138 THE ROYAL SOCIETY OF CANADA 



IV. Results 



Photographs were taken with the following accelerating poten- 

 tials: 10.1, 16, 19, 30, 31, 37, 40, 45, 55, 90, 105 and 240 volts. At 

 10.1 volts, which was the minimum voltage for radiation, the following 

 lines belonging to the argon red spectrum appeared: 



Intensity 





 

 1 

 2 

 2 

 1 



A reproduction of the photograph taken is shown in Plate 1(a). 

 The faint lines are the ones whose wave-lengths have been given 

 while the bands occurring at the wave-lengths 3806.4, 3562.0 and 

 3347.9 A.U., which are plainly seen in the photograph, are probably 

 due to traces of gas impurities from the wax used with the quartz 

 window. These bands did not appear in the other photographs 

 taken with higher accelerating potentials, which was doubtless due 

 to the much greater relative intensity of the argon arc. The fact 

 that this radiation appeared with an accelerating potential of 10.1 

 volts, whereas the resonance potential has been found to be 11.5 

 volts,^ is due to the initial energy of the electrons as they came out 

 from the heated filament, for which no correction was made. 



Plate \{b) shows a reproduction of the spectrum obtained with 

 a grid voltage of 16 volts, which is approximately the ionization 

 potential of argon. At this voltage a large number of lines, all 

 belonging to the red argon spectrum appeared, the intensities of 

 the various lines, of course, being somewhat different from the red 

 spectrum produced by passing an induction coil discharge through 

 an argon discharge tube, a reproduction of which is shown in Plate 

 1(c). This agrees with the results of Déjardin and indicates that the 

 red argon spectrum is due to the return of a single electron which has 

 been removed by the bombarding electron moving with a speed corre- 

 sponding to a fall in potential of 16 volts, or in other words, the red 

 argon spectrum is produced by a recombination of a singly ionized 

 argon atom with an electron. The photograph in Plate l{d) shows 

 the mercury arc spectrum for wave-length comparison. 



^Horton and Davies, loc. cit. 



