of Light Radiations emitted by Iron Vapour. 11 



Explanation of Plate I. figs. 1 8f 2 (enlarged 5 times). — The 

 spectrograms were obtained by means of burner No. 2. The 

 appearance of the flame and cones, as seen in the direction 

 of the collimator axis, is shown in fig. 5. The two cones are 



Fig 5. 



2 nd Cone. 



Position of 5//£ \yVv!/ — 



Burner 



Method of observing spectrum of air-coal gas name 

 with burner No. 2. 



completely enveloped by the flame. An image was formed 

 on the slit in such a way that the latter passed across the 

 cones at a point situated about two-thirds up from the base. 

 It will be seen that with this arrangement the resulting 

 photograph shows two spectra due to the cones, which are, 

 as it were, imbedded in the spectrum of the flame. On the 

 two cone spectra there are superimposed spectra, due to those 

 parts of the flame, situated immediately in front and behind 

 the cones. This is, of course, unavoidable, but must be 

 borne in mind when interpreting the photograph. 



The spectrograms obtained in this way show in a most 

 striking manner the relative sensitiveness of the various 

 vibrations to the chemical and thermal forces which prevail 

 in the cone and flame respectively. 



The flame lines appear as long lines passing right through 

 the spectra of the cones and beyond — for example, the lines 

 3860, 3920, and 4376. It will be noticed that over the cone 

 spectra they seem slightly enhanced. This may be due 

 either to a real enhancement by chemical action, or to the 

 superposition of the two emissions from the cone and the 

 portions of the flame in front and behind^ as already 

 referred to. 



The most remarkable feature of those cone lines which 



