How may the constants a, b, c corresponding to the axes of elasticity
be obtained experimentally?

If the two faces of a prism, formed of a biaxal crystal, be perpendicular
to each other, and one contain the two axes of elasticity a, 0, and the
other by c; and if fi a , ii h be two refractive indices for the ordinary ray
when the planes of refraction are perpendicular to the axes a and b respec-
tively ; ^shew that D, the minimum deviation of the extraordinary ray,
is given by the equation

sin 8 i)=( /W<l »-l)(/^-l).
THE END.
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LIST OF BOOKS

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MACMILLAN AND CO.
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-ffiSCHYLI Eumenides.
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