po·lar·im·e·ter 
(pō′lə-rĭmĭ-tər)
(pō′lə-rĭmĭ-tər)n.
An instrument used to measure the rotation of the plane of polarization of polarized light passing through an optical structure or sample.
po′lar·i·metric (-lər-ə-mĕtrĭk) adj.
po′lar·ime·try n.