Fraunhofer's solar spectrum
Then,
Joseph Fraunhofer
(1817) while working at a military and surveying
instruments firm rediscovered the lines while calibrating the optical properties
of glasses. He discounted Wollaston's colour boundary interpretation, he
observed a continuous color change across the spectrum; no color
discontinuities occurred at the dark lines.
He later discovered dark lines in the spectra of stars and noted that some of
the lines in stars were absent in the sun and vice versa. This clearly indicated
that not all of the lines were of terrestrial origin. To his credit he did not
taint his findings with deductive interpretations and confined himself to highly
accurate empirical observations. Herschel considered that
the Fraunhofer lines could either be caused by absorption in a cool gas in the
earth's or in the sun's atmosphere.
Sir David Brewster (1836) found that certain lines had strengths that varied with the sun's elevation and with the seasons. He correctly ascribed these 'atmospheric lines' as originating in the terrestrial atmosphere. Remarkably, he failed to take into account Fraunhofer's observational evidence for the stellar origin of certain solar absorption lines. Ignoring crucial astronomical data tends to isolate a researcher from the truth to a certain degree.
Later, the solar origin of most of the Fraunhofer lines were established beyond a shadow of a doubt by Bunsen and Kirchoff. Shortly after, Brewster (1860) compounded his previous blunder and insisted that the whole issue should still be considered undecided. It seems that in the face of such strong belief no amount of evidence can sway the die-hard. Belief is stronger than reason.
