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IX. On Circular Polarisation, as exhibited in the Optical Structure of the Amethyst, with Remarks on the Distribution of the Colouring Matter in that Mineral

Published online by Cambridge University Press:  17 January 2013

David Brewster
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Extract

In plates of Rock-Crystal cut perpendicular to the axis of the prism, an unusual kind of polarisation had been observed in the colours seen along the axis. The phenomena were subsequently analysed by M. Biot, who remarked, that in some specimens of quartz, the succession of tints appeared by turning the doubly refracting prism from right to left, while in other specimens the same succession was developed by turning the prism from left to right; and he concluded from his experiments, that the quartz impressed upon the particles of light a rotatory motion, and that this property belonged to the ultimate particles of silex, and was independent of their mode of aggregation.

The same species of colours was afterwards observed, about the same time, by MM. Biot and Seebeck, in transmitting polarised light through considerable thicknesses of some essential oils, and solutions of sugar and camphor; and this new fact seemed to confirm the supposition that the colours were not dependent upon crystallisation.

Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 9 , Issue 1 , 1823 , pp. 139 - 152
Copyright
Copyright © Royal Society of Edinburgh 1823

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References

page 141 note * After I discovered that the Agate gave a single polarised image, in consequence of the dispersion, and partial absorption, of the rays which form the other image (See Phil Trans. 1813, p. 102. and 1814, p. 189.), I employed it constantly as a part of my apparatus, as may be seen in the Phil. Trans. 1814, p. 203, 206, 208, &c. &c., and when the aid of a microscope was necessary, I cemented a thin plate, with Canada Balsam, upon the plain side of a Plano-convex Lens. By the method described in the Phil Trans. 1819, p. 146, I have extinguished one of the images of Calcareous Spar so completely, that the place where it should have been could not be distinguished, even in the strongest lights; and I have acordingly used it as an analysing prism, in preference to the agate and the tourmaline. Epidote, Mica, and other substances which absorb one of the pencils, may be employed for the same purposes.

page 141 note † See the description of the figures at the end of the paper.

page 142 note * If we consider Circular Polarisation as having its origin in a deviation from the usual laws of crystallisation, the parts of Amethyst corresponding to the black fringe may be regarded as produced under the influence of the usual laws, while, during the formation of the opposite veins, between which it is interposed, the crystallisation was subject to the unusual laws differently related to the axis, according as the polarisation is direct or retrograde.

page 143 note * See Philosophical Transactions, 1819, p. 11Google Scholar.

page 145 note * See Phil Trans. 1814, p. 192Google Scholar; and Pl V. Fig. 1, 2.

page 148 note * Plates of Rock-Crystal cut and arranged in this manner, form the best combination for exhibiting the different orders of colours.