| http://www.w3.org/ns/prov#value | - U.S. Pat. No. 3,606,523 to G. W. Taylor entitled Fluid Variable Light Deflector, discloses apparatus for selectively changing fluids including using air under pressure to purge fluids from a liquid filled lens or prism, such fluids having differing refractive indices so as to vary a light path passing through such lens or prism.
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