for Production of Luminosity in Atmospheric Neon. 931 



20'0 volts and 22'8 volts, and the excitation of the lines of 

 the principal and subordinate series respectively, many series 

 of observations of the currents between the different electrodes 

 were made at the same time as observations of the spectrum 

 of the glow w T hen the electron velocity was varied. Examples 

 of some of the curves obtained, with the points at which 

 representatives of the two groups of lines first appeared, are 

 given in figs. 3 and 4. 



The series of observations represented in fig. 3 was taken 

 with the grid and anode connected together and to one 

 terminal of* the galvanometer, the other galvanometer terminal 

 being connected through the battery to the negative end of 



Fig-. 3. 



15 IS 20 £Z 



Electron velocity, voJfs 



the filament. Thus the electrons, after being accelerated up 

 to the grid by the applied potential difference, passed into a 

 field-free space and, when the ionization velocity was reached, 

 were able to produce ionization over a considerable distance. 

 Hence, with this arrangement, the luminosity when it first 

 appeared extended over a much bigger length of the distance 

 between the grid and anode than was the case when the 

 electrons were retarded between these electrodes. The 

 current measured by the galvanometer is, with this arrange- 

 ment, the total current passing between the filament and the 

 other two electrodes. The curve of fig. 3 shows three bends : 



