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



the space below, forming bright and most sharply defined 

 spiral or other paths, such as might be expected to result 

 from the action of a magnetic field upon a stream of 

 luminous particles carrying electric charges. 



§ 6. Origin of the red fringe. 



It may be useful, at this stage, to briefly inquire into the 

 nature of the vehicles which convey the electric current in 

 the red fringe. It is well known from the work of many 

 physicists, in particular from Professor Richardson's extensive 

 researches, that at temperatures much below that at which 

 the red fringe is formed, electric currents are passing 

 through the ionized vapours or gases in the neighbourhood 

 of an electrically heated carbon rod or metal wire. It is 

 generally assumed that these currents are caused by the dis- 

 placement of ions under the influence of the acting electric 

 field, and Professor Richardson has therefore proposed to call 

 them thermionic currents. There is no doubt that the 

 electric currents, which I was able to register between two 

 exploring electrodes held in the luminous vapour beneath 

 the heated plate, at the lower temperatures (see § 4) were 

 of this nature. Now, these currents do not seem to have 

 any appreciable influence upon the character of the spectra 

 emitted by the vapours, which, as will be shown later, are 

 practically identical with those given by these same vapours 

 in the outer mantles of flames. But also in other respects 

 the thermionic currents differ greatly from the current 

 which causes the red fringe — namely in a transverse 

 magnetic field they are much less acted upon than the 

 latter. Whereas the red fringe is extremely sensitive to 

 the magnetic force and a field of a very few units suffices 

 to produce a distinct spiral or helical path, a field of at least 

 500 units is necessary to form an ill-defined and relatively 

 undeveloped curved path in the luminous vapour with ther- 

 mionic currents. It seems to me that this difference in 

 behaviour between the thermionic current and that causing 

 the red fringe might possibly be accounted for by assuming 

 that the particles which convey the electric current are of 

 different masses in the two cases. Thus, whereas the ther- 

 mionic current is probably due to the motion of relatively 

 heavy particles, in this case perhaps carbide molecules, the 

 current in the red fringe would arise from the displacement 

 of relatively light particles. These are perhaps constituted 

 of free radiating atom-ions formed by the electrons which 

 emerge in large quantities from the hot graphite plate, and 

 the paths of which are under the control of the magnetic 



