266 Mr. G. A. Hemsalech : Excitation of Spectra of Carbon, 



facts. Thus we are led to conclude that a magnetic force 

 acting upwards, such as is provided by the magnetic field 

 due to the heating current, is responsible for the sharply 

 defined edge which characterizes the red fringe. 



§ 9. Displacements of red fringe emission by transverse 

 magnetic fields. 



In accordance with the assumption made in § 7 — namely, 

 that the red fringe emission is controlled by the therm- 

 electronic current, its characteristic spectrum lines and 

 bands should be observed to lengthen or shorten whenever 

 a magnetic field is brought to act upon the current in a 

 downward or upward sense. A large number of photo- 

 graphic records of the fringe spectrum in the presence 

 of a magnetic field have been secured and all, without ex- 

 ception, show up the intimate connexion between the fringe 

 emission and the thermelectronic current. A few selected 

 records are reproduced on Plates III. to V. Those on 

 Plate III. were obtained at a temperature of about 2700° C. 

 a shows the normal development of the spectrum in the 

 violet and ultra-violet regions without the action of a 

 magnetic field, other than that due to the heating current. 

 As already mentioned in § 5, the red fringe is not visible 

 under these conditions, since the red bands come out only at 

 the higher plate temperatures. But the carbon bands at 

 3883 and 4216, as also numerous titanium lines, are quite 

 conspicuous, although they pass down only a relatively short 

 distance as compared with a on Plate II., which was obtained at 

 a temperature of 3000° C. The sharply bordered continuous 

 emission extending downwards from the graphite plates on 

 a and c is due to the bluish vapour described in § 4, which 

 in these two cases was particularly intense near the lower 

 edge, b shows the effect of a magnetic field of 175 C.G.s. 

 units acting downwards, i. e. in opposition to that set up by 

 the heating current. All the bands and lines of the fringe 

 spectrum now reach much farther down from the plate and 

 pass into regions where the temperature must be considerably 

 lower. A word of explanation is due here with regard to 

 the strong continuous spectrum and the marked lengthening 

 of the lines emitted by the luminous vapour. These are 

 caused, as will be shown in the next communication, by the 

 spiral paths along which the luminous particles move under 

 the combined influence of the electric and magnetic fields. 

 c was obtained under similar temperature conditions as b and 

 with a magnetic field of the same strength, but with the latter 

 acting upwards, i. e. in the same sense as the magnetic field 



