Optics in the 19th Century
Before the 1800's little was known about the behavior of light in optical
instruments. In 1666 Newton noted that white sunlight sent through a prism
produced a rainbow of color. In 1802 the English physicist William Wollaston
found that if he placed a thin slit in front of a prism the spectrum displayed
a series of parallel dark lines. But he did not continue his experiments.
Optics in the early nineteenth century was a growing industry. Napoleon
Bonaparte's passion for spyglasses had set surveyors and generals to order
portable telescopes and the research of Herschel who charted the southern
skies from an observatory at the Cape of Good Hope, had inspired interest in
large telescopes. The new breed of artisans emerged -- the opticians. One such
was Jesse Ramsden (left) of London, who was such a perfectionist that he persevered
at all costs until he got it right. An eight foot altitude measuring circle he
built for the Dunsick Observatory in Dublin was a masterpiece but it was
delivered 23 years after its contracted deadline. Equally late to his social
functions, apparently he arrived for a party at Buckingham Palace at the hour
and day specified but one year too late!
Another of renown was Alvan Clark
(and son on the right), an American telescope maker, who
prospered as a portrait painter before he switched careers and built what are
still regarded as the finest refracting telescopes in the world. Clark was
said to be able to fire 6 rifle bullets through a distant board with such
accuracy that it looked like a single shot had been fired. His vision was so
keen that he could spot tiny bubbles and ripples in glass that were invisible
to most.
Josef von Fraunhofer
(left) was another. He was born in Munich in 1787 and was the
orphaned 11th son of a poor master glazier . He was then apprenticed to
Philipp Weichselberger, a dull-witted Munich glasscutter who kept him
overworked, underpaid, underfed and uneducated. This was until July 21, 1801,
when the rundown building that was Weichselberger's house and shop collapsed
and Fraunhofer was the only survivor, pulled many hours later from its ruins.
His rescue made the headlines and his plight attracted the attention of
Maximilian Joseph, the elector of Bavaria, who visited the injured boy in the
hospital and was impressed by his intelligence and good humor. The elector
gave Fraunhofer 18 ducats, which was enough to buy a glass-working machine,
books, and release him from the remainder of his apprenticeship. This was
enough to launch his career, and he became one of the best known maker of
telescope lenses.
Fraunhofer
(right) started out using spectral lines as sources of monochromatic
light for his experiments in improving the color correction of his lenses, but
soon became fascinated by the lines themselves. He mapped hundreds of lines in
the spectrum of the sun and found identical patterns in the spectra of the
moon and planets -- of course because these bodies reflect sunlight. When he
turned his telescope on other stars, their spectral lines looked different.
This remained a mystery to him and he died in 1826 of tuberculosis at age 39.
Today we know these lines as emission and absorption lines that are used in
spectroscopy as sources of information on the temperatures, compositions and
motions of gaseous nebulae and stars.
Later, between 1855 and 1863, Robert Bunsen (the inventor of the Bunsen
Burner!) found that the distinct sequences of Fraunhofer lines were produced
by chemical elements.
Robert Bunsen
(left) was born in Germany in 1811. His father was a librarian and
professor of linguistics in Gottingen and Robert studied chemistry there
before travelling and studying in Paris, Berlin and Vienna. He became
professor at Heidelberg in 1852 and remained there until his retirement, 10
years before his death in 1899. He was a great teacher and his lecture courses
were famous. He continued to research until he was 80. He admitted that he
never found time to marry. Actually a better reason may be that he smelled
terrible because of all the chemicals that he was working with. Emil Fischer's
wife said of him: "First I would like to wash Bunsen and then I would like to
kiss him because he is such a charming man."
Bunsen was an experimenter and not a theorist. He devoted much of his
career to chemistry and organic and inorganic compounds. During this work he
lost the sight of an eye and nearly died of arsenic poisoning. This convinced
him to abandon that research.
With his fellow professor Kirchhoff he then moved on to spectroscopy. One
evening they saw from the window of their lab in Heidelberg a fire raging in
the port city of Mannheim 15 km to the west. Using their spectroscope, they
detected the lines of barium and strontium in the flames. This set Bunsen to
wondering whether they might be able to detect chemical elements in the
spectrum of the sun. They were successful and by 1861 had discovered the
elements sodium, calcium, magnesium, iron, chromium, nickel, barium, copper
and zinc in the sun.
Bunsen later went on to build a Bunsen cell, a zinc-carbon primary cell
which he used to obtain metals by electrodepositing from solution. He was a
master of gas analysis, using it in his study of Icelandic volcanoes and
English blast-furnaces. He was a pioneer in photochemistry and for this built
a photometer. And he was a master builder of lab devices -- the filter pump
and the famous Bunsen gas burner, based on a model by Faraday and later sold
by his technician Peter Desdega.
