In October 1859, German physicist Gustav Kirchhoff announced the results of his investigations with chemist Robert Bunsen on the dark lines that interrupt the otherwise continuous solar spectrum (1). These lines had puzzled practitioners and theorists alike since they were first observed in 1814 by German optician Josef von Fraunhofer (2).
Now it seemed that Bunsen and Kirchhoff had finally confirmed what others had long suspected, namely, that an individual metal produces its own characteristic pattern of bright spectral lines when it is burned. Furthermore, Kirchhoff asserted that Fraunhofer's lines "exist in consequence of the presence, in the incandescent atmosphere of the sun, of those substances which in the spectrum of a flame produce bright lines at the same place."
News of his claim spread quickly throughout the scientific world. In England, Bunsen's former student, Henry Enfield Roscoe, wrote to the secretary of the Royal Society, George Stokes (3): "Have you seen in the last no.
of the Annales ... a short note about Kirchoff's [sic] discovery...?"
Soon, Roscoe was offering public lectures on the subject to interested scientists and laymen alike. After one such presentation to the Chemical Society, moderator Warren De La Rue remarked (4)
[I]f we were to go to the sun, and to bring away some portions of it and analyze them in our laboratories, we could not examine them more accurately than we can by this new mode of spectrum analysis....
What really excited De La Rue, a stationer known for his photographs of the sun and moon, was the potential this method of analysis portended for astronomy. After all, French philosopher Auguste Comte in 1835 had clearly defined the domain of questions considered legitimate for Earth-bound observers to ask about the denizens of the celestial realm. "We can imagine the possibility of determining the...