PETIiOLOGICAL MICROSCOPE 



1069 



is mounted the polariser, B. capable of independent rotation like the 

 analyser, and upon the tube of the polariser is mounted a toothed 



B 



Fiu. 803. Swift's petrological microscope. 



wheel of the same size as that upon the analyser ; this wheel years 

 into a wheel carried by a tube which forms a telescopic extension of 



