296 Origin of Line Spectrum emitted by Iron Vapour. 



to excite characteristic line radiations. It would therefore 

 appear premature to establish a temperature classification of 

 the spectrum lines of iron which would embrace the lines 

 observed in such sources as the high-temperature furnace 

 and the arc, in both of which the prevalence of electric 

 actions is so manifest. We know practically nothing about 

 the state of temperature of the radiating atoms in these 

 sources because all the measurements that have been made 

 refer to the inner wall of the furnace or, as in the case of the 

 arc, to the surface of the electrodes only. Further, all the 

 experimental evidence seems to point against the view that 

 the line emission in these sources is caused by direct thermal 

 actions. As my experiments show, iron vapour may indeed 

 be in a state of high temperature without emitting a line 

 spectrum. Both the high degree of temperature in the 

 vapour and the luminous vibrations of its atoms may, in the 

 arc and furnace, represent concurrent manifestations of 

 electric actions. On the other hand the results obtained 

 with thermo-chemical excitation, both in flames and furnace, 

 have revealed a gradual progression in the development of 

 the iron spectrum as the temperature rises and, between the 

 limits of 1500° and 2700° C, it should be possible, wherever 

 this mode of excitation exists, to determine the state of 

 temperature in the source from the degree of development 

 of its spectrum. But whether we should be justified in 

 deriving the state of temperature in an electrical source 

 by extrapolating the values found for flames, is not at all 

 certain. But supposing we did so, this would give us 

 roughly for the high-temperature furnace spectrum of iron 

 values of the order of at least 3000° if we judge by the 

 development of class III. lines. This figure represents no 

 doubt a possible result and, if such temperature determi- 

 nations could be confirmed by more direct methods, it might 

 perhaps lead to a closer coordination on the basis of equi- 

 valent temperature conditions, of the various modes of 

 excitation discussed here. 



Before concluding I desire to express my heartiest thanks 

 to Sir Ernest Rutherford for the many acts of kindness with 

 which he has favoured me and for the encouraging interest 

 he has taken in the work. 



My thanks are likewise due to Dr. Newbery for the 

 cordial welcome extended to me in the electro-chemical 

 laboratory. 



Manchester, May 20th, 1918. 



