THE SUN. 51 



celebrity if it had appeared in French, English, 

 or German, instead of Swedish." 



It was not until 1859 that the principles of 

 spectrum analysis were fully enunciated by 

 Gustav Robert Kirchhoff (1824-1887), and his 

 colleague in the University of Heidelberg, Robert 

 Wilhelm Bunsen (1811-1899). Kirchhoff demon- 

 strated that a luminous solid or liquid gives a 

 continuous spectrum, and a gaseous substance a 

 spectrum of bright lines. In the words of Miss 

 Clerke, " Substances of every kind are opaque 

 to the precise rays which they emit at the 

 same temperature. That is to say, they stop 

 the kinds of light or heat which they are then 

 actually in a condition to radiate. . . . This 

 principle is fundamental to solar chemistry. It 

 gives the key to the hieroglyphics of the Fraun- 

 hofer lines. The identical characters which are 

 written bright in terrestrial spectra are written 

 dark in the unrolled sheaf of sun-rays." Kirch - 

 hoff made several determinations of the sub- 

 stances in the Sun, proving the existence of 

 sodium, iron, calcium, magnesium, nickel, barium, 

 copper, and zinc. His great map of the solar 

 spectrum was published by the Berlin Academy 

 in 1860, and represented an enormous amount 

 of labour. It was succeeded by another map 

 by Angstrom, published in 1868. But both of 



