I'Kor.tGATIOS OF Ll.ix iiui i/.»/7;.V OITR THE li.tHTII 2n> 



of propa^^alion of the wa\c. This is, in fact, thv l)asis for the explana- 

 tion of the optic.il pro|H'rties of transparent and absorhinK media 

 and also of nu-di.i which show magnetic or other rotatory |M)wers. 

 Due to collisions aiul recomhinations, energy will pass continuously 

 from the electromagnetic held and increase the energy of agitation of 

 neutral molecules. Since this prcness is irreversible it accounts fyi 

 absorption of energy from the wave. 



Asiiume an electron or ion of charge e and mass m moving with 

 velcH-ity V and acted u|)on !)>■ an electric lield E and the earth's mag- 

 netic held H. The etpialion of motion of the free ion will be 



e c 



or av = E + vxh (1) 



in which h is written for — and a for w; e. (When we come to consider 

 c 



absorption it will be necess<irv to generalize </ into*/ (l — i — ) to in- 



dude a resisting force. n.\ proportional to the velocity.) 

 The total current is given by 



4irI = E+'^A7TXcv. (2) 



In these equations and the following we are using Gaussian units 

 .ind the summation refers to different kinds of ions. 



In order to avoid a complicated mathematical treatment, which, 

 however, is not difficult to carry through if necessary, it will be as- 

 sumed that the magnetic field H is along the axis of s. When more 

 general results are required, they will be stated. All time variables 



are assumed periodic with a frequencv - , so that =in. 



Solving equation (1) for the coniixuH-nts of v we find, for each 

 type of ion : 



inaX+hY 



