THEORY OF THE DISPERSION OF LIGHT. 
159 
Hence, following the same investigation as in my former paper*, we arrive at for- 
mulae corresponding to (25.) (26.) (2/.) (28.), whence there results, 
0 = — 2 {a p sin 2 6} 
0 = 2 {p' sin 2 0} (8.) 
— n 2 = 2 {p' 2 sin 2 0} J 
and the formula corresponding to (41.) gives 
sin b = — 
(9.) 
Hence, it follows that in the case where the ray coincides with an axis of elasticity, 
the criterion of elliptic polarization ceases to be applicable. 
* In the formula (17.) of my former paper, an oversight was discovered, too late to be corrected, in the siyn 
of the last term, which should be + instead of — . This error runs through all the succeeding forms, and 
causes the introduction of the factor (cos 2 b) in (29.) (30.) and (31.) j this factor should be unity. This 
error, however, does not in the least affect the ulterior results. 
Also in p. 255, line 7 from bottom, for /3 = 0, read b — 0. 
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