Titanium , and Vanadium by Thermeleetronic Currents. 279 



with regard to class III. group 4957 of iron. The stronger 

 electric actions in Dr. Kin^s furnace have brought this 

 group out at already 1800° C, whereas in my furnace it 

 shows onty at over 2500° C. when the acting electric field 

 reaches about the same value as that prevailing in Dr. King's 

 furnace already at the lower temperature. Further, the 

 enhanced spectroscopic effect due to the stronger electric 

 actions in the alternating current furnace, is proved beyond 

 doubt by Dr. King's observation that in his furnace the 

 cyanogen bands are strong at 1850° C* Now, these bands, 

 which, as has been firmly established in the course of the 

 present research, are directly excited by the thermelectronic 

 current, are feeble in my furnace at about the same tempera- 

 ture, in fact only the head of the brighter band — namely 

 3883, has been detected at about 1900° C. 



It might be contended witli regard to the electric effect 

 of the alternating heating current, that the short duration of 

 the maximum value of the voltage reached twice during 

 each cycle may not suffice to appreciably affect the excitation 

 of spectrum radiations. Against this we have, however, the 

 very important experimental evidence by Dr. de Watteville 

 who, by a most ingenious method, has shown that the 

 spectrum emission follows very closely the periodic varia- 

 tions in an alternating current circuit f. But in this 

 connexion it is well to draw attention to the possibility of 

 the furnace temperature being likewise subject to periodic 

 fluctuations, owing to the rise and fall of the intensity of the 

 heating current. The temperature, as indicated by a pyro- 

 meter, would represent the average during a cycle ; but it is 

 just possible that the temperature, and therefore also the 

 degree of ionization, may momentarily reach a much higher 

 value than this, and this higher value would occur nearly 

 simultaneously with the maximum of the acting electric field. 

 Thus, in certain circumstances the running of an electric 

 furnace by means of alternating current may, also from this 

 point of view, affect the estimation of the true character of 

 the spectra emitted by the luminous vapours. It is probable, 

 however, that in a well protected furnace tube, temperature 

 variations of the kind here suggested will not be of great 

 amplitude; but, in the case of an unprotected tube, which 

 loses heat rapidly through radiation, such as is precisely the 

 cise in Dr. King's arrangement, the possible effects upon 

 temperature and ionization of the periodic variations in the 



* A. S. King-, Astroph. .Tourn. vol. xlix. p. 50 (1919). 

 t C. de Watteville. Comptes Rendu s de I' 'Academie des Sciences, seance 

 du 22 ievrier, 1904. 



