WATSON 'MICA SELENITE STAGE':

This 'Mica Selenite Stage' provides three different selenites in a slider with a rotatable mica disc above controlled by the knurled knob in center. This device reveals a wide variation in colors of polarized objects-a very entertaining accessory. The selenites have the effect of changing the coloration of objects seen under crossed polarizers. The degree of the effect varies with the type of object being studied, and different colors are imparted by different selenites; the mica allows these effects to be varied for each selenite in the slider. In use by the author, this device seems to offer slightly fewer variations than the Watson rack and pinion selenite stage which allowed the user to both rotate and combine selenites.