The Principles of Spectrum Analysis. 363 



" 4. Bright lines produced by coloured flames, or by the introduc- 

 tion of different substances into flame. 



" The following clironological table contains the names of those 

 who have made the principal steps in these different subjects : — 



"Newton 1701 



Wollaston 1802 



Fraunhofer 1815 



Cosmical. Absorption Sands. 



Brewster, 1832. Brewster, 1832. 



E. Becquerel, 1842. W. H. Miller ) lg33 



Draper, 1842. and Daniell, j 



Stokes, 1852. W. A. Mfller, 1845. 

 Brewster and ) -, ocr . 

 (Gladstone, ) 



Electric Light. Coloured Flames. 



Wheatstone, 1835. Brewster, 1822. 



Boucault, 1849. Herschel, 1822. 



Masson, 1851—55. Fox Talbot, 1826, 1833, 



Angstrom, 1853. 1834. 



Alter, 1854—55. W. A. Miller, 1845. 



Secchi, 1855. Swan, 1857. 



Pliicker, 1858—59. 

 Y. Willigen, 1859. 



Kirchoff 1859. 



Kirchhoff and Bunsen 1860." 



In order to a right understanding of the results which have 

 been reached by the recent labours of Kirchhoff and Bunsen, it 

 is necessary to be acquainted with the nature of the dark lines, 

 which are so many touchstones or tests by which they have 

 worked them out. Let us suppose a prism of blue glass to be 

 used for effecting the decomposition of a ray of solar light. 

 We have an elongated image, not, however, containing seven 

 colours, as when a white prism is used. The yellow, blue, and 

 green are all absorbed, and we have only the two extreme 

 colours, violet and red, the latter also diminished in breadth, 

 A comparison with the normal spectrum will make the differ- 

 ence at once clear. In passing through our atmosphere, or 

 the atmosphere of the sun, similar changes may take place, 

 and thus materially assist in producing these dark lines. More- 

 over, there are a class of rays in the solar spectrum which our 

 eyes cannot see, and of which we can only judge by their effects. 

 Of such are the chemical rays which manifest their action in 

 the beautiful results of the photographic art. We may instance 

 also another set found beyond the violet rays, whose presence 

 has been demonstrated by Professor Stokes, by transmitting 

 them through a solution of sulphate of quinine. They have a 

 light bluish-lavender colour. Thus, it will seem that certain 



