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8. Preliminary Note on the Connection between the Form and Optical Properties of Crystals
Published online by Cambridge University Press: 15 September 2014
Extract
1. It is the object of this note to give an account of the results of investigations, which have had for their object the discovery of the connection between the form and optical properties of crystals. It is believed that in the results here given, some of the principal difficulties of this important problem have been overcome.
2. The first step towards the solution of this problem was made by Sir David Brewster in 1818. He discovered that crystals belonging to the prismatic, oblique, and anorthic systems, are biaxal; those belonging to the pyramidal and rhombohedral systems uniaxal, while crystals of the cubic system do not possess double refraction (a fact which had been previously stated by Hauy).
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- Proceedings 1863-64
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- Copyright © Royal Society of Edinburgh 1866
References
page 247 note * Kirchhoff (Pogg. Annalen. cviii. (1859), p. 574).
page 251 note * Topaz and mica are well known examples of tins variation of the angle between the optic axes.
page 251 note † Annales de Chemie, third series, xxxiii. p. 391.
page 251 note ‡ Annales des Mines, sixth series, ii. p. 327.
page 251 note § Ibid., p. 433.
page 253 note * The measurements of Kirchhoff (Ibid.) have shown that this formula agrees closely with observation in the case of Aragonite.
Also, if a′= b′ the crystal becomes uniaxal, and the optic axes coincide with axis c′ ; hence tan 2ω ought to vanish when a′= b′.
If b′ = c′ the optic axes coincide with axis a′ ; hence tan 2ω ought to become infinite when b′= c′. Fresnel's expression fulfils these conditions.