284 Spectra of Carbon, Titanium, and Vanadium. 



current, the electric field will, already at the lower tempera- 

 tures, be of sufficient strength to give rise to traces of the 

 electrically controlled emission. Now, since this emission 

 naturally develops progressively, as the temperature and 

 consequently also the electric field increase, the erroneous 

 impression will be created that the observed spectrum (which 

 is of course composed of the electrically controlled emission 

 and that due to thermo-chemical excitation) is entirely 

 governed by the furnace temperature. 



It seems to me therefore highly probable that the electric 

 tube resistance furnace, and in particular the special furnace 

 arrangement used by Dr. King, is most unsuited to investi- 

 gations having for object the study of the effect of tempera- 

 ture upon the spectrum lines of an element, because it is not 

 possible with such furnaces to discriminate readily between 

 the lines controlled by temperature and those, the emission 

 of which depends upon electric actions* Hence, spectrum 

 tables which are founded solely on furnace observations and 

 purpose to give the variation of the spectrum with tempera- 

 ture, are necessarily misleading, since in their compilation 

 no account has been taken of the composite character of the 

 spectrum observed. One of the objects of experimental 

 spectroscopy is to break up a complicated spectrum and to 

 trace the origin of the various component parts, in order 

 to pave the way for the search of still closer relationships 

 between the various lines or groups of lines. This can often 

 only be accomplished by lengthy comparative investigations 

 under most diverse conditions. In this way I have shown, 

 that the particular furnace emission of iron vapour which is 

 controlled by temperature, is obtained by itself in the mantles 

 of flames, where it can be observed to much better advantage 

 than in the tube-furnace. 



Hence it seems to me that the study of furnace spectra 

 can only lead to trustworthy and useful results, if it be sup- 

 plemented by an examination of both arc and flame spectra 

 of the same element, the whole investigation being of course 

 made, as far as possible, with the same spectrographs 

 applicances. 



Manchester, July 1919. 



Note added November 21. 



The hazy red bands of the fringe are due to the oxide and 

 more especially the carbide of calcium. The oxides of 

 strontium and barium when added to the carborundum, with 



