( !^4 ) 



wliieli is entirely plano polarised, the plane of' polarization being' 

 perpendicular to the lines of force. 



Then, at the place in question, there will not be any luminous 

 motion produced by 3)?^, and, because the molecules are vibrating 

 independently of each other and hence lig-ht emitted by one can 

 never be totally destroyed by that orig-inating from another, ^s must 

 vanish in all molecules. Of course the same argument applies to ?0ï?/ ; 

 hence it follows, that no light can be observed from any point of 

 OX, that is to say in the direction of the lines of force. 



Becquerel and Desla.ndres have found ^) that one of the iron 

 lines, when viewed across the lines of force, becomes a triplet, the 

 central and side components of which, as compared with tliose of 

 the ordinary triplets, have interchanged their states of polarization ^). 

 The foregoing reasoning entitles us to predict, that only the middle 

 component of this triplet will be visible, when the phenomenon is 

 observed in the direction of the lines of force. 



§ 6. In the paper cited above, I have established the equations of 

 motion for infinitely small vibrations of a molecule, having n degrees 

 of freedom, and placed in a magnetic field. I called ^^i, p2j • • • P» 

 the general coordinates, chosen in such a manner, that they are 

 in the position of equilibrium, and that they are principal coor- 

 dinates as long as there is no external magnetic force. I obtained 

 for the equations of motion 



«IPJ +*^l?'l — (C1.2P3 + <^1.3/>3 + ••• +Cl.„p„) = 0, 

 «2 P2 + ^3F2 — (fa.! Pi -{- C2.3P3 + . . . + C2.nPn) = 0, 



• (1) 



etc. 



where a and b are constants, independent of the magnetic force. 

 The influence of the field is expressed by means of the terms con- 

 taining the quantities c, which are all proportional to the intensity 

 of the field. 



They further satisfy the relations 



(2) 



To determine the possible periods of vibration, we put, according 

 to a known method, in (1): 



') Coraptes rendus, -l avril 189S. 



'j The same plieiiomenon has been observed in the case of some iron-lines by 

 Ames, Karhaet and Reese, Johns Hopkins Univ. Circular. Vol. 17, No. 13.5. 



