On the oblique refraction of Iceland crystal

• 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 1832
• Subjects: Wollaston; Iceland
• Online Access: http://dx.doi.org/10.1098/rspl.1800.0056; https://royalsocietypublishing.org/doi/pdf/10.1098/rspl.1800.0056

In the preceding communication Dr. Wollaston inserted two dif­ferent measures of refractive powers distinctly observable in the Ice­land crystal, as well as an estimate of its dispersive power; but he has reserved for this treatise some remarks, which the same mode of investigation has enabled him to make on its oblique refraction. To this he was led by the consideration that the law to which Huygens had reduced this refraction, however founded in truth, could not be easily verified by any of the former methods of measurement. According to the Huygenian hypothesis, light proceeding from any luminous centre is propagated by vibrations of a medium highly elastic, that pervades all space. In ordinary cases the incipient un­dulations are of a spherical form; but in the Iceland crystal they appeared to him to be portions of an oblate spheroid, of which the axis is parallel to the short diagonal of an equilateral piece of crystal, and its centre the point of incidence of the ray. Hence he deduced a ratio between the sine of incidence, and the sine of refraction (that is, the ordinate of the spheroidical undulation) in any section of the spheroid.