( They ( ( are ( ( ( mirror images ) ( of ( each other ) ) ) ( that ( ( differ only ) ( in ( ( their effect ) ( on ( plane-polarized light ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP They)) (VP (VBP are) (NP (NP (NN mirror) (NNS images)) (PP (IN of) (NP (DT each) (JJ other))) (SBAR (WHNP (WDT that)) (S (VP (VBP differ) (ADVP (RB only)) (PP (IN in) (NP (NP (PRP$ their) (NN effect)) (PP (IN on) (NP (JJ plane-polarized) (NN light)))))))))) (. .)))
They are mirror images of each other that differ only in their effect on plane-polarized light.
(ROOT (S (NP (NNP Plane) (NNS mirrors)) (VP (VBP work) (SBAR (IN because) (S (NP (DT the) (JJ light) (NNS rays)) (VP (VBP create) (NP (NP (DT a) (JJ virtual) (NN image)) (PP (IN behind) (NP (DT the) (NN mirror)))))))) (. .)))