Section III, 1922 



[151] 



Trans. R.S.C. 



The Electrodeless Discharge in Iodine and in Hydrogen 

 By John K. Robertson 



In a paper now in the press/ the writer has given results of a 

 spectroscopic study of the discharge excited in certain vapours by 

 electromagnetic induction. In the case of iodine, the only diatomic 

 vapour studied, it v/as found that, as the electrical excitation was 

 gradually increased, a stage was reached at which a sudden and 

 marked change in the character of the discharge took place. It 

 seemed desirable, therefore, to extend the investigation to other 

 diatomic vapours and gases, and especially to hydrogen, whose com- 

 plex secondary spectrum still awaits a satisfactory interpretation. 



The experimental arrangement differed little from that first used 

 by Sir J.J. Thomson. A bulb of capacity about 1 litre was suspended 

 inside a coil of six co-planar turns of s,t0ut copper wire through which 

 passed the high-frequency discharge of two "half-gallon" Leyden jars 

 connected as shown in the diagram. The jars were charged by means 

 of a small interrupterless X-ray transformer T, while the spark gap S 

 enabled one to vary the intensity of the eoccitation. It is important 

 to note that at any point within the ring the mean electrical intensity 

 is directly proportional to the potential at the spark gap and inde- 

 pendent of the capacity.^ It is possible, therefore, by gradually 

 lengthening the spark gap, to subject the gas or vapour to a steadily 

 increasing electrical intensity and in this way study the change in the 

 appearance of the discharge resulting from changing excitation. 



ij. K. Robertson, Phys. Rev. XIX 5 p. 470 May 1922. 

 «Bergen Davis, Phys. Rev. Vol. XX, p. 129, 1905. 



