polarimeter
noun
                                                                                                                            
                                                            po·lar·im·e·ter
                    
                                                                                                              
                                                                                                                                  ˌpō-lə-ˈri-mə-tər 
                                                      
                                                          
            1
                    
                                          
              
          
                                                      : an instrument for determining the amount of polarization of light or the proportion of polarized light in a partially polarized ray                                      
                
                    
2
                    
                                          
              
          
                                                      : a polariscope for measuring the amount of rotation of the plane of polarization especially by liquids                                      
                
                    
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  Merriam-Webster unabridged




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