( 574 ) 



Has the middle line of " fri/dr/ the same vjavelength as die 

 unmodified line ? 



9. The change of wavelength here contemplated undoubtedly 

 must be extremely small, for no one of the physicists occupied with 

 the radiation phenomena in a magnetic field has, to my knowledge, 

 come across phenomena which decide the question put above tliis 

 paragraph . 



Some observations made with an echelon spectroscope have given 

 me evidence, that diiferent spectral lines and among these the mer- 

 cury lines undergo in very strong fields displacements of the order 

 of 6 or 10 thousandth parts of an Angstrom unit, in most cases 

 towards the violet. The matter seems of sufficient interest to be 

 treated in a separate paper, which I hope to give rather soon. 



Physics. — "Change of loavelemjth of die middle line of triplets." 

 (First Part). By Prof. P. Zeeman. 



1. In dealing with radiation in a magnetic field it has l)een 

 tacitly assumed by all experimentalists 1 know of, that the middle 

 line of triplets or of other symmetrical separation figures occupies 

 the same position in the S[)ectrum as the unmodified line. During 

 a rather detailed investigation of the asymmetrical separation shown 

 by some lines (see the paper immediately preceding) experiments on 

 the light emitted in the direction of the magnetic force showed that 

 symmetry was not always present where it was expected. 



The interest attaching to the encountered anomaly suggested the 

 question whether the original line is displaced during magnetisation. 

 The following paper gives sufficient evidence to assert that such is 

 the case. The asymmetrical position of the very weak line observed 

 between the components of the doublet of lijie 579J (see § 8 of the 

 paper immediately preceding) is not explained however by this dis- 

 placement. The contrary is the case. The theoretical interest of the 

 subject is probat)ly intimately connected with the existence of couplings 

 between vibrations parallel and perpen'^Hcular to the field ^). 



2. For the further discussion I will recapitulate here very briefly 

 the formulae -) giving for MiCHEiiSON's echelon grating the angular 



1) Cf. however Voigt. Annalen d. Phys Bd. 24, p. 195, 1907. 



2) MiGHELSON. Juuinal de Physique, (3), Vol. 8, p. 305, 1899. 



Fiirsl B. Galitzin. Zur Theorie des Stufenspectroscops. Bull, de I'Acad. Imp. des 

 Sciences St. Péteisbourg 1905 (5) T. 23. N^». 1 el 2. 



