As a result of this work Arago constructed a polariscope, which he used for some interesting observations on the polarization of the light of the sky.
Such a section when examined in the polariscope shows an interference figure with a coloured centre, there being no black cross inside the innermost ring (this is not shown in very thin sections).
The actual details of the systems of lenses depend upon the object for which the polariscope is intended, and are given for some of the principal types of instruments in Th.
The polariscope and the spectroscope are the only instruments by the aid of which the nature of the matter can be inferred.
Superimposed sections of rightand left-handed quartz, as may sometimes be present in sections of twinned crystals, exhibit Airy's spirals in the polariscope.