A method of measuring the refractive indexes of liquids in the infrared is described. A Perkin-Elmer spectrometer is adapted for this purpose without interfering with its normal operation as a routine instrument. Although use is made of a Fabry-Perot etalon, the method is not interferometric in the accepted sense. The accuracy that has been obtained is 0.002 at a wavelength of 1μ, but in principle the possible accuracy of the method may be equal to that of the best goniometer.
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