Spectra and Planclcs Law. 445 



the solution of these equations when f, 77, f vary as e pf is 



Ee cos pt , , a2 . a ., 



7?= ~"A^ —abe"p' — icp{iL — mp-)}, 



v E<?cosjd£ , 9 



£ = -r { — ac «y + i&p (yu, — m/? J ) j , 



where A = (jjl — mp 2 f + (fi— mp 2 ) e 2 (a 2 + b 2 + o 2 ) . 



We see from this that the displacements of the electron 

 are not wholly in the direction of the electric force ; but 

 from the form of the equations we see that if mp 2 is either 

 very small or very large compared with /*, the displacement 

 across the direction of the force is infinitesimal in comparison 

 with that along it. In the theory of scattering of visible 

 light mp 2 is assumed to be small compared with //,, while for 

 Rontgen rays it is assumed to be large, so that the magnetic 

 forces would not appreciably affect these types of radiation. 



If there are several electrons with their centre of figure at 

 the centre of the atoms, and if the axis of x is a principal axis, 

 then %ab, %ac, %c, and Xb vanish, and the scattered radiation 

 will be in the same direction as that given by the ordinary 

 theory for the non-magnetic atom. The effect of the trans- 

 verse displacements, if the electrons in one atom were 

 arranged unsymmetrically, so thatSafr, etc. did not all vanish, 

 would, if all the different atoms were orientated in exactly the 

 same way, produce a rotation of the plane of polarization 

 when plane polarized light passed through the collection of 

 atoms. This effect would, however, disappear if the atoms 

 were orientated at random. 



There does not, therefore, appear to be anything in the 

 scattering of light by the atoms of a gas or in the rotation 

 of the plane of polarization of light inconsistent with the 

 existence of a strong magnetic field inside the atom. 



Scattering of Cathode particles by the Atom, 



If the dominant forces inside the atom were magnetic, a 

 charged particle moving through the atom would be deflected, 

 but inasmuch as the force on a moving particle due to its 

 magnetic field is always at right angles to the direction of 

 motion of the particle, the particle would neither lose nor 

 gain energy. The collisions would be what are often called 

 elastic to distinguish them from those in which there is a loss 

 of energy, which are called inelastic. 



