THE 



LONDON AND EDINBURGH 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



b 



[THIRD SERIES.] 



MAY 1839. 



L. Researches in the Vndulatory Theory of Light, continued; 

 on the Elliptical Polarization produced hy Quartz. Part II. 

 By J. TovEY, Esq. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 

 TN the former part of this investigation (present volume, 

 •■- p. 172) the terms involving A3, A'g, were supposed to be 

 insensible; but the comparison of the results of the calcula- 

 tion with the observed phasnomena, by which every supposi- 

 tion ought to be verified, affords no proof of this; for if we 

 restore tlie neglected terms, by adding respectively, to the 



expressions (21.), - A3 -^^) -A'3-^, and (26.) 



half the same values divided by A;*, the expression (27.) vvill 

 still result by neglecting merely the difference of those terms. 



We must also observe that there is nothing to determine 

 whether the equations (19.), (20.), give p^ = — 1, po = I, or 

 p = 1, p^^ = — 1. But, sinjce Bj P is incomparably the 

 largest term in 0-', the sign of this quantity must depend on 

 tliat of B^; therefore, since the signs of p^, pg, depend, by 

 (20. j, on that of a', it follows that they also depend on that of 

 B2 . This circumstance shows that a change in the sign of 

 B2 does not affisct the signs of the last terms either in (18.), 

 or in (21.), and (26.), derived from (I^.). But, since a change 

 in the signs of p^ , p^ , causes a change in those of ^ and tan 

 a, by (22.) and (23.), it follows that, although a change in 

 the sign of B., does not affect the velocities v^ , Vj , it causes 

 a change in the direction of the angle a, through which the 



J'hi'l. Mfif;. S. 3. Vol. 14.. No. 90. May 1839. Y 



