140 THE ROYAL SOCIETY OF CANADA 



corresponding to a fall in potential of about 31 volts a bombarding 

 electron has sufficient energy to ionize the argon atom and to disturb 

 a second electron to a certain degree. As the voltage is further 

 increased the second electron is removed to a greater distance from 

 the nucleus, but it is difficult to say at what voltage the atom is 

 doubly ionized by the complete removal of two electrons. 



There is also the possibility of removing more than two electrons 

 from the atom and it w^as thought that a new type of spectrum might 

 be brought out by increasing the accelerating potential. A photo- 

 graph was taken with a grid voltage of 240 volts, but the results were 

 negative as no new lines were brought out. 



VI. Summary 



1. The radiation produced in argon by electron bombardment 

 with an accelerating potential of 10.1 volts has been detected photo- 

 graphically, and a table of wave-lengths is given. 



2. With accelerating fields varying from 16 to 30 volts the lines 

 in the arc spectrum were found to belong to the red argon spark 

 spectrum. 



3. As the grid potential was further increased to 31 volts the 

 blue or enhanced spectrum began to appear. At 54 volts apparently 

 all the lines in the enhanced spectrum were in evidence as predicted 

 by the Bohr theory. 



4. An attempt was made to bring on a third type of spectrum 

 by use of a grid potential of 240 volts. The results of this experiment 

 were negative as no new lines appeared. 



B. On the Ahsorptio7i Spectrum oj Argon 



I. Introduction 



In a recent paper on the ionized spectrum of potassium. Professor 

 McLennan^ has shown that a moderate electrodeless discharge in 

 potassium vapour produces a spectrum presumably due to the singly 

 ionized atoms, which exhibits a striking similarity to the arc or red 

 spectrum of argon. He has also show^n that when potassium vapour 

 is excited by a violent electrodeless discharge a new spectrum appears 

 which resembles to a marked degree the enhanced or blue spectrum 

 of argon. These experiments strongly support the theory suggested 

 by Sommerfeld,^ that the enhanced spectrum due to the singly ionized 



'McLennan, Proc. Roy. Soc. A, Vol. 100, p. 182, 1921. 

 *Sommerfeld, Atombau und Spektrallinien, p. 296. 



