932 Prof. Horton and Miss Davies on Electron Velocities 



the first at about 17 volts indicating the beginning of 

 ionization, the second at 20*5 volts indicating an increased 

 production of ionization, and the third and most marked 

 bend at 23'0 volts denoting a still further increased pro- 

 duction of ionization. The first appearance of luminosity 

 occurred between 21'2 volts and 2T4 volts, the yellow line 

 X 5852 being then visible in the spectroscope. At 21*65 volts, 

 X 5401 and the other lines of Table II. were discernible. 

 At an electron velocity of 23*1 volts the lines X 5341, X 5331, 

 and X 5031 could be seen faintly ; and at an electron velocity 



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1etc. 



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A 5 



HZ 



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11 



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Elechron velocity, volfS. 



of 23'5 volts all the lines of Table III. could be seen, and the 

 whole spectrum was much brighter. For this series of obser- 

 vations a fairly strong magnetic field was used for the 

 concentration of the luminosity. 



In fig. 4 a series of observations of the ionization current 

 and spectrum variations with alteration of the electron 

 velocity, in the absence of a magnetic field, is represented. 

 The arrangement of electric fields was very similar to that 

 used in obtaining the curve of fig. 3. As was to be expected, 



