. The principles of physics. hat when it is inci-dent upon the analyzer thereis a component of the vibrationwhich is parallel to the princi-pal section, and so can be trans-mitted. As the different colorsare rotated through differentangles, the transmitted compo-nents are not mixed in thesame proportions as in the in-cident li^t, and so the field iscolored, the particular colorFig. 318. depending on the position of the analyzer. It was found that some specimens of quartz causerotation to the right ( clockwise), and so are called dextrogyrate,while others cause rotation to the left, and are
. The principles of physics. hat when it is inci-dent upon the analyzer thereis a component of the vibrationwhich is parallel to the princi-pal section, and so can be trans-mitted. As the different colorsare rotated through differentangles, the transmitted compo-nents are not mixed in thesame proportions as in the in-cident li^t, and so the field iscolored, the particular colorFig. 318. depending on the position of the analyzer. It was found that some specimens of quartz causerotation to the right ( clockwise), and so are called dextrogyrate,while others cause rotation to the left, and are called levogyrate. Many other substances, including some liquids and solutions,also possess this property, though to a much less degree. Thus,while a plate of quartz 1 mm thick rotates the plane of red lightnearly 18°, the same thickness of turpentine produces a rotation ofonly a quarter of a degree. The method of determining this angle is extremely simple. So-dium light is commonly used, and the polarizer and analyzer are. THE SACCHARIMETBR. 415 SO adjusted that the field is dark. The substance to be examinedis then inserted between them, and the analyzer is turned till thefield is again dark; the angle thus turned through is the rotationproduced by the substance. Liquids and vapors are studied byenclosing them in a tube of known length through which the polar-ized light is passed. These phenomena are explained by supposing that when a beamof plane polarized light is incident upon the quartz plate it isdoubly refracted, or divided, not into two plane-polarized beams,but into two circularly-polarized beams, the directions of motionbeing opposite. If now these traverse the crystal with slightlydifferent speeds, it is clear that when, on emerging, they are com-pounded, the resultant plane of motion and hence plane of polari-zation will not be parallel to that of the incident light. Evidentlyit will have been turned through an angle depending on the thick-ness of the crystal and
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectphysics, bookyear1895
