These instruments are very sensitive, but care must be taken to avoid errors caused by changes in the relative intensities of parts of the source of light - a precaution that is sometimes overlooked in furnishing polarimeters with these analysers.
Of polarimeters for the study of rotary polarization there are three principal forms. In Wild's polaristrobometer, light from a soda flame, rendered parallel by a lens, is polarized by a Nicol's prism, and after traversing the space into which the active substance is to be inserted, falls on a Savart's plate placed in front of an astronomical telescope of low power, that contains in its eyepiece a Nicol's prism, which with the plate forms a Savart's analyser.
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