CHAPTEE VI. 



KIRCHHOFF'S MAP AND WORK. 



IN the course of the last chapter, we found ourselves, as a 

 result of all the work done up to 1860, face to face with the 

 statement that the atmosphere of the sun contained, if it was 

 not entirely built up of, substances known to terrestrial che- 

 mistry ; and further, that our knowledge, of which this was only 

 the first foretaste, might be almost indefinitely extended by a 

 minute study of the Fraunhofer lines in connection with the 

 spectra of terrestrial elements. 



To this work Kirchhoff now set himself with tremendous 

 vigour, and in the years 1861 and 1862 communicated memoirs 

 of priceless value to the Berlin Academy. 1 



All the time the early work described in the previous chapters 

 was being carried on, the apparatus employed was undergoing a 

 sort of evolution, while various new methods were being de- 

 veloped. The various parts of the spectroscope were being per- 

 fected and made more compact ; glass got better ; better surfaces 

 were given to prisms ; until in KirchhofFs time it attained the 

 dignity of a complete and distinct instrument. We may now 

 then lay aside the provisional arrangement described in Chapter 

 IV. to make ourselves thoroughly acquainted with the con- 

 struction of the actual instrument, and its recent additions and 



1 Researches on the Solar Spectrum and the Spectra of the Chemical Elements, 

 by G. Kirchhoff, Professor of Physics in the University of Heidelberg. A trans- 

 lation by Roscoe was published by Macmillan. 



