Iron Vapour in Air-Coal Gas Flame. 225 



influence on the metal vapour passing through it. In fact, 

 to judge by the luminosity of the vapour and that of its 

 spectrum, it seems that the region of maximum temperature 

 is that immediately surrounding the cone. In this region 

 nearly all the lines given by this flame, which comprise 

 those of Classes I. and II. only, appear brightest, but their 

 relative intensities are the same as in the flame above and, 

 indeed, the same as in the mantles of the oxy-coal gas 

 and oxy-hydrogen flames. After the vapour has passed 

 through this region there is a rapid, though not abrupt, 

 falling-off in the intensities of all the lines. It is possible 

 that this rapid diminution of the intensities is due to the 

 relatively small quantity of oxygen that remains over for 

 completing the oxidation of the hydrogen, the greater 

 portion of the former having already been consumed in the 

 vicinity of the cone ; the temperature of this flame would 

 therefore decrease very rapidly on passing into the region 

 above the cone. A very curious exception to the behaviour 

 of the majority of lines is disclosed by the quartet group y 

 (head line at 4376), which is apparently not in the least 

 affected by the change on passing from the cone to the 

 flame above. 



With regard to the oxy-hydrogen flame, its cone is very 

 short and sharply defined, but no enhancement of any line 

 whatever has been observed in it. All the lines reach a 

 maximum of intensity a little distance above the cone, after 

 which the vibrations die out gradually, as in the case of the 

 oxy-coal gas flame. The spectrum given by iron in the oxy- 

 hydrogen flame consists of Class I. and Class II. lines only. 

 There is no trace of Class III. lines in either the air-hydrogen 

 or oxy-hydrogen cones and mantles. The oxy-hydrogen spec- 

 trum, indeed, constitutes, as it were, a generally enhanced 

 type of the spectra given by the mantles of the air-coal gas 

 and oxy-coal gas flames, such as one would expect to obtain 

 by assuming temperature to be the governing factor in the 

 production of these radiations. That the temperature hypo- 

 thesis seems also to afford a plausible explanation for the 

 origin of the air-hydrogen spectrum, is supported by the 

 behaviour of the temperature lines W 3720, 3737, and 

 3746. These lines are apparently not affected by the 

 chemical actions in the air-coal gas cone and they appear 

 as feeble lines in the outer mantle of the same flame. In 

 the vicinity of the air-hydrogen cone they become much 

 brighter and in the oxy-hydrogen name, the hottest of these 

 three flames, they figure among the strongest lines of the 

 whole spectrum. These lines are evidently sensitive only to 



