The real and imaginary parts of the complex index of refraction in theR‐line region of ruby have been measured near liquid‐nitrogen temperature with sufficient resolution that theR‐line doublet structure was well resolved. A modification of the usual Babinet compensator technique was used for the refractive‐index measurements, which were found to correlate with the absorption measurements as predicted by the Kramers‐Kronig relations. An attempt at direct quantitative verification of the dispersion relations for an optically pumped sample is also described.