210 



From Newton to Kirchoff. 



solar line held a position in the spectrum identical with 

 that of the yellow lines of sodium, and much later, Ang- 

 strom had, by a long and careful examination of the subject, 

 enabled himself to say : " I am convinced that the explana- 

 tion of the dark lines of the solar spectrum embraces that 

 of the luminous lines of the electric spectrum." Little, 

 however, did Fraunhofer or Angstrom suspect what was so 

 soon to be proved, that the noticed coincidence in position 

 of the solar and sodium lines was the key to the mystery 

 which perplexed them. Not only was the book of solar 

 and stellar chemistry unclasped, but the key to the trans- 

 lation of the characters in which it was written was already 

 in the hands of those who yet continued to search for it 

 with so much patience and solicitude. 



Such was the condition of the subject as late as the year 

 1859. It was in that year that Bunsen and Kirchoff made 

 their most memorable discoveries. By skillfully combing 

 the results of previous discoveries with their own masterly 

 experiments, they were able to interpret Fraunhofer's capi- 

 tal observation of the coincidence of solar and metallic 

 spectra, and to announce the principle which reduces both 

 sets of phenomena to a single and perfect system. It had 

 been already found that each terrestrial element always gives 

 lines having the same position. Kirchoff verified the fact 

 that the positions of these terrestrial lines, and certain 

 solar lines were exactly coincident. If it could be after- 

 ward shown that bright lines could be changed into dark 

 ones, it would then appear that the solar lines and the coin- 

 cident bright lines are due to the same cause. To Bunsen 

 and Kirchoff belongs the supreme honor of discovering 

 the method by which the beautiful colors of terrestrial 

 lines may be changed to darkness under the immediate eye 

 of the observer. Let Kirchoff himself tell us the story of 

 this splendid achievement: a In order to test by direct 

 experiment the truth of the frequently asserted fact of the 



