Physics. — -'The ionisatioii of argoii'. By G. Hoi^t and A. N. 

 KooPMANS. (Coininiinicated by Prof. H. Kamkrlingh Onnks). 



(Communicated in Die meeting of December 28, 1918). 



1. Franck and Hert//) have pointed out the fact that the con- 

 duction of electricity does not lake place in the same way in all 

 gases. They divide the gases into two groups: 1**' those, in which 

 an electron moving through the gas hardly loses any energy by a 

 non-ionising impact and 2"^^ gases, in which the energy of the 

 electron is lost for the greater part or totally by each impact. To 

 the first group especially the rare gases belong. Franck and Hertz 

 made themselves a series of measurements with these gases and 

 also gave a theory of the conduction of electricity by them. They 

 principally investigated heliimi. In the following we shall mention 

 the results of some measurements with argon. 



Untd now only determinations of Gu.L and Pidduck") existed on 

 this subject. A former investigation on the sjiark potential of argon 

 has taught us') however, that the results of these physicists are 

 not quite right, probably by a slight impurity of their argon. This 

 is probably the reason why the typical behaviour of the argon was 

 not pronounced in their measurements. 



2. We have again determined the connexion between current 

 and tension in argon. Our apparatus liad been constructed in the 

 same way as that of Gill and Pidduck (fig. 1). It consisted of a 

 coudensor, in which the variations in the plate-distance could be 

 measured. In the anode a series of holes had been bored through 

 which by means of a quartz lens ultraviolet light of a mercury 

 lamp could be concentrated upon the zinc cathode, in order to 

 liberate electrons from it foto-electrically. By means of a micrometer 

 screw the cathode could be moved up and down. The whole appa- 

 ratus had been fused into a glass tube with a quartz window to 

 let the ultraviolet light through. 



1) Verb. D. pbys. Ges. (15), 34, 929. 1913 en (16), 12, 1914. 



2) Pbil. Mag. (16), 280, 1908 en (23), 887, 1912. 

 ^) Versl. Kon. Ak. v. Wet. (26), 1027. 1917. 



