Mr Waran, Ejfect of magnetic field on Intensity of spectrum lines 45 



The effect of a magnetic field on the Intensity of spectrum lines. 

 By H. P. Waran, M.A., Government Scholar of the University of 

 Madras. (Communicated by Professor Sir Ernest Rutherford.) 



[Read 8 March 1920.] 



[Plates I and II.] 



Since the discovery of the Zeeman effect the main attention 

 has been directed to the detailed study of the phenomenon of the 

 small change of wave length suffered by a monochromatic radiation 

 in a magnetic field. The question whether a magnetic field affects 

 the spectrum as a whole has not received much attention. 



While wiorking on the Zeeman effect with a mercury discharge 

 tube run by an induction coil as the source, a small portion of the 

 capillary tube being subjected to a magnetic field of about 5000 

 c.G.s. units as shown in Fig. 1, the light was observed to suffer a 

 change in intensity and also in colour opposite the pole pieces 

 when the field was thrown on. A spectroscopic examination revealed 

 the existence of some selective changes in the spectrum in addition 

 to the increased brilliancy of the general spectrum. It was also 

 noticed that the changes taking place varied considerably with 

 the pressure, at a low pressure the tube showing little change 

 visually but greater changes in the general spectrum. Attention 

 was concentrated on the latter. 



In the case of mercury which was the first spectrum investigated, 

 the tube, containing a trace of residual air at very low pressure, 

 gave the principal mercury lines, viz. : 



5790-66, 5769-6, 5460-7, 4916-0, 4358-34 

 and the principal hydrogen lines 



6563, 4861-5 and 4340-7. 



On applying the magnetic field, however, marked changes were 

 observed, including a new set of lines at 



5426, 5679, 5872 and 5889, 

 and a very strong red line at 6152, brought out prominently by 

 the field. Mercury lines have been recorded at these wave lengths 

 and these lines brought out are probably due to mercury. The 

 behaviour of the line 6152 was very remarkable. It was invisible 

 under ordinary conditions but showed up brilliantly in the magnetic 

 field, the effect being practically instantaneous. Exhausting the 

 tube still further and increasing the current through the tube to 

 about 5 m.a. Four faint lines appeared at wave lengths 

 6234, 6152, 6123 and 6072, 



