38 L. B. Tuckerman 



By substituting- in (64) there results after a slight reduction 

 2e o X.g2-rrA T A- sin 27rA ? ] sin 2 \j/ — 2sin 2 7rA^ tg2irJVsm 2 2%[> 



1 — e- o 1 — 2sin* J 7ry\j — sin 271-7^ tg 27rA r sin2 \p 



As before, if *p =ip for <f =o: 



^ o = — ^2 sin 2 7r A r , ( sin 2 \p- — sin 2 ^ ) ( 1 — ^ 2 ) 



1 — tg^A 7 , tg27rA T ( sin 2^ -{-sin 21/^) 



(67) 



(68) 



1 — 2 sin a 7rA^ — sin 2 7r A r j tg2 7r A r sin 2 \p 



or, introducing approximations for c o and sin 2^: 



e== — tg7rA r 1 (sin2i/' — sin2«//J ( i-ftg'-VA"— sin 2 7rA 7 1 cos 2 2i/' — . . .) 



to quantities of the second order in N and A\. The correction 

 factor may be neglected, provided tg 2 v JV-j- sin 2 7r N y is negligible in 

 comparison with 1. Then 



e o = — tg7rA r 1 (sin2</' — sin2i/> o ) (69) 



In case large cllipticitics are to be measured, the determination 

 of the azimuth of the major axis of the ellipse becomes of impor- 

 tance, and the difficulty of determining it with the preceding ar- 

 rangement renders the method valueless. For measuring large 

 ellipticities, Mr. A. Q. Tool has devised an arrangement involv- 

 ing the measurement of the double rotation of compensator and 

 analyzer, which is analogous to Stokes's method, and in fact may 

 be considered as an application of the halfshade principle to 

 Stokes's analyzer. 



The analyzing nicol is replaced by a halfshade system of the 

 Lippich type (split nicol, Lippich, or. for greater sensibility, a 

 Brace sensitive strip), which will be designated simply as the 

 "Lippich.'' The elliptic halfshade (which will be designated as 

 before, simply "the halfshade"), instead of being fixed relative 

 to the incident light, is fastened to the Lippich and rotates with 

 it, i. e. in the previous notation, 2^(2,3) is constant. The divid- 



194 



