( ^^"l ) 



q'l cos [ («3 -|~ "'2) ' 4" ^"'J 



anti 



g\ cos [ («3 + w'2) « + c' + I 7i]. 



On the other hand, there are at the same time a l>vibratiün 

 (/, cos [(?ii + ?i/) <+(■], 

 and a ]',-vibration 



1-i cos [(wj + «i')< + <■ + i ?i] . 

 ConsuUing the small table of the last Art., I find a vibration 

 3/4 y- qi q\ cos [ (;;3 — n^ + «3' — "1') < + <;' — c— ^/r] — 



— ^/i y- q\ q\ cos [ («2 — «1 + ^i' — «1') < + c' — c + i?i] = 



= ^/2 ^ 91 ïl' cos [ (??3 — «1 + ??3' — 7ii') i + c' — C — ^7l] 



parallel to OX, and a vibration 



^/4 y- qi ii' cos [(?i3 — 111 + «2' — «1') * + c' — c] + 



+ *^/4 >f qi q\ cos [ (»2 — ni -\- n^' — «i') t -\- c' — c] = 



=; % /< "71 9l' fOS [()'o — Hi + «2' — "1') t -\- c' — c) 



in the direction of OY. Hence, across the lines of force we shall 

 see light whose vibrations are perpendicular to the lines of force and 



9 



whose intensity may be put proportional to — ;<^ ^i^5'i'~. Since there 



4 



is a difference of phase of V4 period between the two secondary 

 vibrations, both together will produce circularly polarized light along 

 the lines of force. 



By similar reasoning it is found that the second of (17) and 

 the second of (18) do not produce any secondary vibrations. 



Examining all the 15 combinations, I find the following results, 

 as regards the radiation across the lines of force. 



A. There will be seen in the spectrum the following lines, whose 

 vibrations are parallel to the lines of force. 

 1. A. central line whose frequency is n^ — nj , and whose in- 

 tensity is proportional to 



q,' q'-o' [12] . 



