No CrossRef data available.
We use cookies to distinguish you from other users and to provide you with a better experience on our websites. Close this message to accept cookies or find out how to manage your cookie settings.
We use cookies to distinguish you from other users and to provide you with a better experience on our websites. Close this message to accept cookies or find out how to manage your cookie settings.
Published online by Cambridge University Press: 14 March 2018
Certain optical properties of crystals, and more particularly the refractive index, may be determined either in the directions-image, often referred to as the 'image in convergent light', or in the ordinary object-image in which the object itself is seen. In the former case, in which the index of refraction is 'usually determined by means of the critical angle of total-reflection, every point in the image corresponds to a single direction of propagation of the wave-front through the crystal-structure and to the two corresponding directions of vibration. One of these can, however, be eliminated by the insertion of a nicol in an approximate position, and thus all ambiguity in the determination of the refractive index is removed.
page 131 note 1 Evans, J. W., 'The isolation of the directions-image of small objects', Mineralogical Magazine, 1916, this vol., p. 45 CrossRefGoogle Scholar.
page 132 note 1 Sorby, H. C., Mineralogical Magazine, 1877, vol. i, p. 97 ; 1909, vol. xv, p. 189Google Scholar.