( 600 ) 



Zeeman^) have proved that in the iieip;hbourhc)od of the hands which 

 exhibit the ZKEMAN-phenomenon, (he rotation of the plane of polari- 

 sation on both sides of the band is positive, and in the inside of 

 the magnetic doublet negative. The experiments made with uniaxial 

 crj^stalsV with tlie axis placed parallel to the liiies of force and to 

 the beam of light either at the ordinai-y temperature, or at the tem- 

 perature of liquid air, have proved that the rej^ular change of the 

 magnetic rotatory power with the wavelength of the light is sub- 

 jected to a disturbance of the same kind on both sides of the band, 

 and to an opposite disturbance at the middle of the band. This 

 disturbance is positive outside the band for the bands belonging to 

 negative electrons, and negative for the bands of positive electrons. 



At the temperatures of liquid and solid hydrogen the same pheno- 

 mena are observed, at least when the asymmetry of the left- and 

 right-handed components is not too large. In the neighbourhood of 

 some bands whose components are very unequal, opposite disturbances 

 are observed on both sides of the band — as is easily explained 

 by means of the usual tigures of the anomalous dispersion. These 

 phenomena are clearly visible on the tigures. 4 PI. lil and 5 PI. IV. 



These figures have been obtained by a method which was already 

 used in former experiments '). Against the slit of the spectroscope a 

 Babinet compensator was fixed betweeji two crossed Nicols in such 

 a way that the fringes were perpendicular to the slit. Before the 

 compensator a plate of a quarter of a wa\'e-leng(li is placed in such a 

 way that the two opposite circularly polarized vibrations are changed 

 into two rays rectilinearly polarized ))arallel and normal to the 

 principal direction of the compensator. The deviations of the fringe in 

 the spectrum in the neighbourhood of the bands are proportional 

 to the difference of phase of the circularly polarized rays in the 

 crystal plate. 



In the tigures we tind for band 522.15 tig; 4 the symmetrical 

 case, tor band 523.7 tig. 4, and 642.3 tig. 5 the dissymmetrical 

 case with disturbance in the same direction, for band 537 tig. 4, 

 and 654.2 tig. 5 the opposite disturbance on both sides of the band. 



h. Compouml hands. The phenomena of absorption at lower tem- 

 peratures have shown that several bantls may be resolved into two 

 or more. These components behave ditïerently with respect to the 

 magnetic field, because some belong to positive, others to negative 



1) Arch Need. Vil p. 465. 1902. 



2) Jean Becquerei., Radium IV No. 2 p. 49. 19Ü7, V No. 1 p. 5. 19U8. 

 ■^) Jean Begquerel, G.R. May 21 1906. 



