222 Mr. G. A. Hemsalech : A Comparative Study 



must be the same as in flames. Also the close agreement 

 between the progressive development of the iron spectrum 

 with the rise in temperature, both in furnace and in flames, 

 testifies to the accuracy of Dr. Bauer's figures concerning 

 the temperatures of the flames involved. 



It should be possible with the help of the results here 

 given for iron to estimate the temperature of a source of 

 light in which thermo-chemical excitation prevails. Thus 

 we may conclude that the temperature of an air flame 

 burning in coal gas is about 1500° C. 



§ 7. Note on the Spectrum of Iron as excited by 

 Chemical Actions. 



Whereas complete similarity has been found to exist 

 between the spectra of iron as given by the mantles of 

 various flames and those observed in the furnace up to a 

 temperature of about 2400° C, no spectrum has been met 

 with in the furnace corresponding to that given by chemical 

 excitation in the air-coal gas cone. To judge by the deve- 

 lopment of this spectrum as regards mere number of lines, it 

 seems to occupy a position intermediate between that of the 

 oxy-acetylene flame and that of the self-induction spark, as 

 is shown by the following figures derived from observations 

 that were all made with the same spectrograph and therefore 

 bear comparison : — 



Mode of Excitation. Number of Lines. 



Thermo-chemical 100 



Chemical 220 



Electrical 440 



The origin of the cone emission has already been fully 

 discussed in a previous communication. 



§ 8. Additions and corrections to the Line Groups of 

 Class I. 



In the course of a previous research on flame spectra 

 attention was directed to the existence, in the several classes 

 of iron lines, of curious groupings of apparently related 

 lines. In particular, among the lines of class I. several 

 quartet groups were found in all of which the lines converge 

 towards the red. The present experiments with the furnace, 



