218 JONES-STRONG— THE ABSORPTION SPECTRA [April 24. 



nection with the atom. Most of the neutraHzing electrons will 

 probably lie far within the atom. For instance, we would expect 

 that in the uranium atom the charged helium atoms are neutralized 

 by negative electrons. 



Our theory is that the finer absorption bands of such salts as 

 neodymium, erbium and uranium are due to vibrations of these 

 neutralizing electrons, and that the forces acting upon these are 

 considerably different from those acting on the ring electrons, 

 which, in many cases, give a normal Zeeman effect. It is probable 

 that these neutralizing electrons play the greatest role in the optical 

 properties of bodies, such as the properties determining the index 

 of refraction, the extinction coefificient, etc. 



Usually the equation of motion of such an electron is given by 

 an equation like the following when a light wave of an electric 

 field E cos pt is passing by it: 



/f ^jQ (ioc 



m -^^^ -\- k -z- -\- n^x = E cos //. 

 at at 



where m is the total mass (electromagnetic and material) of the 

 electron, k • dx/dt is the damping or frictional term and vrx is the 

 quasielastic force. It is an experimental fact as shown by the 

 above work and the work of other investigators, that k and n- are 

 not only functions of the electron and the atom, but that they are 

 also functions of the physical and chemical conditions existing in 

 the neighborhood of the atom. 



On the other hand, the effect on k and n- for a ring electron, 

 when external physical and chemical conditions are changed, is 

 very small. It is for this reason, and the probable fact that there 

 are relatively few neutralizing electrons, that we believe that much 

 greater progress can be made in determining some of the properties 

 and constitution of various interatomic systems of atoms and 

 molecules by the study of the absorption spectra of uranium and 

 neodymium than by a study of the arc or spark spectra of the same. 



The method of attacking the above problem will be to study the 

 effect on the spectra of a body produced by changing the physical 

 and chemical conditions about the light absorbers or emitters within 

 as wide ranges as possible. Some of the possible changes that 



