A treatise on optics / by David Brewster.

  • Brewster, David, 1781-1868
Date:
1831 [i.e. 1840?]
Catalogue details

Licence: Public Domain Mark

Credit: A treatise on optics / by David Brewster. Source: Wellcome Collection.

    233/400 (page 221)
    that it is not possessed by opal, tabasheer, and other sili- ceous hodies_, and that it disappears in melted quartz. Mr. Herschel also found that it does not exist in a solu- tion of silex in potash. Hitherto no connection could be traced between the Fig. 112. right and left-handed structure in quartz^ and the crystalline form of the specimens which possessed these properties. Mr. Herschel_, however_, discovered that the plagiedral quartz which contains unsymmetrical faces^ oo sc cc, fig. 112.;, turns the planes of polarisation in the same direction in which these faces lean round the summits A a; sc, a sc sc. — /^yli Circular Polarisation in Fluids. (128.) The remarkable property of polarising light circularly occurs in a feeble degree in certain fluids_, in which it was discovered by M. Biot and Dr. Seebeck. Mr. Herschel has found it in camphor in a solid state^ and I have discovered it in certain specimens of unannealed glass. If we take a tube six or seven inches long, and fill it with oil of turpentine, and place it in the appa- ratus, fig. 94., so that polarised light transmitted through the oil may be refiected to the eye from the plate C, we shall observe the complementary colours and a distinct ro- tation of the plane of polarisation from righttolefit. Other fluids have the property of turning the planes of polar- isation from lefit to right, as shown in the following table, which contains the results of M. Biot’s experiments. Crystals which turn the Planes from Eight to Lefit. Arc of Rotation for every 25th of an inch in Thickness. Relative Thick- nesses that pro- duce the same Effect. Rock crystal . . . - jOil of turpentine - - - - Solution of 1753 parts of artificial cam. | phor in 17.359 of alcohol - - j Essential oil of laurel. 180-414 0-270 0-018 1 68|