XVIII. 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: Philosophical Transactions of the Royal Society of London
• Format: Article in Journal/Newspaper
• Language: English
• Published: The Royal Society 1815
• Subjects: Malus; Brewster; Iceland
• Online Access: http://dx.doi.org/10.1098/rstl.1815.0019; https://royalsocietypublishing.org/doi/pdf/10.1098/rstl.1815.0019

Dear Sir, The multiplication of images exhibited in some specimens of Iceland spar, appears to have been first observed by Dr. John Robison of Edinburgh, who showed the phenomenon to Mr. Benjamin Martin. Having procured several specimens that had a similar property, Mr. Martin examined them with care, and published an account of his observations in his Essay on Iceland Crystal. The experiments of Mar­tin were repeated by Mr. Brougham, who concluded that the images were produced by fractures, parallel or nearly so to the sides of the rhomboid, and Malus has more recently endeavoured to explain the phenomena, by the laws of extraordinary reflexion within doubly refracting crystals. All these philosophers agree in ascribing the multiplication of images to internal reflections, and they equally concur in regarding the colours of the images as the same with those of thin plates, and as produced by fissures, or fractures within the crystal.