Interferometer Study of Radiations. 43 



II. (1) The interferometer is capable of showing the mag- 



netic effect for field strengths below 1,000 C.G.S. 

 units. 



(2) The visibility curves,^ even under unfavorable cir- 

 cumstances, show clearly the general character of 

 the magnetic action, and when checked through a 

 long series by means of an harmonic analyzer- fur- 

 nish an incomparable method of analysis. 



(3) When unaccompanied by such a check, and for 

 quantitative measurements of change of wave-length 

 another use of the interferometer furnishes a better 

 method. 



III. (1) At the temperature of the Bunsen flame there is 



a distinct ionic "lag" or constraint Avhich is sud- 

 denly overcome, at a field strength of 9,500 C.G.S. 

 units. 



(2) This ionic lag becomes less as the temperature 

 rises and is practically absent at the hottest tem- 

 perature of the oxj'-hydrogen flamo, or of the 

 vacuum tube. 



(3) The change in wave-length reaches a maximum 

 value, depending upon the temperature, at about 



11,000 C.G.S. units. For values of magnetic field 



above this the effect is to broaden the component 



lines and not to further separate them. 



This latter point may be peculiar to sodium and due to the 



simultaneous presence of the lines D^D^. No observations 



have yet been made upon these lines separately, the dispersion 



necessary to isolate them being too great. 



Measurements of Magnetic Shift. 



The equation expressing the relation of the change of 

 wave-length (/- — ''•') to the strength of the magnetic field 

 (H) producing it is 



-,.'={e;,.;L^H, 



>Phil. Mag. (5), 44, pp. 100-115, 1897; (5), 45, pp. 348-356, 1898. 

 'Phil. Mag. (5), 45, p. 85, 1898. 



