of the Flame and Furnace Spectra of Iron. 211 



could be so much higher than that of the mantle; for if it 

 were so, the temperature in the zone of the mantle in im- 

 mediate contact with the cone would naturally, by reason of 

 convection, be at least of the same order of magnitude as 

 that prevailing in the cone, and the luminous vibrations, if 

 really they were controlled by temperature, would be ob- 

 served to die out only gradually as the radiating centres 

 passed from the cone into the surrounding mantle. But, as I 

 have shown, this is not the case; for the characteristic cone 

 emission stops abruptly at the boundary surface of the 

 cone. 



With regard to the mantle of the air-coal gas flame and 

 those of the high-temperature flames, it is not possible to 

 reconcile the figures given by Drs. King and Bauer on the 

 basis of the experimental data so far available. It seemed to 

 me that the only way in which the question could be settled 

 was by a direct comparison between flame and furnace 

 •spectra made by the same experimenter. An opportunity 

 for carrying out this test presented itself last autumn at the 

 electro-chemical laboratory of this university, and with the 

 kind permission of Sir Ernest Rutherford I was enabled to 

 avail myself of the heavy current plant laid down specially 

 for furnace work. I may say from the outset that the results 

 of my investigation have established the existence of complete 

 •analogy between the characters of the flame and the corre- 

 sponding furnace spectra of iron up to a temperature of 

 about 2100° C; and, further, they have shown that 

 Dr. Bauer's results are in entire harmony with my own 

 observations. Above the boiling-point of iron, namely at tem- 

 peratures of over 2500° C, the furnace spectrum undergoes 

 a very radical change. I had always suspected that when 

 the furnace-tube is completely filled with metal vapour, the 

 latter, if of adequate conductivity, would of necessity, in 

 accordance with the fundamental electrical laws, carry part 

 of the electric current which is supplied to the furnace. My 

 experiments have brought most forcible evidence in favour 

 of this view, and I have now no hesitation in ascribing the 

 cause of the so-called high-temperature furnace emission of 

 iron vapour to electric actions ; it should indeed be classed 

 as a low-tension arc spectrum. 



The present and also the subsequent communication will 

 contain an account of my own observations and experiments 

 on the electric-tube resistance furnace. My observations, as 

 will be noted, go to corroborate in many respects those made 

 by Dr. King; but as a result of supplementary experiments 

 and thanks to the experience gained in connexion with 



P2 



