, there are specific colors (specific wavelengths of light) in which sunlight is deficient. Fraunhofer eventually catalogued 576 of these gaps, or "absorption lines": 576 specific wavelengths missing from sunlight. Fraunhofer's career of discovery was cut short by consumption.”

“By his invention of new and improved methods, machinery, and measuring instruments for grinding and polishing lenses, by his having the superintendence, after 1811, also of the work in glass-melting, enabling him to produce flint and crown glass in larger pieces, free of veins, but especially by his discovery of a method of computing accurately the forms of lenses, he has led practical optics into entirely new paths, and has raised the achromatic telescope to, until then, undreamed of perfection.”

“Fraunhofer's secrets of manufacture accompanied him to the grave. His artisanal knowledge was such that, after his death, even the apprentices who worked with him, in the same glass hut and with the same equipment, achieved only limited success in the manufacture of optical glass.”

“Fraunhofer had busied himself with glass his entire life. Working with glass was his family tradition, and the manufacture of optical lenses and prisms was his life.”

“Fraunhofer made a great many experiments connected with these mysterious lines, anxious to discover, if possible, their meaning, For although he now saw the lines, which had scarcely so much as been seen before, he could not understand them; he could not read what they said. They spoke to him, indeed, about the Sun, but they spoke in a foreign language, the key to which he did not possess.”

“With patience he went into the question, using the telescope as well as a very narrow slit... Close examination was rewarded by the making out of lines upon lines; till in the year 1814, that which witnessed the downfall of Napoleon and his banishment to Elba, Fraunhofer had mapped three or four hundred.”

“He must have been working quietly at the problem through years of European war and tumult. Crowned heads rose and fell; and nations changed hands; and tyrants were cast down; and brave men died by thousands for their countries; whilst Fraunhofer, in the midst of national seethings, calmly investigated the nature of black lines in sunlight.”

“He was the first to observe spectra due to gratings, and with them he made the earliest determination of wave-lengths.”

“I wished to find out whether a similar bright line could be seen in the spectrum of sunlight as in the spectrum of lamplight, and I found, with the telescope, instead of this, an almost countless number of strong and feeble vertical lines which, however, were darker than the other parts of the spectrum, some appearing to be almost perfectly black.”

“It will reward enough for me if, by the publication of the present experiment, I have directed the attention of investigators to this subject, which still promises much for physicial optics and appears to open a new field.”

“The number of different optical phenomena has become in our time so great that caution must be taken so as to avoid being deceived, and also to refer the phenomena to the simple laws.”

“Up to the present time, in experiments on diffraction there has been no instrument, except a magnifying-glass, which could be used with profit; and this may perhaps be one of the reasons why in this field of physical optics we are so backward, and why we know so little of the laws of this modification of light.”

“In all my experiments I could, owing to lack of time, pay attention to only those matters which appeared to have a bearing upon practical optics. I could either not touch other questions, or at most not follow them very far. Since the path thus traced in optical experiments seems to promise to lead to interesting results, it is greatly to be desired that skilled investigators should devote attention to it.”

“Since the violet rays through the objective of the theodolite telescope have a shorter focal length than the red rays, it is evident why the eye-piece must be displaced in order to see plainly the lines in the different colors.”