834 Mr. Gr. A. Hemsalech and the Gomte de Gramont on 



It will hardly be necessary to remark that, along this line 

 of argument, when the frequency of the incident wave is 

 very near to that of proper oscillation of the electrons in 

 atoms, there takes place a resonance phenomenon, and as the 

 result of this there may be expecfed to occur such pheno- 

 mena as ionization and resonance radiation of the gas, and 

 the incident energy thus being consumed by a considerable 

 amount, the spectrum line corresponding to this frequency 

 will be missing, which is called an absorption line in the 

 ordinary spectroscopy. 



Physical Institute, College of Science, 



Imperial University of Tokyo, 



Sept. 20, 1921. 



XCIV. Observations and Experiments on the Occurrence of 

 Spark Lines (Enhanced Lines) in the Arc. — Part II. 

 Magnesium, Zinc, and Cadmium. By Gr. A. Hemsalech 

 and A. be Gramont *. 



[Plates XVII.-XXL] 



Contents. 

 § 1. Introduction. 

 § 2. Influence of the nature of the liquid film upon the emission 



of various types of lines in the arc. 

 § 3. Effect of high voltage currents. 

 § 4. Thickness of liquid film at moment of rupture and relative 



durations of first and second phases. 

 § 5. Effects of gaseous media. 

 § 6. Arc in liquid air. 

 § 7. Cause of broadening of the hydrogen lines during the first 



phase. Stark effect. 

 § 8. Detailed results of observations on the arc spectra of 



magnesium, zinc, and cadmium. 

 §9. Explanation of Plates. 

 § 10. Discussion of results. 

 §11. Summary. 

 § 12. Concluding remarks. 



§ 1. Introduction, 



A S a result of an experimental investigation of the 

 jljL arc spectra of lead and tin described in an earlier 

 communication f we arrived at the conclusion that the 

 emission of spark lines (enhanced lines of the fourth type 

 of Hemsalech's classification) by the arc is connected with 

 the presence of strong electric fields. Further, we showed 

 that when the temperature of the medium is raised, by 



* Communicated by the Authors. 



f G. A. Hemsalech and A. de Gramont, Phil. Mag. ser. 6, vol.xliii. 

 p. 287 (1922). 



