314 Mr. Gr. A. Hemsalech on the Luminous Vapours 



3. In the absence of sufficient quantities of ionized 

 vapours, strong magnetic fields of from 1500 to 2000 c.G.s. 

 units must be applied in order to appreciably displace the 

 red fringe emission. Consequently, the conclusion arrived 

 at in § 8 of my preceding paper — namely, that the sharp 

 outline presented by the red fringe and its spectrum emission 

 are caused by the magnetic field due to the heating current — 

 becomes untenable. Although no satisfactory alternative 

 explanation of this peculiarity of the fringe is offered, it is 

 pointed out that most luminous phenomena which owe their 

 origin to the flow of an electric current at atmospheric 

 pressure present a sharp outline. § 2. 



4. It is shown that the vapours which fill the protected 

 space are in great part derived from substances placed upon 

 the plate. The formation of striae at the boundary surface 

 of the protected space is interpreted as indicating that the 

 vapours pass round the plate in a helical path. It is further 

 suggested that such a path might be caused by the combined 

 actions of the electric and magnetic fields set up respectively 

 along and around the plate by the heating current. § 3. 



5. A short discussion concerning the probable cause of 

 the downward drift of the luminous vapour in the protected 

 space has led to the suggestion that it might be due either to 

 gravity or radiation pressure, or possibly even to the com- 

 bined action of both. § 4. 



6. A convenient method has been developed of readily 

 ascertaining the relative sensitiveness of a spectrum line to 

 thermo-chemical and thermo-electrical excitation. Accord- 

 ing to this method the character of a line is revealed by its 

 relative intensity in fringe and luminous vapour. For the 

 purpose of facilitating the grouping of lines having similar 

 character three distinct types, based on their shape and 

 appearance, have been adapted as standards — namely, long 

 lines, tadpole lines, and short lines. The experimental 

 arrangement underlying this method may be appropriately 

 called a single plate resistance-furnace. § 5. 



7. An investigation of the spectrum lines emitted by the 

 vapours of magnesium, copper, and manganese has brought 

 out the fact that the line emissions due to thermo-electrical 

 and to chemical excitation are both of the same type — 

 namely, the lines most strongly affected by the therm- 

 electronic current in the fringe are precisely those which 

 are characteristic of the explosion region of the air-coal gas 

 flame. Their sensitiveness to electrical stimulation is further 

 illustrated by the fact that their emission is appreciably 

 enhanced in a capacity spark. §§6, 7, and 8. 



8. The characteristic flame lines of magnesium, copper, and 



