of Light Radiations emitted by Iron Vapour. 13 



gas flame, has an almost as far-reaching- effect on the atomic 

 systems concerned as the electric actions in the spark- 

 discharge. 



4. Classification on Lines based on their Relative 

 Behaviour in Flames. 



The results of all the measurements and observations were 

 tabulated so as to show at a glance the relative intensity 

 and character of each line in the various sources of light 

 examined. With the help o£ this table the lines were 

 classed according to their behaviour in the various flames, 

 and the following classification was provisionally adopted : — 



Class I. Lines which are emitted by the mantle of the 

 air-coal gas flame, and gain in intensity on 

 passing to the high-temperature flames. They 

 are specially sensitive to thermal actions, and 

 may be regarded as true temperature lines. 



Class II. Lines which are particularly sensitive to the 

 special chemical actions of which the explosion 

 region of the air-coal gas flame is the seat, 

 They are also, though feebly, emitted by the 

 outer mantle. In the flames of higher tern- 

 peratures their intensities increase, showing 

 that they likewise respond to thermal changes, 

 but to a lesser degree than Class I. lines. 



Class III This class contains the bulk of the cone lines 

 which form what M. de Watte ville and myself 

 had called the > supplementary spectrum. 



The following lists contain lines of Classes I. and II. only. 

 Those of Class III., for the same region of the spectrum, 

 can easily be obtained from de Wattevi lie's table by elimi- 

 nating the lines given here. The lines near the extremities 

 of the spectrum appear all relatively feeble. This is due to 

 the absorption of the glass in the ultra-violet, and to the low 

 sensitiveness of the photographic plates employed to the 

 green part of the spectrum. Wave-lengths are expressed in 

 international units. Lines to which an asterisk is affixed 

 are marked on Plate I. figs. 1, 2, & 3 to the nearest 

 unit. 



