On the multiplication of images, and the colours which accompany them in some specimens of calcareous spar. By David Brewster, LL. D. F. R. S. Lond. and Edin. In a letter addressed to the Right Hon. Sir Joseph Banks, Bart. G. C. B. P. R. S

• Published in: Abstracts of the Papers Printed in the Philosophical Transactions of the Royal Society of London
• Format: Article in Journal/Newspaper
• Language: English
• Published: The Royal Society 1833
• Subjects: Brewster; Iceland
• Online Access: http://dx.doi.org/10.1098/rspl.1815.0019; https://royalsocietypublishing.org/doi/pdf/10.1098/rspl.1815.0019

The phenomena which the author here endeavours to explain, he says, were first noticed by Prof. Robinson of Edinburgh, and pub­lished by Mr. Benjamin Martin in his Treatise on Iceland Crystal. It would not be easy to describe the appearances without reference to the figures that accompany the paper. The peculiar specimens of calcareous spar in which they occur, have been supposed to have fissures, with a disposition to split in the direction of the longer dia­gonal of the rhomboid. But the author considers it as an interrupting stratum, since it appears to him not to bear the most remote resem­blance to a fissure, but resembles a vein or film uniting the two pris­matic portions of a rhomboid. Neither are the phenomena produced, when two surfaces artificially polished in the direction of the sup­posed plane are applied to each other but they are produced when a thin film of sulphate of lime is interposed as a vein between two such portions of Iceland spar, and the surfaces are closely united by a cement of strong refractive power. The supposition of such a crystallized vein, serves also to explain the varieties observable in the characters of the phenomena in different instances, which must vary according to the thickness of the vein, and according to the position of its polarizing axis.