Titanium, and Vanadium by Thermelectronic Currents. 243 



heat only on the top surface, we should be enabled to 

 examine in a convenient manner the luminous effects pro- 

 duced by the ionization currents which always circulate in 

 the immediate vicinity of an electrically heated carbon con- 

 ductor — in this particular case, along the undersurface of 

 the plate. Experiments carried out in this way have com- 

 pletely confirmed the results of my previous investigation 

 with reference to the existence of the two emissions, and the 

 unquestionably electrical origin of one of them, to which is 

 due the spectrum of carbon, has been demonstrated beyond 

 doubt by the action upon it of a transverse magnetic field. 

 The evidence derived from these experiments indicates further 

 that the particular ionization current, which produces the 

 effect in question, is distinct from Professor Richardson's 

 thermionic current and is most probably constituted of a 

 stream of electrified particles of very small mass. I propose 

 to call this current the thermelectronic current in order to 

 mark its distinguishing character from the former. This dis- 

 tinction appears to me justified, not only by reason of the very 

 remarkable and definite spectroscopic effects produced, but 

 also on account of the most significant influence which feeble 

 magnetic fields exert upon the path of the thermelectronic 

 current. As will be shown in a subsequent communication, 

 the passage of thermelectronic currents through ionized 

 vapours in a direction at right angles to the lines of force 

 of a uniform magnetic field is accompanied b}^ the forma- 

 tion of most beautifully defined luminous path figures of 

 spiral and helical shapes. Furthermore, the cycloidal and 

 trochoidal forms of projection of these paths upon a plane 

 normal to the magnetic force, as foreseen by the electron 

 theory, are clearly brought out. 



As I have suggested in a preceding paper *, the high 

 temperature furnace spectrum of iron may be regarded as a 

 low tension arc spectrum, and it seems to me probable that 

 the value of the electric field provided by a tube-furnace is 

 about the minimum at which the atomic vibrations will be 

 excited by electric action, at these high temperatures. In 

 order to investigate the effects of stronger electric fields on 

 the spectrum emission of luminous vapours several types of 

 plate-furnaces have been evolved, which bridge the long gap 

 between the tube-furnace conditions and those prevailing in 

 the ordinary electric arc. Besides yielding most important 

 results with regard to the relative sensitiveness of spectrum 

 lines to thermo-electrical excitation, these plate-furnaces 



* Hemsalech, loc. tit. p. 211. 



R2 



