The diffusion coefficients D of n‐hexane and of naphthalene in a series of hydrocarbon liquids with viscosities μ from 5 · 10−4 to 5 kg m−1 sec−1 (0.5 to 5000 centipoise) have been measured at 25°C with a one Savart plate wavefront‐shearing interferometer. This apparatus allows direct determinations at effectively infinite dilution. The values obtained suggest that for a small solute diffusing in a large solvent (Formula Presented.) a result consistent with earlier studies. The exponent of 2/3 may be rationalized on the basis of the Eyring rate theory.