( ( As ( remarked above ) ) ( , ( ( an ( optical microscope ) ) ( ( ( can only ) ( see ( something ( that ( is ( larger ( than ( ( ( about half ) ( a wavelength ) ) ( of ( visible light ) ) ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (IN As) (S (VP (VBD remarked) (ADVP (RB above))))) (, ,) (NP (DT an) (JJ optical) (NN microscope)) (VP (MD can) (ADVP (RB only)) (VP (VB see) (NP (NP (NN something)) (SBAR (WHNP (WDT that)) (S (VP (VBZ is) (ADJP (ADJP (JJR larger)) (PP (IN than) (NP (NP (QP (RB about) (PDT half)) (DT a) (NN wavelength)) (PP (IN of) (NP (JJ visible) (NN light)))))))))))) (. .)))
As remarked above, an optical microscope can only see something that is larger than about half a wavelength of visible light.
(ROOT (S (NP (PRP We)) (VP (VBP call) (NP (DT the) (JJ only) (NN light)) (SBAR (IN that) (S (NP (NNS people)) (VP (MD can) (VP (VB see) (NP (JJ visible) (NN light))))))) (. .)))