48 M. A. Wullner on the Absorption of Light. 



On this scale the Fraunhofer's lines 



C lay between the divisions 67 and 68, 

 D „ „ 86 „ 87. 



The dark lines of the absorption spectrum were upon and 

 between the divisions 



72 90—91 



73—74 92—93 



75—76 94—95 



77—78 96 



79—80 98 



81 100 Limit of the green ; the follow- 



83 101 — 102 ing dark lines are no longer 



85 103 — 1 04 visible with a certain thickness 



86—87 Fraunh. D 105—106 of iodine vapour. 



88—89 107—108 



109—110 



In order to compare now the spectrum of the iodine flame with 

 the absorption spectrum, I proceeded essentially as in the pre- 

 vious case : the hydrogen flame loaded with incandescent iodine 

 vapour was brought in front of the slit of the spectrum appa- 

 ratus. To protect the apparatus from the action of iodine 

 vapours, and to ensure the regular combustion of the flame, it 

 was surrounded by a cylindrical lamp-glass. 



The hydrogen flame, in which there is not much iodine vapour, 

 is only feebly luminous, and that with a green light ; it is more 

 luminous, and that with reddish-yellow light surrounded by a 

 feebly luminous border, if the hydrogen gas is strongly charged 

 with iodine vapour so that a strong current of red vapours issues 

 from the flame. 



If care is taken that the brightest part of the flame is in front 

 of the slit of the spectrum apparatus, a glance into the telescope 

 is sufficient to show the surprising similarity between the cha- 

 racter of the flame spectrum and of that produced by daylight 

 passed through iodine vapour. 



From about the place corresponding to Fraunhofer's line C, 

 the flame spectrum, like the absorption spectrum, appears com- 

 posed of alternating bright and dark lines arranged like a barred 

 grating, most perceptibly till the beginning of the green. 



The green appeared much more continuous; the dark bands in 

 it could scarcely be distinguished. The latter were much more 

 distinctly seen if the flame, with a smaller quantity of iodine, was 

 feebler, and, as before said, had a greenish light ; the agreement 

 in the character also of this part of both spectra was then very 



