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XIX. On certain new Phenomena of Colour in Labrador Felspar, with Observations on the nature and cause of its Changeable Tints

Published online by Cambridge University Press:  17 January 2013

David Brewster
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Extract

Sir Isaac Newton's theory of the colours of natural bodies, is perhaps the most ingenious and lofty of all his speculations. It was devised, however, at a time when the doctrine of light had made comparatively but little progress, and before the discovery of various principles on which the colours of bodies must depend, or by which, at least, they must be extensively modified. The different dispersive powers of transparent substances;—the irrationality of the spectrum;—the action of striated surfaces;—the decomposition of polarised light;—the reflection of coloured light at the confines of equally refracting media;—and the absorption of common and of polarised rays,—are principles which embrace within their individual range a great variety of facts to which the Newtonian theory of colours bears no relation.

Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 11 , Issue 2 , 1831 , pp. 322 - 331
Copyright
Copyright © Royal Society of Edinburgh 1831

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References

page 324 note * Oil of Cassia would have been preferable in other cases, but as it has a colour of its own, and disperses light so powerfully, it was unsuitable where delicate tints were to be observed.

page 325 note * It is from this cause that the splendid colours arise which accompany the dendritic crystallizations of titanium in mica, which I have examined with much attention.

page 328 note * Elles proviennent, comme dans l'opal, des legeres fissures qui interrompent le tissue de la pierre; mais l'opale etant fendillée dans toutes sortes des directions, presente des reflets qui se succedent, à mesure qu'on la fait mouvoir, au lieu que dans le feldspath, dont les fissures coincident sur un seul plan; en sorte qu'ils se montrent tout entiers, lorsque la lumière est reflechie par ce plan, sous l'angle favorable pour la renvoyer à l'oeil, et disparoissent, des qu'on donne à la pierre un inclination differente. J'ai reconnu en observant un morceau de feldspath opalin de Norwege, qui m'a été envoyé par M. Esmark, que les plans d'ou partoient les reflets dont je viens de parler, etoient dans le sens des faces T qui sont les plus etendues.—Traité de Mineralogie, tom. ii. p. 613.

page 329 note * The demonstration of this is very simple. Through C and B draw Bn, and FCQ perpendicular to DC, and through A draw AF perpendicular to DQ, and meeting Bn in n. Then x = CDA = AFQ = AnB, and BAF = ABn + A n B = B + x. But FAC = ACQ — AFC; consequently, since FAC = BAF, and ACQ = A, we have

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page 330 note * Traité, tom. ii. p. 606.