Spectrum produced by External Magnetic Forces. 59 



interpretation that the dark space is of the nature of an ab- 

 sorption-band. Indeed, one should expect to see also reversal 

 if looking across the lines of force. However, in this direction 

 no trace of an ordinary absorption-line was visible with the same 

 magnetic intensity. Hence we must conclude, I think, that 

 I have really observed the doublet indicated by Lorentz's 

 theory. 



10. Looking across the lines of force I succeeded in observing 

 the phenomenon indicated as triplet a (§ 6, diagram). If no 

 nicol was used only a broadened line was visible. A nicol 

 oriented so as to get rid of light whose plane of polarization is 

 vertical makes a dark well-defined line appear in the midst of 

 the broadened line. Turning the nicol over 90° this dark line 



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disappears, the lateral wings now being quenched, because 

 these are polarized in a horizontal plane. All this is to be 

 expected according to § 6. The analysers in § § 9 and 10 

 were inserted according to Lodge's * advice before the light 



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reaches the grating. 



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Till now I have not had the opportunity of measuring the 

 intensity of the field used in §§9 and 10. I took care, 

 however, to make them nearly equal in the two cases. 



11. Finally it may be mentioned that 1 observed also 

 traces of the phenomena described in §§9 and 10 with 

 sodium. As the D-lines reverse so very easily by non- 

 magnetic agency and as they show sometimes complicated 

 phenomena (Lockyer aud Ciamioianf), it seems difficult to see 

 the phenomena pure and simple with sodium. It is true that 

 it is not difficult to avoid perturbations caused by the motion 

 of the piece of asbestos, as mentioned by Egoroff and 

 Georgiewsky % in their interesting note. To avoid disturb- 

 ances of this kind I simply moistened tlie mouth-piece of the 

 burner with a very concentrated solution of JSaOl or NaBr. 

 Small disturbances nevertheless easily make their appearance. 



12. Although my inquiry is not yet closed, I think, how- 

 ever, that we can say that it seems to give new evidence in 

 favour of the interpretation of the magnetization of the spectral 

 lines given by Lorentz's theory. When I have determined 

 the intensity of my field, we can decide the question whether 

 we can hope to obtain a pure triplet by augmentation of the 

 magnetic force or by using narrower spectral lines, though, 

 of course, it may yet turn out that the phenomena prove to 

 be less simple. For a future paper also must be reserved the 

 accurate measurement of the amount of the magnetic change 



* ' The Electrician ' of 26 February, 1897. 

 f ef. Kayser, Spectralanalyst ', p. 305. 

 X C. It. t. cxxiv. p. 949. 



